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[bess] Question on symmetric IRB procedures in draft-ietf-bess-evpn-inter-subnet-forwarding

Muthu Arul Mozhi Perumal <muthu.arul@gmail.com> Wed, 20 March 2019 04:49 UTC

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From: Muthu Arul Mozhi Perumal <muthu.arul@gmail.com>
Date: Wed, 20 Mar 2019 10:19:14 +0530
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Subject: [bess] Question on symmetric IRB procedures in draft-ietf-bess-evpn-inter-subnet-forwarding
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draft-ietf-bess-evpn-inter-subnet-forwarding says the following in section
3.2.2:

<snip>
   If the receiving PE receives this route with both the MAC-VRF and IP-
   VRF route targets but the MAC/IP Advertisement route does not include
   MPLS label2 field and if the receiving PE supports asymmetric IRB
   mode, then the receiving PE installs the MAC address in the
   corresponding MAC-VRF and <IP, MAC> association in the ARP table for
   that tenant (identified by the corresponding IP-VRF route target).
</snip>

Further below it says:

<snip>
   If the receiving PE receives this route with both the MAC-VRF and IP-
   VRF route targets but the MAC/IP Advertisement route does not include
   MPLS label2 field and if the receiving PE does not support either
   asymmetric or symmetric IRB modes, then if it has the corresponding
   MAC-VRF, it only imports the MAC address
</snip>

How should "does not support either asymmetric or symmetric IRB" be
interpreted? Should it be interpreted as "supports neither asymmetric nor
symmetric"? Or should it be interpreted as "does not support one of them"?

If it is the former, then the case where the receiving PE supports only
symmetric (but not asymmetric) IRB isn't described. It it is the later then
it includes the case where the receiving PE supports only asymmetric (but
not symmetric) IRB and what is described in that paragraph conflicts with
the first paragraph mentioned above.

Regards,
Muthu

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