Hi,
I have a question about the rule for detection of duplicate MAC addresses in
Section 15.1 of
draft-ietf-bess-rfc7432bis<https://datatracker.ietf.org/doc/html/draft-ietf-bess-rfc7432bis-10#section-15.1>.
The problematic text is copied below (with the relevant fragments highlighted)
admits two interpretations:
a PE that detects a MAC mobility event via local learning starts an M-second
timer (with a default value of M = 180), and if it detects N MAC moves before
the timer expires (with a default value of N = 5), it concludes that a
duplicate-MAC situation has occurred
I.e.:
* The first MAC Move event that triggers the PE attempt to detect
duplication MUST be detected via local learning (and therefore results in
increment of the sequence number for the corresponding MAC address by the PE in
question)
* There is no explicit "via local learning" qualification for the
consequent MAC Move events that are counted to decide whether the MAC address
in question is duplicate or not.
IMHO this ambiguity may result in different decisions by the affected PEs.
Please consider the following scenario:
1. An EVPN BD is instantiated in PE-1, PE-2 and PE-3. In each of these PEs
it is attached to a single-homed Ethernet segment via a single AC
2. Initially MAC address X is locally learned by PE-1
3. Then X is locally learned by PE-2 that starts the M-seconds timer
4. After that X is locally learned by PE-3, PE-1, PE-3, PE- 1 and so on -
but not by PE-2 - while the M-seconds timer in PE-2 is still running. All these
events are identified by PE-2 as MAC Move events - but not via local learning:
* If PE-2 counts these MAC Move events for the purpose of duplicate MAC
detection, it declares X as duplicate and alerts the operator - even if it did
not participate in in
* Otherwise, PE-2 does not declare X as duplicate.
I understand that the example above is a corner case, but. IMHO and FWIW, it
should be resolved.
Can you please clarify, which of the above interpretations of the rule is
correct and, in any case, clarify this point in the next revision of the draft?
Regards, and lots of thanks in advance,
Sasha
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