Re: [bess] WG Last Call for draft-ietf-bess-evpn-inter-subnet-forwarding-03

"Ali Sajassi (sajassi)" <sajassi@cisco.com> Fri, 17 February 2017 22:25 UTC

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From: "Ali Sajassi (sajassi)" <sajassi@cisco.com>
To: "Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net>, Martin Vigoureux <martin.vigoureux@nokia.com>, BESS <bess@ietf.org>
Thread-Topic: [bess] WG Last Call for draft-ietf-bess-evpn-inter-subnet-forwarding-03
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Date: Fri, 17 Feb 2017 22:25:26 +0000
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Subject: Re: [bess] WG Last Call for draft-ietf-bess-evpn-inter-subnet-forwarding-03
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Hi Jeffrey,

Thanks for your comments, please refer inline for my responses ...

On 2/17/17, 10:42 AM, "BESS on behalf of Jeffrey (Zhaohui) Zhang"
<bess-bounces@ietf.org on behalf of zzhang@juniper.net> wrote:

>Hi,
>
>I have the following nits/questions/comments. This email is only about
>the asymmetric section  - I may send another one about symmetric section.
>
>"inter-subnet switching" is confusing. Shouldn't it be "inter-subnet
>routing" instead of "intra-subnet switching"? While it's EVPN aware, it
>still goes through routing first.

The term ³switching² applies to both L2 and L3; whereas, the term
³bridging² applies to only L2 and the term ³routing² applies to only L3.

>
>Isn't requirement R1 covered by R2?

Yup, will remove R1.

>
>   This is an environment where all NVEs to which an EVPN instance could
>   potentially be attached (or moved)
>
>Strike the "(or moved)"?

OK.

>
>>From RFC 7432:
>
>10.1.  Default Gateway
>   ...
>   The IP Address field of the MAC/IP Advertisement route is set to the
>   default gateway IP address for that subnet (e.g., an EVPN instance).
>   For a given subnet (e.g., a VLAN or EVPN instance), the default
>   gateway IP address is the same across all the participant PEs. The
>   inclusion of this IP address enables the receiving PE to check its
>   configured default gateway IP address against the one received in the
>   MAC/IP Advertisement route for that subnet (or EVPN instance), and if
>   there is a discrepancy, then the PE SHOULD notify the operator and
>   log an error message.
>
>This draft:
>
>   2. Each NVE of a given EVPN instance uses its own default gateway IP
>   and MAC addresses, and these addresses are aliased to the same
>   conceptual gateway through the use of the Default Gateway extended
>   community as specified in [EVPN], which is carried in the EVPN MAC
>   Advertisement routes. On each NVE, this default gateway IP/MAC
>   address correspond to the IRB interface connecting the MAC-VRF of
>   that EVI to the corresponding IP-VRF.
>
>The above 2nd model seems to be conflicting with RFC 7432?


Thanks for catching it. The 2nd case is supposed to be ³the same IP
anycast address but different MAC addresses" - ie, the two use cases in
this draft correspond to the two uses cases in section 10.1 of RFC 7432.
So, the new text reads as follow:

³2. Each NVE of a given EVPN instance uses the same anycast default
gateway IP address but its own MAC address. These MAC addresses are
aliased to the same anycast default gateway IP address through the use of
the Default Gateway extended community as specified in [EVPN], which is
carried in the EVPN MAC/IP Advertisement routes. On each NVE, this default
gateway IP address along with its associated MAC addresses correspond to
the IRB interface connecting the MAC-VRF of that EVI to the corresponding
IP-VRF.²
 

>Also, what does "this default gateway" refer to? Each NVE's "own default
>gateway" or "the same conceptual gateway"?

Default gateway with respect to TS¹s as mentioned in the 2nd para of
section 3.1


>Is it that besides their own default gateway, an additional common
>gateway is advertised using that extended community? If so, what's the
>purpose to call those different IP addresses on the IRB interfaces
>"default gateway"? I assume the hosts will be using the common gateway
>address?

This comment should be already addressed by above clarification.

>
>   It is worth noting that if the applications that are running on the
>   TS's are employing or relying on any form of MAC security, then the
>   first model (i.e. using anycast addresses) would be required to
>   ensure that the applications receive traffic from the same source MAC
>   address that they are sending to.
>
>Why is that? As long as an NVE changes the source MAC to the one it sends
>in the ARP reply, it should work even with the 2nd model?

If it changes, yes but if it doesn¹t change it, it creates issue for MAC
security. Modified the paragraph to provide further clarification:

"It is worth noting that if the applications that are running on the TS's
are employing or relying on any form of MAC security, then either the
first model (i.e. using anycast MAC address) should be used to ensure that
the applications receive traffic from the same IRB interface MAC address
that they are sending to, or if the second model is used, then the IRB
interface MAC address MUST be the one used in the initial ARP reply for
that TS."


>
>3.2 Heterogeneous Environment
>
>   .. Even though policies
>   among multiple subnets belonging to same tenant can be simpler,
>
>s/simpler/simple/?

Done.

>
>   ... Therefore, there can be a mixed environment where an NVE
>   performs inter-subnet switching for some EVPN instances and the L3GW
>   for others.
>
>For the above sentence, it helps a lot if the last part reads "and the
>L3GW performs inter-subnet switching for other EVPN instances".

Done.

>
>4.1 Among EVPN NVEs within a DC
>
>   ... It also rewrites the source MAC address with its IRB
>   Interface MAC address.
>
>Need to make it clear that the above mentioned IRB interface is for the
>destination subnet. Same issue in 4.2.

Changed it to:

"It also rewrites the source MAC address with its IRB Interface MAC
address for the destination subnet.²

>
>For section 4.2, the processing on the ingress and egress NVE is no
>different from 4.1; the processing on the ASBRs is vanilla EVPN
>forwarding and not specific to inter-subnet forwarding at all; therefore,
>4.2 is not really needed? Additionally, the section is about "w/o GW",
>yet the text talks about ingress/egress Gateway. It's better to replace
>Gateway with ASBRs.

Changed ³GW" in the diagram to ³ASBR².

>
>4.3 Among EVPN NVEs in Different DCs with GW
>
>   ... It also rewrites the
>   source MAC address with its own IRB Interface MAC address.
>
>Similar to 4.1, the above needs to be clear that it's the IRB interface
>for the subnet between the NVE and the GW. More below on this.

Done. Added "for the destination subnet (i.e., the subnet between NVE1 and
GW1)."

>
>   ... This implies that the GW1 needs to keep the remote
>   host MAC addresses along with the corresponding EVPN labels in the
>   adjacency entries of the IP-VRF table (i.e., its ARP table).	
>
>Does that mean GW1 needs to keep all type-2 IP/MAC addresses that GW2
>learns from NVEs in DC2?

Yes it does.

>Also does that mean GW1 and GW2 must be attached to all subnets?

That¹s correct.

> If so, between the source NVE and its local GW, when the source NVE
>route the traffic to the GW, I assume it's the destination subnet's IRB
>interface's mac address that will be used as the source mac address,

Correct. It is NVE1¹s destination subnet¹s IRB interface MAC address.

>and GW1's IRB mac address for the destination subnet is used as the dst
>mac address. It is true that an NVE may have the same system mac address
>for all its IRB interfaces, but it's good to point out which IRB is used
>(and if different IRB mac address is used, things will still work out).

I update the section 4.3. Please take a look at it (refer to the
attachment) and let me know if you have any further comments.

>
>Also, while each subnet is attached to each NVE, the IP routing process
>(e.g. TTL decrement) happens twice - first on the source NVE and then on
>the source GW. That's probably OK, but better point out all these details.

TTL decrement is given when IP lookup is performed at each hop.

>
>4.5 Use of Centralized Gateway
>
>   In this scenario, the NVEs within a given data center need to forward
>   traffic in L2 to a centralized L3GW for a number of reasons: a) they
>   don't have IRB capabilities or b) they don't have required policy for
>   switching traffic between different tenants or security zones.
>
>For b), do we configure IRB on those non-centralized gateways at all? I
>assume not (even though the NVE could support IRB) - It's better to be
>clear.

Yes, no IRB configuration. I added a sentence.

>
>I'll send a follow up email about the symmetric section.

OK. It sounds good.

Cheers,
Ali

>
>Thanks.
>
>Jeffrey
>
>> -----Original Message-----
>> From: BESS [mailto:bess-bounces@ietf.org] On Behalf Of Martin Vigoureux
>> Sent: Monday, February 13, 2017 5:07 PM
>> To: BESS <bess@ietf.org>
>> Subject: [bess] WG Last Call for
>>draft-ietf-bess-evpn-inter-subnet-forwarding-03
>> 
>> Hello Working Group,
>> 
>> This email starts a Working Group Last Call on
>> draft-ietf-bess-evpn-inter-subnet-forwarding-03 [1] which is considered
>> mature and ready for a final working group review.
>> Note that this call is longer than usual because we are pushing two
>> correlated documents together.
>> 
>> Please read this document if you haven't read the most recent
>> version yet, and send your comments to the list, no later than
>> *5th of March*.
>> Note that this is *not only* a call for comments on the document; it is
>> also a call for support (or not) to publish this document as a Proposed
>> Standard RFC.
>> 
>> *Coincidentally*, we are also polling for knowledge of any IPR that
>> applies to draft-ietf-bess-evpn-inter-subnet-forwarding, to ensure that
>> IPR has been disclosed in compliance with IETF IPR rules (see RFCs 3979,
>> 4879, 3669 and 5378 for more details).
>> 
>> *If* you are listed as a document author or contributor of
>> draft-ietf-bess-evpn-inter-subnet-forwarding-03 please respond to this
>> email and indicate whether or not you are aware of any relevant IPR.
>> 
>> Note that, as of today, no IPR has been disclosed against this document
>> or its earlier versions.
>> 
>> We are also polling for knowledge of implementations of part or all of
>> what this document specifies. This information is expected as per [2].
>> Please inform the mailing list, or the chairs, or only one of the
>>chairs.
>> 
>> Thank you,
>> M&T
>> 
>> [1]
>> 
>>https://datatracker.ietf.org/doc/draft-ietf-bess-evpn-inter-subnet-forwar
>>ding/
>> [2]
>> https://mailarchive.ietf.org/arch/msg/bess/cG3X1tTqb_vPC4rg56SEdkjqDpw
>> 
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