Hi all,
I noticed that the DF-election for VLAN-based/VLAN-bundle service interface has
been modified in section 8.5 of rfc7432bis.
"3. When the timer expires, each PE ... ... The ordinals are used to determine
which PE node will be the DF for a given EVPN instance on the Ethernet segment,
using the following rule: Assuming a redundancy group of N PE nodes, the PE
with ordinal i is the DF for an <ES, EVI> when (V mod N) = i, where V is the
Ethernet tag for that EVI. For VLAN-Aware Bundle service, then the numerically
lowest Ethernet tag in that EVI MUST be used in the modulo function."
If the EVIs are all VLAN-based or VLAN-bundle and above Ethernet tag is the
Ethernet Tag ID of the corresponding A-D per EVI route, the Ethernet tag for
each EVI will be 0. Thus above i will be 0 for each of these EVIs. But the goal
of service carving is "The load-balancing procedure carves the set of EVIs on
that ES among the PEs nodes evenly such that every PE is the DF for a disjoint
and distinct set of EVIs for that ES."
How can this goal be achieved for VLAN-based or VLAN-bundle service? As far as
I know, RFC7432 didn't say that V is the ethernet tag ID for that EVI.
I understand that in AC-DF mode (AC-influenced DF-election) , the Ethernet tag
for that EVI should be used to match a corresponding A-D per EVI route.
But if the modulo function is done using Ethernet Tag ID, the load-balancing
cannot be evenly done for VLAN-based and VLAN-bundle service interface.
I guess, according to original RFC7432, when the modulo function is done, the V
should be the original VLAN on that AC, especially in VLAN-based service
interface and VLAN-aware bundle service interface with VID translation
(https://datatracker.ietf.org/doc/html/draft-ietf-bess-rfc7432bis-07#name-vlan-aware-bundle-service-i),
where the VID is not the same as the ethernet Tag ID.
Is my understanding correct? Have I missed something important?
Furthermore, the lowest Ethernet Tag ID for all VLAN-aware bundle EVIs may be
the same value, I guess it may be 0 or 1. In such case, the load-balancing
cannot be evenly done for VLAN-aware bundle service interface either.
So maybe it should be said as the following: For VLAN-Aware Bundle service,
then the numerically lowest Ethernet tag on that <ES, EVI> MUST be used in
AC-DF mode, and the VID corresponding to that lowest ethernet Tag ID of that
<ES, EVI> is used in the modulo function.
The last question is that: If an ES are attached to serveral VLAN-aware bundle
EVIs, can these EVIs use the same Ethernet Tag ID for that ES?
If they can, then using ethernet tag ID to do the modulo function may not be a
good choice.
Thanks,
Yubao
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