What is recommended for the routing protocol setup on leaf VSX pairs?

Question

Options

• AConfigure the leaf VSX members to establish neighbor relationships with each other over one of
• BHave the VSX members connect to each spine switch on an L3 VSX LAG and become neighbors
• CAdd a dedicated VLAN to the VSX ISL, assign it a /31 subnet, and run the routing protocol on it
• DDo not configure the routing protocol to run directly between the leaf VSX members

• A
  10% (3)
• B
  14% (4)
• C
  72% (21)
• D
  3% (1)

Explanation

Option C is correct because the VSX ISL (Inter-Switch Link) is the most reliable and appropriate path for establishing a routing protocol adjacency between leaf VSX members - dedicating a VLAN on the ISL with a /31 subnet keeps routing traffic isolated and ensures the pair maintains synchronized routing state without depending on production uplinks.

Why the distractors are wrong:

• Option A is wrong because establishing neighbor relationships over a standard uplink introduces dependency on a production path that may carry data traffic, creating instability if that link flaps.
• Option B is wrong because L3 VSX LAGs toward spines are for upstream connectivity, not for building adjacency between the VSX leaf members themselves - routing over those LAGs doesn't solve the intra-pair synchronization problem.
• Option D is wrong because skipping the routing protocol between VSX members leaves the pair unable to share and synchronize routing information, defeating the purpose of the VSX design.

Memory tip: Think of the ISL as a "private backbone" - just as you'd give a dedicated /31 to any point-to-point routing link, do the same on a dedicated VLAN over the ISL so the VSX pair can talk routing without touching production traffic. ISL = Isolated routing Subnet Link.

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