Hi,
A have a question regarding usage of EVPN fast failover mechanisms in
combination with the port-active multi-homing mode as defined in the
corresponding
draft<https://datatracker.ietf.org/doc/html/draft-ietf-bess-evpn-mh-pa-04>.
Please configure the following scenario:
1. There are 3 PEs in the setup: PE-1, PE-2 and PE-3, and an EVI that is
present in all of them.
2. The EVI in PE-1 and PE-2 is attached to a Port-Active MH ES (i.e.
configuration is consistent) that uses Highest Preference-based Df election
method
* PE-1 is elected as the DF and activates the corresponding local port
* PE-2 is elected as the Backup DF (BDF) in accordance with and blocks
the corresponding port for customer traffic
* Both PE-1 and PE-2 advertise per-EVI EVPN Type 1 route for the EVI in
question (please note that this requires PE-2 to differentiate between failed
ports and ports that it has decided to deactivate)
3. PE-1 learns multiple IP→MAC pairs from the MH ES in question and
advertises it as an EVPN Type 2 route. As a consequence, PE-3 creates a pair of
FDB entries for the MAC addresses in these pairs:
* The active FDB entry in each pair entry points to PE-1 (because it has
advertised an EVPN Type 2 route for the IP→MAC pair) and uses the label
received in the Label1 field of the corresponding EVPN Type 2 route
* The backup FDB entry in each points to PE-2 (because it has only
advertised a per EVI EVPN Type 1 route for the EVI in question) and uses the
label received in the Label field of the per-EVI EVPN Type 1 route
4. When the PE-CE link that is part of the MH ES in question fails in PE-1,
it immediately withdraws the per ES EVPN Type 1 route for this MH ES
* As a consequence, PE-3 activates the backup FDB entries for all MAC
addresses it has learned from PE-1 and starts sending traffic to PE-2
* However, withdrawal of the per-ES EVPN-Type 1 route by and of itself
will not trigger re-election of the DF. As a consequence, the port in PE-2
shall remain blocked until:
i. The EVPN
Type 4 route advertised by PE-1 for the MH ES in question is withdrawn
ii. The DF
Election timer (started when the EVPN Type 4 route is withdrawn, by default 3
seconds) expires.
>From my POV the above means that known unicast traffic sent by PE-3 toward the
>CEs on the MH ES shall be lost at least for the duration of the DF Election
>timer (could be more if withdrawal of the EVPN Type 4 route by PE-1 is not
>prioritized). Do I miss something substantial here?
IMHO and FWIW the situation could be improved if the BDF on the Port-Active MH
ES, upon detection of the per-ES EVPN Type 1 route for the MH ES in question by
the PE that has been elected as the DF, would immediately assume the DF role
and activates the corresponding port. But the Port-Active Multi-Homing draft
does not define such behavior.
Your timely feedback would be highly appreciated.
Regards, and lots of thanks in advance,
Sasha
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Email: alexander.vainsht...@rbbn.com
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