Re: [Tsv-art] [nvo3] Tsvart last call review of draft-ietf-nvo3-vmm-04

Bob Briscoe <ietf@bobbriscoe.net> Fri, 27 March 2020 15:23 UTC

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To: Linda Dunbar <linda.dunbar@futurewei.com>, "Black, David" <David.Black@dell.com>, "Bocci, Matthew (Nokia - GB)" <matthew.bocci@nokia.com>, "sarikaya@ieee.org" <sarikaya@ieee.org>
Cc: "tsv-art@ietf.org" <tsv-art@ietf.org>, NVO3 <nvo3@ietf.org>, "draft-ietf-nvo3-vmm.all@ietf.org" <draft-ietf-nvo3-vmm.all@ietf.org>
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From: Bob Briscoe <ietf@bobbriscoe.net>
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Subject: Re: [Tsv-art] [nvo3] Tsvart last call review of draft-ietf-nvo3-vmm-04
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Linda, inline...

On 26/03/2020 23:28, Linda Dunbar wrote:
>
> David,
>
> Thank you for reviewing the revised version and providing more comments.
>
> Resolution to your comments are inserted below marked with [Linda]  :
>
> Thank you. Linda
>
> *From:*Black, David <David.Black@dell.com>
> *Sent:* Wednesday, March 25, 2020 8:13 PM
> *To:* Linda Dunbar <linda.dunbar@futurewei.com>om>; Bob Briscoe 
> <ietf@bobbriscoe.net>et>; Bocci, Matthew (Nokia - GB) 
> <matthew.bocci@nokia.com>om>; sarikaya@ieee.org
> *Cc:* tsv-art@ietf.org; NVO3 <nvo3@ietf.org>rg>; 
> draft-ietf-nvo3-vmm.all@ietf.org; Black, David <David.Black@dell.com>
> *Subject:* RE: [Tsv-art] [nvo3] Tsvart last call review of 
> draft-ietf-nvo3-vmm-04
>
> Quick responses based on the recently posted -08 version and the 
> discussion below.
>
> [A] & [B] – Informational as intended RFC status is ok.
>
> The RFC 2119/RFC 8014 keyword boilerplate needs to be removed from 
> Section 2, as none of those keywords are now used.
>
> [Linda] Okay removed, though I did see other Informational drafts have 
> this statement.
>
> [C] Hot and cold standby are still problem areas:
>
> [Linda] This document only covers the case of VM moves being Planned.
>
> ...
>
> [Linda] “Standby modes of VM movement” is out of the scope of this 
> document as indicated in the newly inserted statement in the 
> Introduction.
>
> Section 8 on the Hot Standby mechanism needs to be removed from the 
> draft, as the Hot Standby mechanism is a fault tolerance mechanism 
> that is primarily intended for Unplanned moves, e.g., as the draft 
> states: If the VM in the primary NVE fails, there is no need to 
> actively move the VM to the secondary NVE because the VM in the 
> secondary NVE already contain identical information.
>
> [Linda]  Section 8 is on “Other Options”. Hot Redundancy is one option 
> that doesn’t require moving VM in case anything happens. Removed the 
> word “VM Mobility” from the title. Since this is an informational 
> draft, the “Other Option” is to give a perspective of other ways to 
> achieve reliability.
>

[BB] Is any of section 8 relevant to the scope of the draft now?

I thought achieving reliability would be out of scope, now you've said 
(a couple of paras earlier): "This document only covers the case of VM 
moves being Planned" and "“Standby modes of VM movement” is out of the 
scope of this document". Surely, no-one can improve reliability with 
only planned moves. Reliability is all about unplanned moves.


> In addition, the “cold standby entity” in Section 7 should be renamed 
> to something more meaningful.
>
> [Linda] How about changing the text to the following?
>
> The Cold VM mobility can be facilitated by VM management system to 
> exchange the needed states between the Old NVE and the New NVE. The 
> cold mobility option can be used for non-critical applications and 
> services that can tolerate interrupted TCP connections.
>

[BB] It's not just S.8. In S.7 (of draft-09), there's still the 
following text (which was what I was originally talking about when I 
raised this concern):

      The Warm VM mobility refers the backup entities receive backup
      information at more frequent intervals.  The duration of the
      interval determines the warmth of the option.  The larger the
      duration, the less warm (and hence cold) the Warm VM mobility
      option becomes.


As far as I understand it, text that talks about backup entities 
receiving backup info at frequent intervals is describing standby for 
failover, not mobility. Even tho the text gives it the name "Warm VM 
Mobility", the meaning of all the words is surely about standby and 
failover.

> [D] The suggested NVO3 gateway text is incorrect because it includes 
> this statement:
>
> > RFC 8014 (Section 5.3) has the discussion whether a VM move may result in or 
> cannot result in a change to the network node providing the NV03 
> Gateway functionality
>
> Section 5.3 of RFC 8014 does not contain that discussion; please do go 
> read RFC 8014.  That discussion (which is specific to VM mobility) 
> needs to be written and added to this draft.
>
> [Linda] sorry, I literally took your wording. Change the text to the 
> following to amend what is missing from RFC8014.
>
> Inter VNs (Virtual Networks) communication refers to communication 
> among tenants (or hosts) belonging to different VNs. Those tenants can 
> be attached to the NVEs co-located in the same Data Center or in 
> different Data centers. This document assumes that the inter-VNs 
> communication is via the NVO3 Gateway as described in RFC8014 (NVO3 
> Architecture). RFC 8014 (Section 5.3) describes the NVO3 Gateway 
> function which is to relay traffic onto and off of a virtual network, 
> i.e. among different VNs.
>
> After a VM is moved to a new NVE, the VM’s corresponding Gateway may 
> need to change as well. If such a change is not possible, then the 
> path to the external entity need to be hair-pinned to the NVO3 Gateway 
> used prior to the VM move.
>

[BB] Works for me.

Nonetheless, surely this doesn't just apply to inter-VN communication. 
Inter-communication through an NVO3 Gateway equally applies to 
communication with any external entity, whether in another VN or just in 
another N (without the V, I mean just any other network, whether virtual 
or not).

> [E] Two parts
>
> E-a) Section 4.2.1 is now Section 4.3 and the new text is an 
> improvement, but it would be even clearer to remove the term “Task” 
> entirely from this draft, as the scope (stated in the Introduction and 
> Abstract) is VM mobility. Discussion about application of the 
> techniques described in this draft to entities other than VMs should 
> be placed in a separate new section near the end of the draft to avoid 
> confusing readers.  This would also address a significant portion of 
> Bob’s “new problem” below.
>
> [Linda] Okay, removed.
>
> E-b) Discussion of ICMP effects has not been added.   If that 
> discussion is not going to be added, then the text on use of ICMP 
> needs to be removed.
>
> [Linda] Okay, removed.
>

[BB] Can you explain (at least in this email) what you think is meant by 
the following sentence:

      impact is relatively small when TCP
      connections are automatically closed in the network stack during a
      migration event.


I think this is saying that network elements close TCP connections. 
Normally only a host participating in a connection can close it. The 
only way a network element would be able to close a TCP connection would 
be to spoof RST or FIN packets (if the TCP connection is not 
authenticated or encrypted). Is this what is meant?

On the other hand, if it means the network discards all packets, that 
will probably eventually cause something on one of the end-hosts to time 
out and close the connection, but it will be a long and painful way to 
close a connection, lasting perhaps tens of minutes or longer.

Similarly, it's not clear what the subject of this sentence is, i.e. 
what is doing the pausing:

     More involved approach to connection migration entails pausing the
      connection, packaging connection state and sending to target,
      instantiating connection state in the peer stack,


As above, normally only a host can pause one of its TCP connections. But 
everything else in the draft is talking about actions taken by network 
elements. So if this does mean the host is in control of pausing, it 
needs to make that clear, and describe how the network communicates the 
need to pause to each application.


> [F] Security Considerations are still a problem – the added security 
> text is not specific to VM mobility.
>
> [Linda] How about changing to the following:
>
> Security threats for the data and control plane for overlay networks 
> are discussed in [RFC8014].  ARP (IPv40 and ND (IPv6) are not secure, 
> especially if we accept gratuitous versions in multi-tenant environment.
>
> In Layer-3 based overlay data center networks, the problem of address 
> spoofing may arise.  An NVE may have untrusted VMs attached. This 
> usually happens in cases like the VMs running third party 
> applications.  Those untrusted VMs can send falsified ARP (IPv4) and 
> ND (IPv6) messages, causing NVE, NVO3 Gateway, and NVA to be 
> overwhelmed and not able to perform legitimate functions. The attacker 
> can intercept, modify, or even stop data in-transit ARP/ND messages 
> intended for other VNs and initiate DDOS attacks to other VMs attached 
> to the same NVE.
>
> This requires VM management system to apply stronger security 
> mechanisms when add a VM to an NVE. VM Management system is out of 
> scope of this document.
>

[BB] With the L3 VM mobility cases that are still included in scope, a 
new secure binding needs to be instantiated between the unchanged 
identifier and the new locator. This is unlikely to be something that a 
'VM management system' will be in a position to do, because it involves 
e2e checks that a message from one IP address to another and the 
response back to the first address, actually get routed back to the 
originator.

The locator-identifier mechanism given as an example (ILA) doesn't 
include secure binding, AFAICT. BTW, the cited ILA draft is the old one 
(draft-herbert-nvo3-ila), which has now moved to 
draft-herbert-intarea-ila. And even that expired 18 months ago. Its 
doesn't discuss how to securely bind the new locator to the identifier. 
There are just some fairly high level comments in the security 
considerations section about using IPSec or GUESEC, both of which have 
nothing to do with securing the binding between locators and identifiers 
nor protecting against IP address spoofing (they protect the 
/information/ in the connection, not the integrity of the address 
bindings). Similarly, draft-herbert-ila-mobile has some discussion of 
security, but not of the binding between locator and identifier (again 
AFAICT).

So, if it's still appropriate to use ILA as an example, I think this 
security gap needs to be highlighted in the Security Considerations 
section of nvo3-vmm. Alternatively you might want to refer to another 
example mechanism, such as HIP, which was designed for IP address 
mobility using a secure binding between the identifier and each locator. 
However, I have no idea whether other aspects of HIP would make it 
inapplicable for VM Mobility.


> -------
>
> For completeness, here are the remaining 3 structure and 
> comprehensibility problems that Bob noted:
>
>  2. [NOT ADDRESSED] Signposting of where sub-cases start and end in S.4.1
>
> [Linda] changed.
>

[BB] 4.2 (which was 4.1) still reads as one long block of prose with no 
clear indication of where the different cases stop. The main problem is 
the case where the client requests the same MAC address. This para seems 
to have been inserted into the IPv4 case, half-way through, and it's not 
clear that it ends and goes back to other matters to do with the IPv4 
case. It's also not clear why a client requesting the same MAC address 
isn't addressed under the IPv6 case. Here (again) are the 4 different 
parts of this subsection that I could identify:

* IPv4
* end-user client
* 2 paras starting "Other NVEs communicating with this virtual 
machine..." [Not clear that the end-user case has ended and we have 
returned to the general IPv4 case?]
* IPv6 [Strictly, it still hasn't said whether the end-user client case 
has ended.] [Also, it doesn't explain why there is no need for an 
end-user client case under IPv6?]

>  3. [NOT ADDRESSED] Indecision over whether packets are silently
>     dropped, dropped with an ICMP message, forwarded or tunnelled.
>
> [Linda] removed the ICMP discussion.
>

[BB] The ICMP text was a different problem, not this one. This one is 
about how there's no clear structure to say which solution is used in 
which circumstances. Tunnelling comes up in the L2 section, packet drop 
comes up here and there, but it says it can also forward packets, 
without saying why it would drop packets if it could forward them. You 
can close TCP connections. You can pause them. It's written like 
"Whatever; You can do this, or that or the other. Do what you want. 
Whatever. Am I bovvered? Look at my face. Is my face bovvered? Whatever."


>  4. [NOT ADDRESSED] The order in which the various stages of mobility
>     occur was jumbled. Some stages have been ruled out of scope, but
>     they are still mentioned in jumbled order.
>
> [Linda] add the reference to RFC7666 that describe the states and MIBs 
> of VMs managed by Hypervisor.
>

[BB] The order of text in this draft will not be solved by referring to 
another draft that gives things in the right order.

> Thanks, --David
>

[BB] Thanks to David for helping me out here. And thanks to Linda for 
starting to get to grips with this draft. I hope you can see now that it 
was not in good shape.

I'm still wanting to know why the IETF needs to publish this draft (and 
therefore why we're all having to sink our time into getting it into 
shape). As more and more of it is being removed as out of scope, I'm 
even less certain who is going to ever read this draft, or why they 
would need to.



Bob



> *From:*Linda Dunbar <linda.dunbar@futurewei.com 
> <mailto:linda.dunbar@futurewei.com>>
> *Sent:* Wednesday, March 25, 2020 1:47 PM
> *To:* Black, David; Bob Briscoe; Bocci, Matthew (Nokia - GB); 
> sarikaya@ieee.org <mailto:sarikaya@ieee.org>
> *Cc:* tsv-art@ietf.org <mailto:tsv-art@ietf.org>; NVO3; 
> draft-ietf-nvo3-vmm.all@ietf.org <mailto:draft-ietf-nvo3-vmm.all@ietf.org>
> *Subject:* RE: [Tsv-art] [nvo3] Tsvart last call review of 
> draft-ietf-nvo3-vmm-04
>
> [EXTERNAL EMAIL]
>
> David and Bob,
>
> Thank you very much for the prompt replies and comments.
>
> Inserted below are the proposed resolutions to your comments and 
> suggestions.
>
> Linda
>
> *From:*Black, David <David.Black@dell.com <mailto:David.Black@dell.com>>
> *Sent:* Tuesday, March 24, 2020 10:05 PM
> *To:* Bob Briscoe <ietf@bobbriscoe.net <mailto:ietf@bobbriscoe.net>>; 
> Linda Dunbar <linda.dunbar@futurewei.com 
> <mailto:linda.dunbar@futurewei.com>>; Bocci, Matthew (Nokia - GB) 
> <matthew.bocci@nokia.com <mailto:matthew.bocci@nokia.com>>; 
> sarikaya@ieee.org <mailto:sarikaya@ieee.org>
> *Cc:* tsv-art@ietf.org <mailto:tsv-art@ietf.org>; NVO3 <nvo3@ietf.org 
> <mailto:nvo3@ietf.org>>; draft-ietf-nvo3-vmm.all@ietf.org 
> <mailto:draft-ietf-nvo3-vmm.all@ietf.org>; Black, David 
> <David.Black@dell.com <mailto:David.Black@dell.com>>
> *Subject:* RE: [Tsv-art] [nvo3] Tsvart last call review of 
> draft-ietf-nvo3-vmm-04
>
> Trying to help out – here are some summarized comments on the first 
> six issues that Bob listed as not addressed – this summary does not 
> include the requests for a serious editorial pass and draft 
> restructuring for clarity.
>
> -- [A] Purpose of draft &
>
> -- [B] Normative text
>
> The draft header indicates that its intended status is Informational, 
> but the datatracker indicates Best Current Practice (BCP).   Which one 
> is correct?
>
> The answer to that question affects what to do about the two instances 
> of “MUST”.   Based on what I see in this draft, Informational seems 
> more appropriate than BCP.
>
> [Linda] agree with you. Will ask the NV03 Chair to change the status 
> to “Informational” to be consistent with the status stated in the 
> draft. The two instances of “MUST” has been removed in 08 version.
>
> -- [C] VM mobility vs. VM redundancy
>
> Bob> #. The draft silently slips back and forth between VM mobility 
> and VM redundancy,
>
> It does indeed, almost exactly as Bob describes:
>
> [BB] In -07 warm standby is still described as it was in -04: state 
> update messages at regular intervals. That is redundancy, not mobility.**
>
> With one exception - the draft discusses hot and cold standby, but not 
> warm standby – I think Bob meant to refer to cold standby.  That said ...
>
> The crucial distinction that the draft needs to make clear is between 
> planned moves, i.e., mobility, and unplanned moves, i.e., 
> standby-based failover (in this context, “failover” is a better word 
> than “redundancy”).  In both cases, network connections have to be 
> moved and/or re-established, and the mechanisms to do so are related 
> which is why it makes sense for the draft to cover both classes of 
> mechanisms.
>
> [Linda] This document only covers the case of VM moves being Planned. 
> Even with Cold Migration, it is referring to VM Management System 
>  informs the VM in the Location (NVE) to be launched. I can add the 
> following statement in the introduction in 08 version to make it clear:
>
> This document is strictly within the DCVPN, as defined by the NVO3 
> Framework [RFC 7365]. The intent is to describe Layer 2 and Layer 3 
> Network behavior when VMs are moved from one NVE to another. This 
> document assumes that the VMs move is initiated by VM management 
> system, i.e. planed move. How and when to move VM are out of the scope 
> of this document. RFC7666 already has the description of the MIB for 
> VMs controlled by Hypervisor. The impact of VM mobility on higher 
> layer protocols and applications is outside its scope.
>
> The Standby modes of VM movement are missing from the conventions in 
> Section 2, and the distinction between planned and unplanned moves 
> should be made clear there or in Section 3 before getting into the 
> details of the specific modes. I’ll also observe that Section 8 leaves 
> out a lot of the details that are required to make Hot Standby work, 
> and in particular, “provide services simultaneously as in load-share 
> mode of operation” is not possible in all situations – if the VM has 
> significant internal state then load balancing among the two VMs may 
> cause failover to behave incorrectly because the VM that is failed 
> over to will have different internal state from the failed VM.
>
> [Linda] “Standby modes of VM movement” is out of the scope of this 
> document as indicated in the newly inserted statement in the 
> Introduction.
>
> I also suggest that the authors look at RFC 7666 which contains a 
> state machine for VM states – use of that state machine and the states 
> that it contains may help improve the explanation of the various VM 
> movement mechanisms in this draft.
>
> [Linda] the reference to RFC7666 including the state machine is added 
> to the introduction and to Section 4.2. The state machine of VMs is 
> referenced in Section 4.2.
>
> RFC7666 has the more detailed description of the State Machine of VMs 
> controlled by Hypervisor.
>
> -- [D] External entities.
>
> Bob> #. Applicability is fairly clearly outlined, but it is not clear 
> whether hosts corresponding with the mobile VMs are part of the same 
> controlled environment or on the uncontrolled public Internet.
>
> I see ... Bob’s comment needs to be translated into NVO3 terminology 
> ... just a minute, bear with me ...
>
> What Bob is asking for is a discussion of how things work when an NVO3 
> Gateway provides connectivity between the VM and an external entity 
> outside the NV Domain.  The authors should refer to Section 5.3 of RFC 
> 8014 (NV03 Architecture), and discuss the resulting implications, 
> including whether a VM move may result in or cannot result in a change 
> to the network node providing the NV03 Gateway functionality – if such 
> a change is not possible, then the path to the external entity may be 
> hair-pinned to the NVO3 Gateway used prior to the VM move.
>
> [Linda] The current Introduction already stated that the 
> communications are among VMs within the DC and with External entities.
>
> There are communications among tasks belonging to one tenant and 
> communications among tasks belonging to different tenants or with 
> external entities.
>
> I can add your suggested wording to the Section 4:
>
> This document assumes that the communication with external entities 
> are via the NVO3 Gateway as described in RFC8014 (NVO3 Architecture). 
> RFC 8014 (Section 5.3) has the discussion whether a VM move may result 
> in or cannot result in a change to the network node providing the NV03 
> Gateway functionality – if such a change is not possible, then the 
> path to the external entity may be hair-pinned to the NVO3 Gateway 
> used prior to the VM move.
>
> [E]  Section 4.2.1 is problematic.
>
> E-a) Bob and the authors appear to be talking past each other, as the 
> VM’s IP addresses do not change as a consequence of what Section 4.2.1 
> describes.   However, Section 4.2.1 is sufficiently poorly written 
> that it lead Bob to the conclusion that the VM’s IP addresses do 
> change ... and looking at  that text now as if I knew nothing about VM 
> mobility, I can see how that text could lead a non-expert reader to 
> that incorrect conclusion.  In particular, identifier/locator 
> separation is not necessary for what’s going on in Section 4.2.1.
>
> [Linda] Revise the 4.2.1  description to the following:
>
> The term “Task” is referring to an entity (Task) that is instantiated 
> on a VM or a container, in another word, a Task can be an 
> “Application” or a “workload” running on a VM or a Container.
>
> Moving a Task running on a VM attached to one NVE to another VM 
> attached to a New NVE is same as moving the VM from one NVE to the New 
> NVE. The VM attached to the New NVE needs to be assigned with the same 
> address as VM attached to the Old NVE, which is called Address 
> Migration in this document. Here is an example of the steps involved 
> in Address Migration:
>
>   * Configure IPv4/v6 address on the target VM/NVE.
>   * Suspend use of the address on the old NVE.  This includes handling
>     established connections.  A state may be established to drop
>     packets or send ICMPv4 or ICMPv6 destination unreachable message
>     when packets to the migrated address are received. Referring to
>     the VM State Machine described in RFC7666.
>   * Push the new NVE-VM mapping to other NVEs which have the attached
>     VMs communicating with the VM being moved.  All relevant NVEs will
>     learn the new mapping via their corresponding NVA.
>
> E-b) Also ...
>
> Bob> For useful tutorial on how TCP responds to ICMP destination 
> unreachable messages
>
> ...
>
> [Linda] Layer 4 connection state handling is out of the scope of NVo3.
>
> It appears that “Layer 4 connection state handling” includes the 
> effects of ICMP messages on connections.  That may be outside the 
> scope of NVO3, but it is within the scope of this draft because the 
> draft discusses sending “ICMPv4 or ICMPv6 destination unreachable 
> message when packets to the migrated address are received.”   Having 
> brought up that concept, the draft is responsible for discussing the 
> effects and consequences of sending such messages.  If the authors do 
> not intend to discuss that topic, then Section 4.2.1 ought to be removed.
>
> [F] Security considerations
>
> Bob> #. Security Considerations: repeats issues in other drafts that 
> are not specific to mobility, but it does not mention any security 
> issues specifically due to VM mobility.
>
>
> That looks like a problem, if for no other reason than a SECDIR review 
> of the DetNet MPLS data plane draft has raised the analogous issue 
> with that draft.  I don’t see a SECDIR review for this draft in the 
> data tracker – I suggest that the draft shepherd ask for a SECDIR 
> review and ensure that this concern is brought to the attention of the 
> SECDIR reviewer.
>
> [Linda] Security specific to VM Mobility has the following:
>
> There are several issues in a multi-tenant environment that create 
> problems.  In Layer-2 based overlay data center networks, lack of 
> security in VXLAN, corruption of VNI can lead to delivery to wrong 
> tenant.  Also, ARP in IPv4 and ND in IPv6 are not secure, especially 
> if we accept gratuitous versions.  When these are done over a UDP   
> encapsulation, like VXLAN, the problem is worse since it is trivial 
> for a non-trusted entity to spoof UDP packets.
>
> Thanks, --David
>
> *From:*Tsv-art <tsv-art-bounces@ietf.org 
> <mailto:tsv-art-bounces@ietf.org>> *On Behalf Of *Bob Briscoe
> *Sent:* Tuesday, March 24, 2020 7:34 PM
> *To:* Linda Dunbar; Bocci, Matthew (Nokia - GB); sarikaya@ieee.org 
> <mailto:sarikaya@ieee.org>
> *Cc:* tsv-art@ietf.org <mailto:tsv-art@ietf.org>; NVO3; 
> draft-ietf-nvo3-vmm.all@ietf.org <mailto:draft-ietf-nvo3-vmm.all@ietf.org>
> *Subject:* Re: [Tsv-art] [nvo3] Tsvart last call review of 
> draft-ietf-nvo3-vmm-04
>
> [EXTERNAL EMAIL]
>
> Linda,
>
> On 24/03/2020 20:10, Linda Dunbar wrote:
>
>     Bob,
>
>     With regard to the purpose of the document, the Abstract stated
>     very clearly:
>
>     This document describes virtual machine mobility solutions
>     commonly used in data centers built with overlay-based network.
>     This document is intended for describing the solutions and the
>     impact of moving VMs (or applications) from one Rack to another
>     connected by the Overlay networks.
>
>     The Purpose is “for describing the solutions and the impact of
>     moving VMs (or applications) from one Rack to another connected by
>     the Overlay networks.”
>
>
> [BB2] I quoted those sentences to you myself. I explained that they 
> are what the document is about. But they are not a reason for why the 
> IETF is publishing it.
>
>     Other changes and reply to  your comments are inserted below.
>     Please let us know as soon as possible (hopefully not another 3
>     months) if they are acceptable?
>
>
> [BB2] I felt guilty about not having noticed the emails about this. 
> Until I read it. Then I thought about the few days work I had put into 
> that review (I am not employed by anyone - I do this on my own time). 
> And of the 14 main points I made, only the 5 easy ones had been 
> addressed and the 9 main ones had been completely ignored.
>
> Anyway, my email was to Matthew as document shepherd. As I said below, 
> I believe my role as a reviewer is not to decide whether this document 
> is acceptable. It is to state which of my review comments have not 
> been addressed, say how important I think each is, and clarify to 
> remove any misunderstanding. Then it is up to Matthew to decide what 
> you need to do (or not).
>
> Nonetheless, I am particularly concerned about the descriptions of 
> connections being paused or stopped, which are so far from how TCP/IP 
> works, that it makes me certain that this document is a fantasy - it 
> can never have been implemented. Or if it has been, there must be some 
> major assumptions about the applications in this multi-tenant DC that 
> are not being stated.
>
> more...
>
>     Linda Dunbar
>
>     *From:*Bob Briscoe <ietf@bobbriscoe.net> <mailto:ietf@bobbriscoe.net>
>     *Sent:* Monday, March 23, 2020 6:59 AM
>     *To:* Bocci, Matthew (Nokia - GB) <matthew.bocci@nokia.com>
>     <mailto:matthew.bocci@nokia.com>; sarikaya@ieee.org
>     <mailto:sarikaya@ieee.org>
>     *Cc:* tsv-art@ietf.org <mailto:tsv-art@ietf.org>; NVO3
>     <nvo3@ietf.org> <mailto:nvo3@ietf.org>;
>     draft-ietf-nvo3-vmm.all@ietf.org
>     <mailto:draft-ietf-nvo3-vmm.all@ietf.org>
>     *Subject:* Re: [nvo3] [Tsv-art] Tsvart last call review of
>     draft-ietf-nvo3-vmm-04
>
>     Matthew,
>
>     It is a long time since I reviewed this (Sep 2018), and I'm sorry
>     for being unresponsive back in Aug 2019 when the -05 revision that
>     aimed to address my -04 review comments was released.
>
>     I have to say, IMO this document is still far from suitable for
>     publication as an RFC. The IETF surely cannot publish material
>     that demonstrates such a loose grasp of the subject area,
>     particularly the impact of mobility on layer 4 and above. However,
>     that is not my call. All I can do as a reviewer is identify those
>     of my comments that have not been addressed, and why it is
>     important to address them. Then you, as document shepherd, can
>     decide whether the IESG will need these issues to be addressed.
>
>     So, below, I work through my previous top level comments,
>     identifying whether they have been addressed or not. I assume the
>     editorial nits that I identified have been addressed (I haven't
>     checked).
>
>     I also have to say that, as a general rule, the only ones of my
>     review comments that have been addressed are the 'easy' ones that
>     could be dealt with using something like find-and-replace
>     techniques. Those that question the subject matter itself, have
>     usually not been addressed at all.
>
>     =================================
>
>         #. The introduction does not say what the purpose of
>         publishing this draft is.
>
>
>     *[NOT ADDRESSED]*
>
>     [BB] Changing the intended status to Informational has helped to
>     address some of my concerns. However, an informational document
>     still has to have a target readership and a purpose. This vmm
>     document still doesn't seem to have a purpose, or if it does, it
>     doesn't say what's its purpose is.
>
>     When it says it...
>      ...describes solutions that support VM mobility,
>
>     or that:
>      ...there is a desire to document comprehensive VM mobility
>     solutions that cover
>          both IPv4 and IPv6.
>
>     ...they are not reasons for the IETF to publish an informational
>     RFC. They are circular reasons - they just say, "we are writing
>     this because it describes something". They do not say why it is
>     relevant for the IETF to publish this description. Is it something
>     that the IETF needs to understand before it moves in to
>     standardize aspects of VM mobility? Does this document provide new
>     insights that have not been understood before? Do multiple VM
>     mobility solutions already exist, but a standard is needed,
>     because they don't interoperate?
>
>         #. It does not seem as if the NVO WG has discussed the purpose
>         of using normative text in this draft. See detailed comments.
>
>
>     *[NOT ADDRESSED]*
>
>     [BB] In -07 there are still the same two "MUSTs" as in -04. This
>     is intended to be an informational RFC, so no-one will be required
>     to comply with it. Admittedly, informational RFCs can contain
>     normative keywords in certain special cases (e.g. an informative
>     copy of a specification of a protocol that is outside the IETF's
>     change control). But this draft is not one of those special cases.
>
>     By my understanding of what normative keywords are for, these
>     "MUSTs" ought to be replaced with "has to" or "needs to".
>
>     [Linda] How about changing to the following?
>
>     The Old NVE needs totunnel these in-flight packets to the New NVE
>     to avoid packets loss.
>
>
> [BB2] Yup. But before you start making minor tweaks, let's jump to the 
> point about stopping and pausing connections, which I think throws the 
> whole document into doubt...
>
>         #. The draft silently slips back and forth between VM mobility
>         and VM redundancy, without recognizing the differences. See
>         detailed comments.
>
>     [Linda] There is no single mention of VM Redundancy in the 07
>     version. What do you mean?  “Warm Mobility” depends on having
>     relevant information (or status) about the VM at the target
>     location.  That is different from running redundant instance at
>     the target location.
>
>     *[NOT ADDRESSED]*
>
>     [BB] In -07 warm standby is still described as it was in -04:
>     state update messages at regular intervals. That is redundancy,
>     not mobility. In particular, Section 7 has VM Mobility in the
>     title, but starts slipping into talking about standby after the
>     second para.
>
>     [Linda] In this document, the definition of “WARM Mobility” is
>     referring to having the VM’s relevant information on the target
>     location.
>
>
>     Warm standby is useful for resilience against failures, but it is
>     not mobility. In standby, processing does not /move/, which is
>     what /mobility/ means. Standby never releases the 'Old' address
>     and, because there is no first move there is never a second or
>     subsequent move. So routing and addressing does not become
>     increasingly fragmented.
>
>     [Linda] this document doesn’t address the concept of “Warm Standby”.
>
>
>     As the Intro says, the purpose of VM mobility is...
>
>           It is highly desirable [RFC7364  <https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Frfc7364&data=02%7C01%7Clinda.dunbar%40futurewei.com%7C0617f0846cf54f55c0f108d7d122e635%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637207820158976688&sdata=tmD2c1OWRLXfzxnfJ4eG0NU8yfmv2ZMbv7ZJmr4MPZ0%3D&reserved=0>] to allow
>
>           VMs to be moved dynamically (live, hot, or cold move) from one
>
>           server to another for dynamic load balancing or optimized work
>
>           distribution.
>
>
>     In contrast, warm standby does not ever release the 'Old'
>     processing resources, so it cannot be used for dynamically
>     balancing load and optimizing work distribution.
>
>     The following gives the impression that warm 'mobility' is on a
>     spectrum between hot and cold VM mobility:
>
>           The larger the
>
>           duration, the less warm (and hence cold) the Warm VM mobility
>
>           option becomes.
>
>     [Linda] are you satisfied with the following change?
>
>     The Warm VM mobility refers the backup entities receive backup
>     information at more frequent intervals.  The duration of the
>     interval determines the effectiveness (or benefit) of Warm VM
>     mobility.  The larger the duration, the less effective the Warm VM
>     mobility option becomes.
>
>
> [BB] The problem here is a lot deeper than can be fixed with a few 
> word changes.
>
>
>     Warm standby is on a different spectrum to hot and cold mobility.
>     But both hot and cold mobility involve one volley of messages. The
>     only difference is whether processing is stopped or not. Repeating
>     messages is not part way between one message and one message.
>     Regularly repeating messages is not part way between leaving a
>     process running and stopping it.
>
>     [Linda] Agree with you. But this document doesn’t cover “Warm
>     Standby”.
>
>
>     This is still muddle-headed thinking - about redundancy, not
>     mobility. I'm not saying redundancy is not important - it's
>     extremely important. I'm just saying it's out of scope for a VM
>     mobility draft.
>
>         #. Please adopt different terminology than "source NVE" and
>         "destination NVE", which are really poor choices of terms for
>         an intermediate node. See detailed comments. Why not use "old
>         NVE" and "new NVE", which is what you mean?
>
>     [Linda] There is no reference of “source NVE” nor “destination
>     NVE” in the 07 version.
>
>
> [BB2] The sentences starting with '#' are copies of my original review 
> comments (as explained at the start of my email). This one was 
> addressed in your updated drafts, which is why I said '[ADDRESSED]' 
> right below it. And thanked you for addressing it.
>
>
>     [*ADDRESSED*] Thank you
>
>         #. Applicability is fairly clearly outlined, but it is not
>         clear whether hosts corresponding with the mobile VMs are part
>         of the same controlled environment or on the uncontrolled
>         public Internet. See detailed comments.
>
>
>     [*NOT PROPERLY ADDRESSED*]
>
>     [BB] The introduction now contains the useful scoping sentence:
>
>           There are
>
>           communication among tasks belonging to one tenant and
>
>           communication among tasks belonging to different tenants or with
>
>           external entities.
>
>
>     However, AFAICT, the draft still does not address the case where
>     an internal entity moves but it needs to continue to communicate
>     with an external entity that is not controlled by (or even aware
>     of) the NVA.
>
>     [Linda] the behavior on how the Old NVE needs to tunnel packets to
>     the New NVE applies to both external traffic and internal traffic.
>
>
> [BB2] But, by definition, an external entity is not aware of an NVA 
> and there's no reason to assume it has any logic to communicate with 
> an NVA.
>
>
>     A system of tasks within a controlled environment all talking with
>     each other would be like Schroedinger's cat in a box - a quaint
>     thought experiment but not useful. The outside world has to be
>     able to continually give input (requests, data, events, code, etc)
>     and get output (responses, transformed data, notifications, etc).
>     So a VM mobility solution cannot just separate off the outside
>     world as if that's a different problem that is not in scope.
>
>     It's not difficult to do this, but it surely has to be done.
>
>
>
>         #. Section 4.2.1 on L3 VM mobility reads like some potential
>         half-thought-through ideas on how to solve L3 mobility, rather
>         than current practice, let alone best current practice. Either
>         current practice should be described instead, or the scope of
>         the draft should be narrowed solely to L2 VM mobility. See
>         detailed comments.
>
>
>     [*NOT ADDRESSED*]
>
>     [BB] None of the inadequate text in this section has been altered
>     (except terminology find-and-replace that happened to hit words in
>     this section).
>
>     The draft still doesn't deal with the reality of where layer-4
>     connection state is held (in the end applications and the
>     transport stack under them). The authors seem to believe that
>     network elements can close or pause Layer-4 connections. For this,
>     applications have to be built with logic to handle IP address
>     migration. But the scope of this draft is multi-tenant DCs, where
>     the DC infrastructure has no knowledge of which applications each
>     tenant might be using.
>
>     My comments all still apply, and can still be found quoted way
>     down this email (find text: "#. L3 Mobility").
>
>
>
>     For useful tutorial on how TCP responds to ICMP destination
>     unreachable messages (defined as soft errors), and the dilemmas
>     surrounding how TCP should respond, see RFC5461 "TCP's Reaction to
>     Soft Errors".
>     It's probably also worth reading RFC6069 "Making TCP More Robust
>     to Long Connectivity Disruptions (TCP-LCD)".
>     Other transport protocols (e.g. SCTP, QUIC/UDP, RTP/UDP, etc) face
>     similar dilemmas.
>
>     [Linda] Layer 4 connection state handling is out of the scope of
>     NVo3. A separate draft can be written in the Transport Area to
>     deal with Layer Connection state Handling.
>
>
> [BB2] Thank you for finally admitting the parts of this draft about L3 
> migration are a fantasy.
>
> When the L3 parts of the draft talk about using ICMP messages to stop 
> connections or pause connections, it needs to be understood that a 
> connection in TCP/IP /is/ the state at layer 4. The relevant Layer 4 
> connection state /is/ the IP address of its peer that the end systems 
> holds. If you want to avoid more and more tunnels; if you want to 
> prevent IP address space fragmentation, you have to either change that 
> state (the IP address) that is held at layer 4, or make it somehow 
> reference another IP address.
>
> There is no mechanism in this draft to change the IP address that is 
> written into packets to get them from the sender to the receiving end. 
> If dealing with connection state is out of scope, and you don't have 
> any other mechanism, the only outcome is continually more tunnels or 
> continually more address fragmentation.
>
> There are ways to solve this problem, e.g. by adding a layer of 
> abstraction so that the IP addresses held in the L4 connection state 
> are identifiers but not locators. Solutions like HIP, LISP, etc. take 
> this approach. But it's not sufficient to not solve this problem at 
> all, and instead invent a fantasy solution that has no relation to how 
> the TCP/IP architecture works, then say that it would have worked, if 
> only the transport area had written a draft that solved the VM 
> mobility problem for us.
>
>
>         # The VM's file system is described as state that moves with
>         the VM (S.6), but VM mobility solutions often move the VM but
>         stitch it back to its (unmoved) storage. Conversely, the
>         storage can also move independent of the VM.
>
>     [*ADDRESSED*]
>
>     [BB] Thank you.
>
>
>         #. The draft omits some of the security, transport and
>         management aspects of VM mobility. See detailed comments.
>
>
>     [*NOT ADDRESSED*]
>
>     [BB] The Security Considerations section is unchanged. It still
>     only refers to previously known security issues with overlays in
>     general, and does not discuss security vulnerabilities specific to
>     VM mobility. In particular the need for the transport to recheck
>     for address spoofing after each address change, which was
>     identified in my review, which can still be found quoted below
>     under "#. Gaps".
>
>     [Linda] the Security section has the following statement:
>
>     In Layer-3 based overlay data center networks, the problem of
>     address spoofing may arise.  An NVE may have untrusted tasks attached.
>
>
> [BB2] Yes, I know the Security Considerations section says that. And 
> it said that at draft-04 as well. You don't seem to appreciate that I 
> spent the whole of my Sunday afternoon and Monday morning reading and 
> checking the latest version and refreshing my memory to establish 
> whether anything has changed since -04 to address my review comments. 
> It hasn't. The Security Considerations section in -07 still only 
> refers to known security issues with overlays in general.
>
> With VM mobility, the specific /new/ security concern is that a L3 
> address change requires address spoofing to be *re*checked before the 
> move can be considered secure again. The original 
> anti-address-spoofing check was done e2e (that's one purpose of the 
> transport layer handshake). So somehow, a VM mobility solution has to 
> trigger the transport layer to initiate another handshake (which is 
> not something transport protocols are designed to do). Unless there is 
> a solution to this problem, there is no solution to L3 VM mobility.
>
>
>     There is still no mention of the impact of the additional delay /
>     latency, during a mobility event.
>
>     [Linda] that is beyond the scope of this document
>
>
> [BB] To quote the intro, "This document is intended for describing the 
> solutions and the impact of moving VMs ..."
>
>
>     There also is still no mention of statistics gathering, which
>     would be needed to be able to make decisions on when to migrate
>     VMs. But I guess the decision on when to migrate can be ruled to
>     be at a higher scope than this draft.
>
>     [Linda] that is VM manager’s job, out of the scope of NVO3 WG and
>     out of scope of this document.
>
>
>         #. The draft reads as if different sections have been written
>         by different authors and no-one has edited the whole to give
>         it a coherent structure, or to ensure consistency (both
>         technical and editorial) between the parts. See detailed comments.
>
>     [Linda] the 07 version should have fixed the problem.
>
>
> [BB] Of the 5 main problems I points out (listed below), only the 2 
> easy ones were addressed.
>
>
>     [*MOSTLY NOT ADDRESSED*]
>
>     [BB] I made a number of points to help improve the structure and
>     comprehensibility. Two easy 'find-and-replace' ones have been
>     dealt with, but the three that require more than editorial
>     knowledge have not:
>
>      1. [ADDRESSED] VM/task was being used in place of L2/L3. This has
>         been taken on board. Thanks.
>      2. [NOT ADDRESSED] Signposting of where sub-cases start and end
>         in S.4.1
>      3. [NOT ADDRESSED] Indecision over whether packets are silently
>         dropped, dropped with an ICMP message, forwarded or tunnelled.
>      4. [NOT ADDRESSED] The order in which the various stages of
>         mobility occur was jumbled. Some stages have been ruled out of
>         scope, but they are still mentioned in jumbled order.
>      5. [ADDRESSED] Replace hypervisor with NVE. Thanks.
>
>
>         #. The quality of the English grammar does not allow a
>         reviewer to concentrate on the technical aspects rather than
>         the English. It would have been useful if one of the
>         English-speaking co-authors had improved the English before
>         submission for review. See detailed comments.
>
>
>     [*ADDRESSED*] Thanks.
>
>     ==================
>     [BB] New problem
>
>     Whilst checking over -07, I noticed that the definitions of task,
>     workload and VM are now all interchangeable.
>
>            Tasks:  Task is a program instantiated or running on a virtual
>
>                     machine or container.  Tasks in virtual machines or
>
>                     containers can be migrated from one server to another.
>
>                     We use task, workload and virtual machine
>
>                     interchangeably in this document.
>
>
>     Then in 4.2:
>
>           Even though the term VM and Task are used interchangeably in this
>
>           document, the term Task is used in the context of Layer-3
>
>           migration mainly to have slight emphasis on the moving an entity
>
>           (Task) that is instantiated on a VM or a container.
>
>
>     The correct way to deal with confusion between different concepts
>     is not just to say "Well, if you squint up your eyes, all words
>     mean roughly the same thing really."
>
>
> Regards
>
>
>
>
> Bob
>
>
>
>     Bob
>
>     On 24/02/2020 13:10, Bocci, Matthew (Nokia - GB) wrote:
>
>         Hi Bob, Authors
>
>         I am the document shepherd for this draft. It has now been
>         updated to v07 following the shepherd’s review and WG last call.
>
>         Please can you let me know where we are with addressing the
>         comments in this review?
>
>         Thanks
>
>         Matthew
>
>         *From: *Bob Briscoe <ietf@bobbriscoe.net>
>         <mailto:ietf@bobbriscoe.net>
>         *Date: *Friday, 21 September 2018 at 10:34
>         *To: *"sarikaya@ieee.org"
>         <mailto:sarikaya@ieee.org><sarikaya@ieee.org>
>         <mailto:sarikaya@ieee.org>
>         *Cc: *"tsv-art@ietf.org"
>         <mailto:tsv-art@ietf.org><tsv-art@ietf.org>
>         <mailto:tsv-art@ietf.org>, NVO3 <nvo3@ietf.org>
>         <mailto:nvo3@ietf.org>, IETF <ietf@ietf.org>
>         <mailto:ietf@ietf.org>, "draft-ietf-nvo3-vmm.all@ietf.org"
>         <mailto:draft-ietf-nvo3-vmm.all@ietf.org><draft-ietf-nvo3-vmm.all@ietf.org>
>         <mailto:draft-ietf-nvo3-vmm.all@ietf.org>
>         *Subject: *Re: [nvo3] [Tsv-art] Tsvart last call review of
>         draft-ietf-nvo3-vmm-04
>         *Resent from: *<alias-bounces@ietf.org>
>         <mailto:alias-bounces@ietf.org>
>         *Resent to: *<sarikaya@ieee.org> <mailto:sarikaya@ieee.org>,
>         Linda Dunbar <Linda.dunbar@huawei.com>
>         <mailto:Linda.dunbar@huawei.com>, <vumip1@gmail.com>
>         <mailto:vumip1@gmail.com>, <tom@herbertland.com>
>         <mailto:tom@herbertland.com>, <sadikshi@cisco.com>
>         <mailto:sadikshi@cisco.com>, <matthew.bocci@nokia.com>
>         <mailto:matthew.bocci@nokia.com>, Sam Aldrin
>         <aldrin.ietf@gmail.com> <mailto:aldrin.ietf@gmail.com>, Yizhou
>         Li <liyizhou@huawei.com> <mailto:liyizhou@huawei.com>, MARTIN
>         VIGOUREUX <martin.vigoureux@nokia.com>
>         <mailto:martin.vigoureux@nokia.com>, Deborah Brungard
>         <db3546@att.com> <mailto:db3546@att.com>,
>         <aretana.ietf@gmail.com> <mailto:aretana.ietf@gmail.com>,
>         Matthew Bocci <matthew.bocci@nokia.com>
>         <mailto:matthew.bocci@nokia.com>
>         *Resent date: *Friday, 21 September 2018 at 10:34
>
>         Behcet,
>
>         Linda made load of responses to my review, some of which I
>         disagree with so I would like to respond to them. I need
>         responses to those two questions first though, 'cos everything
>         else depends on those.
>
>
>         Bob
>
>         On 20/09/18 15:30, Behcet Sarikaya wrote:
>
>             Dear Bob,
>
>             On Wed, Sep 19, 2018 at 9:53 AM Bob Briscoe
>             <ietf@bobbriscoe.net <mailto:ietf@bobbriscoe.net>> wrote:
>
>                 Behcet,
>
>                 I would like to make significant responses to many of
>                 Linda's responses, but until we get answers to the two
>                 pre-requisite questions I've given, I can't be sure
>                 how to respond.
>
>                 So rather than promising a new version with no prior
>                 discussion, I believe it would be much more fruitful
>                 to engage in this conversation. I'm trying to help.
>
>             You already made a detailed review.
>
>             Your two points are clarifications from your detailed review.
>
>             When I said we will revise I meant we  will revise based
>             on your detailed review.
>
>             After we post our revision you can do what ever you wish.
>
>             Sincerely,
>
>             Behcet
>
>                 Cheers
>
>
>                 Bob
>
>                 On 19/09/18 15:46, Behcet Sarikaya wrote:
>
>                     Hi Bob,
>
>                     Thank you for your comments.
>
>                     The authors are currently discussing your points
>                     and we will come up with a revision soon after the
>                     discussions are over.
>
>                     Regards,
>
>                     Behcet
>
>                     On Tue, Sep 18, 2018 at 6:03 PM Bob Briscoe
>                     <ietf@bobbriscoe.net <mailto:ietf@bobbriscoe.net>>
>                     wrote:
>
>                         Linda,
>
>                         Until we can all understand the answers to the
>                         following two questions, I don't think we can
>                         discuss what track this draft ought to be on,
>                         let alone move on to your responses to all my
>                         other points.
>
>                         1/ Applicability
>
>                         You say this draft solely applies to
>                         connections with both ends within the
>                         controlled DC environment. But the draft says
>                         it's about multi-tenant DCs. Are there any
>                         multi-tenant DCs that restrict all VMs to only
>                         communicate with other VMs within the same
>                         controlled DC environment?
>
>                         2/ Purpose of publishing as an RFC
>
>                         When I said:
>
>                             #. The introduction does not say what the
>                             purpose of publishing this draft is.
>
>                         you responded:
>
>                             [Linda] The first paragraph on Page 3 has
>                             the description why VM Mobility is needed.
>
>
>                         Whether VM Mobility is needed was not my
>                         question. My question was what is the purpose
>                         of the IETF publishing an RFC about VM
>                         Mobility? And particularly, what is /this/ RFC
>                         intended to achieve?
>
>                         Are the authors trying to argue for a
>                         particular approach vs. others? Are you trying
>                         to write a tutorial? Are you trying to give
>                         the pros and cons of different approaches? Are
>                         you trying to give advice on good practice
>                         (with the implication that alternative
>                         practices are less good)? Are you trying to
>                         clarify ideas by writing them down? Are you
>                         trying to outline the implications of VM
>                         Mobility for other protocols being developed
>                         within the NVO WG?
>
>
>
>
>                         Bob
>
>                         On 10/09/18 19:16, Linda Dunbar wrote:
>
>                             Bob,
>
>                             Thank you very much for reviewing the
>                             draft and provided in-depth comments. I am
>                             very sorry for the delayed response due to
>                             traveling.
>
>                             Replies to your comments are inserted
>                             below marked by [Linda]:
>
>                             -----Original Message-----
>                             From: Bob Briscoe
>                             [mailto:ietf@bobbriscoe.net]
>                             Sent: Monday, September 03, 2018 9:45 PM
>                             To: tsv-art@ietf.org <mailto:tsv-art@ietf.org>
>                             Cc: nvo3@ietf.org <mailto:nvo3@ietf.org>;
>                             ietf@ietf.org <mailto:ietf@ietf..org>;
>                             draft-ietf-nvo3-vmm.all@ietf.org
>                             <mailto:draft-ietf-nvo3-vmm.all@ietf.org>
>                             Subject: Tsvart last call review of
>                             draft-ietf-nvo3-vmm-04
>
>                             Reviewer: Bob Briscoe
>
>                             Review result: Not Ready
>
>                             I have been selected as the Transport
>                             Directorate reviewer for this draft. The
>                             Transport Directorate seeks to review all
>                             transport or transport-related drafts as
>                             they pass through IETF last call and IESG
>                             review, and sometimes on special request.
>                             The purpose of the review is to provide
>                             assistance to the Transport ADs. For more
>                             information about the Transport
>                             Directorate Reviews and the Transport Area
>                             Review Team, please see
>                             https://trac..ietf.org/trac/tsv/wiki/TSV-Directorate-Reviews
>                             <https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftrac.ietf.org%2Ftrac%2Ftsv%2Fwiki%2FTSV-Directorate-Reviews&data=02%7C01%7Clinda.dunbar%40futurewei.com%7C0617f0846cf54f55c0f108d7d122e635%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637207820158976688&sdata=ZW9couzD%2FGV7%2BhoMxgmDCDHinKygCsQwL%2BBXL%2Bkqp%2FA%3D&reserved=0>
>
>                             In this case, very very few of the review
>                             comments relate to transport issues,
>                             although the greatest issue concerns a
>                             desire that the network could pause or
>                             stop connections during L3 VM Mobility,
>                             which is certainly a transport issue.
>
>                             [Linda] There is “Hot Migration” with
>                             transport service continuing, and there is
>                             a “Cold Migration”, which is a common
>                             practice in many data centers, which stop
>                             the task running on the old place and move
>                             to the new place before restart as
>                             described in the Task Migration.
>
>                             Is it helpful to add this description to
>                             the draft?
>
>                             ==Summary==
>
>                             The technical aspects of the draft
>                             concerning L2 VM mobility (within a
>                             subnet) seem sound. However, this is only
>                             part of the draft, which has the following
>
>                             issues:
>
>                             #. The introduction does not say what the
>                             purpose of publishing this draft is.
>
>                             It seems that, rather than describing a
>                             specific protocol or protocols, it intends
>                             to describe the overall system procedure
>                             that would typically be used in DCs for VM
>                             mobility. It is tagged as a BCP, but it
>                             does not say who needs this BCP, why it is
>                             useful for the IETF to publish this BCP,
>                             how wide the authors' knowledge is of
>                             current practice (given DCs are private),
>                             or why this is a BCP rather than a
>                             protocol spec.
>
>                             [Linda] The first paragraph on Page 3 has
>                             the description why VM Mobility is needed.
>                             Is it helpful to move this paragraph to
>                             the beginning of the Introduction Section?
>
>                             /“Virtualization which is being used in
>                             almost all of today’s data/
>
>                             /centers enables many virtual machines to
>                             run on a single physical/
>
>                             /computer or compute server. Virtual
>                             machines (VM) need hypervisor/
>
>                             /running on the physical compute server to
>                             provide them shared/
>
>                             /processor/memory/storage. Network
>                             connectivity is provided by the/
>
>                             /network virtualization edge (NVE)
>                             [RFC8014]. Being able to move VMs/
>
>                             /dynamically, or live migration, from one
>                             server to another allows for/
>
>                             /dynamic load balancing or work
>                             distribution and thus it is a highly/
>
>                             /desirable feature [RFC7364].”/
>
>                             The draft starts out (S.3) as if it
>                             intends to say what a good VM Mobility
>                             protocol should or shouldn't do, but the
>                             rest of the document doesn't give any
>                             reasoning for these recommendations, it
>                             just asserts what appears to be one view
>                             of how a whole VM Mobility system works,
>                             sometimes referring to one example
>                             protocol RFC for a component part, but
>                             more often with no references or details.
>
>                             [Linda] Is it helpful to move the
>                             paragraph above to the beginning of the
>                             Introduction Section? So that audience is
>                             aware of why VM Mobility is needed. And
>                             then follow up with what a good VM
>                             Mobility protocol should or shouldn't do?
>
>                             #. It does not seem as if the NVO WG has
>                             discussed the purpose of using normative
>                             text in this draft. See detailed comments.
>
>                             [Linda] The “Intended status” of the draft
>                             is “Best Current Practice”. So all the
>                             text are not “normative”. Is it Okay?
>
>                             #. The draft silently slips back and forth
>                             between VM mobility and VM redundancy,
>                             without recognizing the differences. See
>                             detailed comments.
>
>                             [Linda] There is only one usage of
>                             “redundancy” in the entire document, used
>                             under the context of “Hot standby option”,
>                             indicating  the “redundancy” of “the VMs
>                             in both primary and secondary domains have
>                             identical information and can provide
>                             services simultaneously as in load-share
>                             mode of operation” being expensive.
>
>                             #. Please adopt different terminology than
>                             "source NVE" and "destination NVE", which
>                             are really poor choices of terms for an
>                             intermediate node. See detailed comments.
>                             Why not use "old NVE" and "new NVE", which
>                             is what you mean?
>
>                             [Linda] Thanks for the suggestion. We will
>                             change to “Old NVE”, and “new NVE”.
>
>                             #. Applicability is fairly clearly
>                             outlined, but it is not clear whether
>                             hosts corresponding with the mobile VMs
>                             are part of the same controlled
>                             environment or on the uncontrolled public
>                             Internet. See detailed comments.
>
>                             [Linda] “Hosts” are the App running on the
>                             VM. It is the under the same controlled
>                             environment. Not on uncontrolled public
>                             internet.
>
>                             #. Section 4.2.1 on L3 VM mobility reads
>                             like some potential half-thought-through
>                             ideas on how to solve L3 mobility, rather
>                             than current practice, let alone best
>                             current practice. Either current practice
>                             should be described instead, or the scope
>                             of the draft should be narrowed solely to
>                             L2 VM mobility. See detailed comments.
>
>                             [Linda] This is refereeing to “Cold
>                             Migration”, which is a common practice in
>                             many data centers.
>
>                             # The VM's file system is described as
>                             state that moves with the VM (S.6), but VM
>                             mobility solutions often move the VM but
>                             stitch it back to its (unmoved) storage.
>                             Conversely, the storage can also move
>                             independent of the VM.
>
>                             [Linda] It depends. When a VM move to a
>                             different zone, the storage/file can
>                             becomes inaccessible.
>
>                             #. The draft omits some of the security,
>                             transport and management aspects of VM
>                             mobility. See detailed comments.
>
>                             [Linda] Can you provide some text?
>
>                             #. The draft reads as if different
>                             sections have been written by different
>                             authors and no-one has edited the whole to
>                             give it a coherent structure, or to ensure
>                             consistency (both technical and editorial)
>                             between the parts. See detailed comments.
>
>                             [Linda] we can improve.
>
>                             #. The quality of the English grammar does
>                             not allow a reviewer to concentrate on the
>                             technical aspects rather than the English.
>                             It would have been useful if one of the
>                             English-speaking co-authors had improved
>                             the English before submission for review.
>                             See detailed comments.
>
>                             [Linda] can you help?  Becoming a
>                             co-author to improve?
>
>                             ==Detailed Comments==
>
>                             ===#. Normative statements===
>
>                             In the body of the document, there is just
>                             one occurrence of normative text (actually
>                             two "MUST"s, but both state a common
>                             requirement - just written separately for
>                             IPv4 and IPv6). This merely serves to
>                             imply that everything else the document
>                             says is less important or optional, which
>                             was probably not the intention.
>
>                             [Linda] The goal is to indicate any
>                             solution in moving the VM “MUST” follow
>                             this rule. They make sense, aren’t they?
>
>                             At the start there is a requirements
>                             section, which states what a VM Mobility
>                             protocol "SHOULD" or "SHOULD NOT" do. I
>                             think this is intended as a set of goals
>                             for the rest of the document. If so, these
>                             "SHOULDs" are not intended to apply to
>                             implementations, so they ought not to be
>                             capitalized.
>
>                             [Linda] okay, will change.
>
>                             The first requirement, "Data center
>                             network SHOULD support virtual machine
>                             mobility in IPv6", is written as a
>                             requirement on all DC networks, not on
>                             implementations. I assume this was
>                             intended to read as "Data center network
>                             virtual machine mobility protocols SHOULD
>                             support IPv6". Even then, it doesn't
>                             really add anything to say VM mobility
>                             should support v6 and it should support
>                             v4. A L2 solution won't. While
>                             undoubtedly, a L3 solution will at least
>                             support one of them.
>
>                             [Linda]Agree. Will change it to “Data
>                             center that support IPv6 address should …”
>
>                             I'm not sure that 'protocol' is the right
>                             word anyway; I think 'VM Mobility
>                             procedure' would be a better phrase,
>                             because it includes steps such as
>                             suspending the VM, which is more than a
>                             protocol.
>
>                             [Linda] yes. Will change to “Procedure”.
>
>                             The requirement "Virtual machine mobility
>                             protocol MAY support host routes to
>                             accomplish virtualization", is not
>                             followed up at all in the rest of the draft.
>
>                             Even if this requirement stays, the last 3
>                             words should be deleted.
>
>                             [Linda] will change to “Host Route can be
>                             used to support the Virtual Machine
>                             Mobility Procedure.”
>
>                             By the end of the draft, the solution
>                             falls far short of the most relevant
>                             "Requirements" anyway, so one assumes the
>                             title of the section ought to have been
>                             "Goals". Specifically, even in the simpler
>                             case of L2 VM mobility, S.4.1 says that
>                             triangular routing and tunnelling persist
>                             "until a neighbour cache entry times out".
>                             A cache timeout is about 10 orders of
>                             magnitude longer than the requirement to
>                             only persist "while handling packets in
>                             flight", which would be a few milliseconds
>                             at most (the time for packets to clear the
>                             network that were already launched into
>                             flight when the old VM stopped).
>
>                             Whatever, it would be preferable for the
>                             draft to give rationale for these
>                             requirements, rather than just assert
>                             them. This would help to shed light on the
>                             merits of the different trade offs that
>                             solutions choose.
>
>                             [Linda] Agree, will add.
>
>                             ===#. Mobility vs. Redundancy===
>
>                             Redundancy and mobility have a lot of
>                             similarities, but they have different
>                             goals. With mobility, it is necessary to
>                             know the exact instant when one set of
>                             state is identical to the other so it can
>                             hand over. With redundancy, the aim is to
>                             keep two (or more) sets of state evolving
>                             through the same sequence of changes, but
>                             there is no need to know the point at
>                             which one is the same as the other was at
>                             a certain point.
>
>                             [Linda] Agree with what you said. There is
>                             only one usage of “redundancy” in the
>                             entire document, used under the context of
>                             “Hot standby option”, indicating  the
>                             “redundancy” of  “the VMs in both primary
>                             and secondary domains have identical
>                             information and can provide services
>                             simultaneously as in load-share mode of
>                             operation” being expensive.
>
>                             The draft slips from mobility to
>                             resilience in the following places:
>
>                             * S.2. Terminology: Warm VM Mobility is
>                             defined without any ending, as if it is
>                             permanent replication. * S.7. "Handling of
>                             Hot, Warm and Cold Virtual Machine
>                             Mobility" is actually all about
>                             redundancy, and doesn't address mobility
>                             explicitly.
>
>                             [Linda] Will add the definition “Hot
>                             Migration”, “cold migration”, and “warm
>                             migration”.
>
>                             ===#. Terminology===
>
>                             Packets run from the source at A to the
>                             destination at B via NVE1, then via NVE2.
>                             Please don't call NVE1 and NVE2 the source
>                             NVE and the destination NVE.
>
>                             In future, no-one will thank you for the
>                             apparent contradictions when they
>                             continually stumble over phrases like this
>                             one in S.4.1: "...send their packets to
>                             the source NVE"..
>
>                             The term "packets in flight" is used
>                             incorrectly to refer to all the packets
>                             sent to the old NVE after the VM has
>                             moved, even if they were launched into
>                             flight long after the old VM stopped
>                             receiving packets.
>
>                             [Linda] thank for the comments. Will change.
>
>                             BTW, I think s/before/after/ in: "that
>                             have old ARP or neighbor cache entry
>                             before VM or task migration".
>
>                             I think: s/IP-based VM mobility/L3 VM
>                             mobility/ throughout, because "based"
>
>                             sounds (to me) like the mobility control
>                             protocol is over (i.e. based on) IP.
>
>                             ===#. Applicability===
>
>                             In section 4.2 it says that the protocol
>                             mostly used as the IP based task migration
>                             protocol is ILA. This implies that all
>                             hosts corresponding with the mobile VMs
>                             are either part of the same controlled
>                             environment, or they are proxied via nodes
>                             that are part of the same controlled
>                             environment (I only have passing knowledge
>                             of ILA, but I understand that it depends
>                             on ILA routers on the path). If I am
>                             correct, this aspect of scope needs to be
>                             made clear from the start.
>
>                             Also under the heading of applicabiliy,
>                             the sentence "Since migrations should be
>                             relatively rare events" appears very late
>                             in the document (S.4.2.1). The assumed
>                             level of churn ought to be stated nearer
>                             the start.
>
>                             [Linda] yes, under the same controlled
>                             environment.
>
>                             ===#. L3 Mobility===
>
>                             L2 VM mobility is independent of the
>                             application, because resolution of L2
>                             mappings is delegated to the stack. In
>                             contrast, L3 VM mobility is only feasible
>                             under certain conditions, because an
>                             application needs an IP address to open a
>                             socket (resolution of DNS names is not
>                             delegated to the stack, and apps can use
>                             IP addresses directly anyway).
>
>                             Examples of the 'certain conditions':
>
>                             a) /All/ applications used in the whole DC
>                             load balancing scheme contain IP address
>                             migration logic for /all/ their connections;
>                             b) VMs running solely applications that
>                             support IP address migration register this
>                             fact with the NVA, and it only select such
>                             VMs for mobility.
>                             c) An abstraction is layered over /all/
>                             the IP addresses exposed to applications
>                             (at both ends) so that the IP addresses
>                             that applications use are solely
>                             identifiers (e.g. ILA, LISP, HIP), not
>                             also locators.
>
>                             The introduction says the draft is about
>                             VM mobility in a multi-tenant DC, so the
>                             DC admin will not know the range of
>                             applications being used. This excludes
>                             condition (a) above. When the draft says
>                             "...if all applications running are known
>                             to handle this gracefully...", it doesn't
>                             quantify just how restrictive this
>                             condition is, and it gives no explanation
>                             of how this knowledge might be 'known' or
>                             which function within the system 'knows' it.
>
>                             S.4.2.1 contains what seems like plenty of
>                             arm-waving.
>
>                             * "TCP connections could be automatically
>                             closed in the network stack during a
>                             migration event."
>
>                                     o There is no TCP connection state
>                             in the network stack.
>
>                                     o Even if the network starts to
>                             drop every packet, the TCP connection
>
>                             state persists in the end-points for a
>                             duration of the order of 30-90
>
>                             minutes (OS-dependent) before TCP deems
>                             the connection is broken.
>                                    o Other transport protocols have
>                             similar designs (including the app-layer
>
>                             of protocols over UDP).
>
>                             * "More involved approach to connection
>                             migration":
>
>                                     o pausing the connection [does
>                             this refer to an actual feature of any
>
>                             L4 protocol?]
>                                     o packaging connection state and
>                             sending to target [does
>
>                             this assume logic written into the
>                             application, or is this assuming the
>
>                             stack handles this and the app is
>                             restricted to using some form of
>
>                             separate identifier/locator addresses?]
>                                     o instantiating connection state
>                             in the peer stack [ditto?].
>
>                             There's some arm-waving in S.7 too:
>
>                               "Cold Virtual Machine mobility is
>                             facilitated by the VM initially
>
>                             sending an ARP or Neighbor Discovery
>                             message at the destination NVE
>
>                                but the source NVE not receiving any
>                             packets inflight."
>
>                                [How is it arranged for the source NVE
>                             not to receive any packets in flight?]
>
>                             And in S.7:
>
>                               "In hot
>
>                             standby option, regarding TCP connections,
>                             one option is to start
>
>                                with and maintain TCP connections to
>                             two different VMs at the same
>
>                                time."
>
>                                [This sounds like resilience logic has
>                             been written into the application,
>
>                                which would be a special case but not
>                             something VM mobility infrastructure
>
>                                could depend on.]
>
>                             [Linda] will add.
>
>                             ===#. Gaps===
>
>                             #. Security Considerations: repeats issues
>                             in other drafts that are not specific to
>                             mobility, but it does not mention any
>                             security issues specifically due to VM
>                             mobility. It says that address spoofing
>                             may arise in a DC (sort-of implying it is
>                             worse than in non-DC environments, but not
>                             saying why). The handshake at the start of
>                             a connection (e.g. TCP, SCTP, QUIC) checks
>                             for source address spoofing. So L3 VM
>                             mobility would be more vulnerable to
>                             source address spoofing in cases where the
>                             mobile VM was the connection initiator and
>                             there was not a new handshake after the
>                             move. However, this draft does not contain
>                             any detailed mobility protocols, so it is
>                             not possible to identify any specific
>                             security flaws.
>
>                             #. Transport Issues: Effect of delay on
>                             the transport: Cold mobility introduces
>                             significant delay, and other forms less,
>                             but still some delay. It should be pointed
>                             out that some applications (e.g.
>                             real-time) will therefore not be useful if
>                             subjected to VM mobility. Similarly, even
>                             a short period of delay will drive most
>                             congestion controls to severely reduce
>                             throughput. These points might be
>                             self-evident, but perhaps they should be
>                             stated explicitly.
>
>                             BTW, in the L3 VM mobility case, the draft
>                             often refers to TCP connections, but the
>                             address bindings of any transport
>                             protocols would have to be migrated due to
>                             VM mobility (e.g. SCTP; sequences of
>                             datagrams over UDP; streams over UDP such
>                             as with RTP, QUIC).
>
>                             #. Management Issues: perhaps the draft
>                             ought to recommend statistics gathering
>                             (e.g. time taken, amount of duplicate
>                             data) to aid a DC's future decisions on
>                             the cost-benefit of moving a VM. The
>                             OPSDIR review says a BCP does not /have/
>                             to describe management issues, but this
>                             document seems to describe a whole system
>                             procedure, not just a protocol, which then
>                             surely includes the management plane.
>
>                             [Linda] can you become a co-author and add
>                             those in?
>
>                             ===#. Incoherent Structure===
>
>                             S.4.1. happens to talk about VMs moving,
>                             while S.4.2. happens to talk about tasks
>                             moving, but this is not the distinguishing
>                             aspect of these two sections (anyway, S.2.
>                             says "the draft uses task and VM
>                             interchangeably"): * "4.1 VM Migration" is
>                             about "L2 VM Mobility" so this ought to be
>                             the section heading, *
>
>                             "4.2 Task Migration" is about "L3 VM
>                             Mobility" so this ought to be the section
>                             heading. It would also help not to switch
>                             from VM to task across these sections
>
>                             - it's just a distraction.
>
>                             S.4.1 needs better signposting of where
>                             each sub-case ends (Subsections might be
>                             useful to solve this): * IPv4 * end-user
>                             client * 2 paras starting "All NVEs
>                             communicating with this virtual
>                             machine..." [Not clear that the end-user
>                             case has ended and we have returned to the
>                             general IPv4 case?] * IPv6 [Strictly, it
>                             still hasn't said whether the end-user
>                             client case has ended.] [Also, it doesn't
>                             explain why there is no need for an
>                             end-user client case under IPv6?] Sections
>                             5 & 6 seem to be about either L2 or L3
>                             mobility, whereas Sections 7 &
>
>                             8 seem to be restricted to L2.
>
>                             The draft vacillates over what to do with
>                             packets arriving at the old NVE in the L3
>                             case (see also L3 mobility above): * S4.2
>                             first says packets are dropped, possibly
>                             with an ICMP error message;
>
>                               o then later it says they are silently
>                             dropped;
>
>                               o then in the very next sentence it says
>                             either silently drop them or forward
>
>                               them to the new location
>
>                             * S.5 says they should not be lost, but
>                             instead delivered to the destination
>                             hypervisor
>
>                               o then it describes how they are
>                             tunnelled (which is not the same as
>
>                             "forwarding").
>
>                             The order in which all the stages of
>                             mobilty are given is jumbled up across
>                             sections that also appear in arbitrary
>                             order: * S.5 prepares, establishes uses
>                             then stops a tunnel, but it doesn't say
>                             where the other stages fit between these steps
>
>                                     o When tunneling packets, it talks
>                             about the *migrating* VM not the
>
>                             *migrated* VM, which implies tunnelling
>                             has started before the new VM
>
>                             is running. Does this imply there is a
>                             huge buffer? o It says "Stop
>
>                             Tunneling Packets - When source NVE stops
>                             receiving packets destined
>
>                             to..." but it is never clear when a source
>                             has stopped sending packets
>
>                             to a destination, unless it explicitly
>                             closes the connection (e.g. with
>
>                                     a FIN in the case of TCP). Often
>                             there are long gaps between packets,
>
>                             because many flows are 'thin' (meaning the
>                             application frequently has
>
>                             nothing to send). These gaps can last for
>                             milliseconds, hours or even
>
>                             days without any implication that the
>                             connection has ended.
>
>                             * Then S.6. describes moving state, but
>                             doesn't say that this is not after the
>                             previous tunnelling steps (or where it
>                             fits within those steps). * Then S.7
>                             describes hot, warm and cold mobility, but
>                             doesn't lay out the tunnelling or steps to
>                             move state in each case. * Then S.8 says
>                             it's about VM life-cycle, but just gives
>                             the very first 3 steps for allocation of
>                             resources to a VM, then abruptly ends,
>                             without even starting the VM, let alone
>                             getting to move it.
>
>                             S.5 exhibits another inconsistency by
>                             talking about the hypervisor, not the NVE.
>
>                             ==#. Nits==
>
>                             Nits with the English are too numerous to
>                             mention them all. Below are pointers to
>                             general problems as well as some
>                             individual instances.
>
>                             S.4
>
>                               "Layer 2 and Layer 3 protocols are
>                             described next.  In the following
>
>                             sections, we examine more advanced features."
>
>                             s/following/subsequent/
>
>                             S.4.1
>
>                             Expand WSC, MSC and NVA on first use.
>
>                             s/the VM moves in the same link/the VM
>                             moves in the same subnet/
>
>                             "i.e. end-user clients ask for the same
>                             MAC address upon migration. [...] to
>                             ensure that the same IPv4 address is
>                             assigned to the VM." I think s/IPv4/MAC/
>                             was intended?
>
>                             "  All NVEs communicating with this
>                             virtual machine uses the old ARP
>
>                             entry.  If any VM in those NVEs need to
>                             talk to the new VM in the
>
>                             destination NVE, it uses the old ARP entry."
>
>                             Repetition: these 2 sentences say the
>                             same. (The mistake is also repeated when
>                             these 2 sentences are repeated for IPv6).
>
>                             S.4.2.1
>
>                             s/Push the new mapping to hosts./Push the
>                             new mapping to communicating hosts./
>
>                             S.5.
>
>                             The IPv4/IPv6 pairs of paras for "tunnel
>                             estabilshment" and "tunneling packets"
>
>                             only differ in the words "IPv4"/"IPv6". So
>                             in each case a single para could be given
>                             for IP (irrespective of whether v4 or v6).
>
>                             Thank you very much.
>
>                             Linda Dunbar
>
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Bob Briscoe                               http://bobbriscoe.net/