Which of the following statements are true about IS-IS single topology? (Select two.)

Question

Options

• AA router running IS-IS for both IPv4 and IPv6 will not form an adjacency with a router running IS-
• BIPv6 is not supported by IS-IS single topology.
• CA router running IS-IS for both IPv4 and IPv6 will form an adjacency with a router running IS-IS
• DA router running IS-IS for both IPv4 and IPv6 will form an adjacency with a router running IS-IS

• A
  8% (2)
• B
  12% (3)
• C
  80% (20)

Explanation

In IS-IS single topology mode, IPv4 and IPv6 share a single SPF tree and a single set of adjacencies. The key characteristic is that adjacency formation is based on the IS-IS protocol itself (running at Layer 2), not on IP addressing. C is correct: A router running IS-IS for both IPv4 and IPv6 WILL form an adjacency with a router running IS-IS for IPv4 only in single topology - the adjacency is not blocked just because address families differ. D is correct and extends this: in single topology, even with mismatched address family configurations, adjacencies are established because IS-IS does not enforce address-family symmetry for adjacency formation (unlike multi-topology mode). A is false because single topology does NOT block adjacency formation due to IPv6 mismatches - that behavior would be associated with multi-topology IS-IS where separate topologies are maintained and stricter consistency is enforced. B is false because IS-IS single topology does support IPv6; it carries IPv6 reachability TLVs within the same topology as IPv4.

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