Refer to the exhibit. After configuring IS-IS on routers R1 and R2, an engineer notices that only the loopback interface at 2000:1::1 /96 is known to router R2. Which change must be made so that only

Question

Exhibit

Options

• AConfigure the router isis area1 command under the Loopback0 interface on R1.
• BRemove the advertise passive-only command under the IS-IS address family ipv6
• CRemove the ipv6 router isis area1 command under the Loopback2 interface on R1.
• DRemove the passive-interface Loopback0 command under the router isis area1 configuration.

• A
  4% (1)
• B
  7% (2)
• C
  67% (18)
• D
  22% (6)

Explanation

Removing ipv6 router isis area1 from Loopback2 is correct because that command makes Loopback2 an active IS-IS interface. With advertise passive-only configured in the IS-IS IPv6 address family, only passive IS-IS interfaces have their prefixes advertised - active IS-IS interfaces are excluded. The exhibit's redistribute connected configuration picks up Loopback2's prefix only when it is not an IS-IS interface, so removing ipv6 router isis area1 allows it to be redistributed (and thus advertised) while bypassing the passive-only filter entirely.

Why the distractors are wrong:

• A is wrong because Loopback0 already participates in IS-IS - adding the command again is redundant and doesn't stop Loopback0 from being advertised.
• B is wrong because removing advertise passive-only would cause all IS-IS-enabled interfaces to be advertised, meaning both Loopback0 and Loopback2 would appear - not just Loopback2.
• D is wrong because removing passive-interface Loopback0 makes Loopback0 an active IS-IS interface (stopping its advertisement under passive-only), but does nothing to get Loopback2 advertised.

Memory tip: Think of advertise passive-only as "IS-IS will only shout the address of interfaces that are listening, not talking." Assigning ipv6 router isis to an interface makes it talk (active), which silences it under passive-only - remove IS-IS from the interface to let redistribution carry its prefix instead.

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