Re: Comments on draft-ietf-bfd-unaffiliated-echo-08

xiao.min2@zte.com.cn Thu, 28 September 2023 07:03 UTC

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From: xiao.min2@zte.com.cn
To: gregimirsky@gmail.com
Cc: ketant.ietf@gmail.com, rtg-bfd@ietf.org, draft-ietf-bfd-unaffiliated-echo@ietf.org
Subject: Re: Comments on draft-ietf-bfd-unaffiliated-echo-08
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Hi Greg,

Thank you for the reply.
Please see inline with [XM-2]>>>.

Original


From: GregMirsky <gregimirsky@gmail.com>
To: 肖敏10093570;
Cc: ketant.ietf@gmail.com <ketant.ietf@gmail.com>;rtg-bfd@ietf.org <rtg-bfd@ietf.org>;draft-ietf-bfd-unaffiliated-echo@ietf.org <draft-ietf-bfd-unaffiliated-echo@ietf.org>;
Date: 2023年09月28日 05:13
Subject: Re: Comments on draft-ietf-bfd-unaffiliated-echo-08



Hi Xiao Min,thank you for your expedient response. Please find my notes below tagged GIM>>.

Regards,
Greg




On Tue, Sep 26, 2023 at 6:37 PM <xiao.min2@zte.com.cn> wrote:


Hi Greg,

Please see inline.

Original

From: GregMirsky <gregimirsky@gmail.com>
To: Ketan Talaulikar <ketant.ietf@gmail.com>;
Cc: 肖敏10093570;rtg-bfd WG <rtg-bfd@ietf.org>;draft-ietf-bfd-unaffiliated-echo@ietf.org <draft-ietf-bfd-unaffiliated-echo@ietf.org>;
Date: 2023年09月27日 02:21
Subject: Re: Comments on draft-ietf-bfd-unaffiliated-echo-08


Hi Ketan,
Thank you for sharing your interpretation of the introduced text. I agree that your view is in line with how the scope of BFD is defined in RFC 5880:
 protocol intended to detect faults in the bidirectional path between two forwarding engines, including interfaces, data link(s), and to the extent possible the forwarding engines themselves But it is not clear to me how "liveness of a node" is retated to the definition above. I hope thr Authors will clarify that for me.
[XM]>>> In my understanding it's the liveness of the forwarding engine.
Do you expect s/the liveness of a node/the liveness of a node over the specific interface as Ketan clarified?







GIM>>  I think that the Unaffiliated BFD and BFD, in general, do not detect defects on the nodal level. Thus, the "liveness of a node" seems inaccurate, overstretching the scope of BFD as defined in RFC 5880. I suggest referring to the definition of the BFD from RFC 5880 or providing an explanation of how the Unaffiliated BFD extends the defect detection domain up to the nodal scope.
[XM-2]>>> I personally don't think the "liveness of a node" has any technical problem. At the same time, as I understand your comment, you think the liveness of a node is a bigger concept than what can be detected by the BFD Echo or BFD, which also makes sense to me in some extent. To avoid the potential confusion, I propose to change the text as below.
OLD
Note that this method monitors the liveness of a node not including the availability of a specific IP address at that node.¶
NEW
Note that what this method monitors does not include the availability of a specific IP address at the neighboring device.

Cheers,
Xiao Min
¶
Regards,
Greg





Best Regards,
Xiao Min
Regards,Greg




On Tue, Sep 26, 2023, 09:56 Ketan Talaulikar <ketant.ietf@gmail.com> wrote:


Hi Greg,
I would read it as " ... the liveness of a node over the specific interface ..." i.e, the node is reachable and responding over that interface.

Thanks,
Ketan





On Tue, Sep 26, 2023 at 7:16 PM Greg Mirsky <gregimirsky@gmail.com> wrote:



Hi,as I understand it, the update assigns to the Unaffiliated BFD a new functionality, monitoring "the liveness of a node not including the availability of a specific IP address at that node". In my opinion, that raises some questions:
What is "the liveness of a node"?

When referring to the liveness of a node, does it applicable to a single-box system or also to a virtual, distributed, e.g., the one using the CUPS paradigm?

How the liveness of a node is derived from the functionality of a single interface? Is it equally applicable regardless the interface is physical or virtual?

Thank you for your consideration.


Regards,
Greg





On Tue, Sep 26, 2023 at 5:38 AM Ketan Talaulikar <ketant.ietf@gmail.com> wrote:


Thanks Xiao Min - the update looks good and addresses my comments.
Thanks,
Ketan




On Tue, Sep 26, 2023 at 12:58 PM <xiao.min2@zte.com.cn> wrote:


Hi Ketan,

Thank you for the suggested text, very helpful.
I've just posted a new revision that incorporates all your comments. Link as below.
https://datatracker.ietf.org/doc/html/draft-ietf-bfd-unaffiliated-echo-09
 Please see inline with [XM-2]>>>.

Original

From: KetanTalaulikar <ketant.ietf@gmail.com>
To: 肖敏10093570;
Cc: draft-ietf-bfd-unaffiliated-echo@ietf.org <draft-ietf-bfd-unaffiliated-echo@ietf.org>;rtg-bfd@ietf.org <rtg-bfd@ietf.org>;jhaas@pfrc.org <jhaas@pfrc.org>;
Date: 2023年09月25日 15:37
Subject: Re: Comments on draft-ietf-bfd-unaffiliated-echo-08



Hi Xiao Min,
Thanks for your response. Please check inline below for further suggestions.




On Mon, Sep 25, 2023 at 11:41 AM <xiao.min2@zte.com.cn> wrote:


Dear Ketan,

Thanks for your review and thoughtful comments.
Please see inline.

Original

From: KetanTalaulikar <ketant.ietf@gmail.com>
To: draft-ietf-bfd-unaffiliated-echo@ietf.org <draft-ietf-bfd-unaffiliated-echo@ietf.org>;
Cc: rtg-bfd@ietf.org <rtg-bfd@ietf.org>;Jeffrey Haas <jhaas@pfrc.org>;
Date: 2023年09月22日 22:55
Subject: Comments on draft-ietf-bfd-unaffiliated-echo-08


Hello Authors,

Looks like I've missed the WGLC on this document, but nevertheless would like to share the following comments:

Sec 1 of the document says:

Section 5 of [RFC5880] indicates that the payload of an affiliated BFD Echo packet is a local matter and hence its contents are outside the scope of that specification. This document, on the other hand, specifies the contents of the Unaffiliated BFD Echo packet and what to do with them.


However, when I go through the procedures in Section 2, there is no description of the actual construction of the IP packet that A sends out to B - what is the source and destination IP - or MAC addresses for that matter? How is it that B would loop it back? I believe it is important for the document to specify this.
[XM]>>> This document does specify the source and destination IP, through reference to RFC 5881. In section 2 it says
"Regarding the selection of IP address, the rules stated in Section 4 of [RFC5881] are applicable to the encapsulation of an Unaffiliated BFD Echo packet."
In -07 version the rules of RFC 5881 were restated, however in -08 version they're removed by following the suggestion from Greg.







KT> I missed that conversation. One small suggestion so it covers not just IP address but also MAC.

OLD: Regarding the selection of IP address, the rules stated in Section 4 of [RFC5881] are applicable to the encapsulation of an Unaffiliated BFD Echo packet. 

NEW: An Unaffiliated BFD Echo packet follows the same encapsulation rules as for a BFD Echo packet as specified in Section 4 of [RFC5881]. 
[XM-2]>>> Accepted.







Another important part is that normally BFD verifies the bidirectional path, the liveness of the other endpoint, but also validates the presence of a specific IP at that endpoint. Is that still the case when operating in this mode? This question arises since the document talks about liveness to servers - so is it monitoring liveness to the server host or a specific server IP?
[XM]>>> It's monitoring liveness to the server host, not a specific server IP. Also note that the Unaffiliated BFD Echo can be used for multiple use cases, in section 1 it says
"Section 6.2.2 of [BBF-TR-146] describes one use case of the Unaffiliated BFD Echo. Section 2 of [I-D.wang-bfd-one-arm-use-case] describes another use case of the Unaffiliated BFD Echo."







KT> This is OK. I was looking for some text (perhaps in Section 1) that says something on the lines of ... "The Unaffiliated BFD Echo functionality only monitors liveness of the node and does not monitor the availability of a specific IP address at that node." - I believe this is an important distinction from normal BFD operations that needs to be called out. Would you agree?
[XM-2]>>> Some text as you want was added to section 1.





Finally, is it normal or natural to expect server hosts to be able to "loop them back by normal IP forwarding"? Or does it require some additional/special capabilities to be turned ON those hosts as hosts don't do forwarding by default.
[XM]>>> As I know of a deployment, there is no need to turn ON those hosts. At the same time, it's feasible to have such a knob. Propose to add some text as below.
OLD
The method for provisioning device B to loop back BFD Unaffiliated Echo packets is outside the scope of this document.
NEW
There may be a knob to turn on/off the loopback of Unaffiliated BFD Echo packets at device B. The method for provisioning device B to loop back Unaffiliated BFD Echo packets is outside the scope of this document.









KT> This is not quite where I was going. Perhaps something on the following lines?
NEW:
BFD Unaffiliated Echo feature depends on device B performing IP forwarding (actually IP redirect) functionality. While such functionality may normally be expected to be supported on a router, it may not be enabled on a host by default. The method for provisioning device B to loop back BFD Unaffiliated Echo packets is outside the scope of this document.
[XM-2]>>> Accepted. 

Best Regards,
Xiao Min

Thanks,
Ketan






Best Regards,
Xiao Min

It would help if these aspects are clarified in the document.

Thanks,
Ketan



On Thu, Jul 6, 2023 at 7:50 AM <internet-drafts@ietf.org> wrote:


 A New Internet-Draft is available from the on-line Internet-Drafts
 directories. This Internet-Draft is a work item of the Bidirectional
 Forwarding Detection (BFD) WG of the IETF.
 
    Title           : Unaffiliated BFD Echo
    Authors         : Weiqiang Cheng
                      Ruixue Wang
                      Xiao Min
                      Reshad Rahman
                      Raj Chetan Boddireddy
    Filename        : draft-ietf-bfd-unaffiliated-echo-08.txt
    Pages           : 12
    Date            : 2023-07-05
 
 Abstract:
    Bidirectional Forwarding Detection (BFD) is a fault detection
    protocol that can quickly determine a communication failure between
    two forwarding engines.  This document proposes a use of the BFD Echo
    where the local system supports BFD but the neighboring system does
    not support BFD.  BFD Control packet and its processing procedures
    can be executed over the BFD Echo port where the neighboring system
    only loops packets back to the local system.
 
    This document updates RFC 5880.
 
 The IETF datatracker status page for this Internet-Draft is:
 https://datatracker.ietf.org/doc/draft-ietf-bfd-unaffiliated-echo/
 
 There is also an htmlized version available at:
 https://datatracker.ietf.org/doc/html/draft-ietf-bfd-unaffiliated-echo-08
 
 A diff from the previous version is available at:
 https://author-tools.ietf.org/iddiff?url2=draft-ietf-bfd-unaffiliated-echo-08
 
 Internet-Drafts are also available by rsync at rsync.ietf.org::internet-drafts