Discuss Nokia 4A0-D03 Exam Topic 5 Question 3

Which of the following statements about MAC mobility is TRUE?

AThe original PE advertises the locally learned MAC with the sequence number set to a maximum value.

BA PE advertising a local MAC that was previously learned through EVPN, will decrement the sequence number in its update.

CThe originating PE generates a withdraw message after the same locally learned MAC has aged out.

DThe originating PE and the destination PE must synchronize their MAC tables.

Suggested Answer: C

Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

MAC mobility is the EVPN mechanism used when a host MAC moves from one PE to another. The control plane uses a MAC Mobility extended community and sequence number behavior to determine the most recent valid location for the MAC. When a PE locally learns a MAC that was previously learned through EVPN, it advertises the MAC with an incremented sequence number, allowing remote PEs to prefer the newer location. Therefore, option B is wrong because the sequence number is not decremented. Option A is also wrong because the original PE does not advertise the locally learned MAC with a maximum sequence value as a normal mobility procedure. Option D is inaccurate because PEs do not need direct MAC table synchronization; they rely on EVPN control-plane advertisements and withdrawals. The true statement is option C: the originating PE generates a withdraw message after the same locally learned MAC ages out. This withdrawal removes stale reachability from remote PEs and prevents continued forwarding toward a PE that no longer has the host locally attached. Reference: EVPN MAC mobility, sequence-number handling, MAC route withdrawal after aging.

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12 comments · newest first

Mabelle 1 month ago

I feel C is misleading. Withdraw messages are not always generated after aging out.

Britt 2 months ago

I disagree, B makes more sense. Decrementing the sequence number shows updates properly.

Dolores 2 months ago

I think option A is correct. The sequence number should be maxed out for stability.

Emile 2 months ago

Wait, are we really saying the PE can just forget MACs? That seems odd!

Glenna 2 months ago

D seems a bit off, I don't think they need to sync MAC tables.

Carmela 2 months ago

C sounds right, aging out usually triggers a withdraw.

Nu 2 months ago

I think B is correct, I've seen that behavior in EVPN setups.

Shay 3 months ago

A is definitely false, sequence numbers don't max out like that.

Diane 3 months ago

Option D seems plausible, but I’m not sure if synchronization is necessary for MAC mobility. I need to double-check my notes on that.

Mozell 3 months ago

I’m a bit confused about option C. I thought a withdraw message was only generated under specific conditions, but I can’t recall the details.

Laurena 3 months ago

I feel like I’ve seen a question similar to this before, and I’m leaning towards option B. It makes sense that the sequence number would decrement when updating.

Chuck 3 months ago

I think option A sounds familiar, but I’m not entirely sure if it’s correct. I remember something about sequence numbers being involved.

Nokia 4A0-D03 Exam - Topic 5 Question 3 Discussion