Refer to the exhibit. A network operator must stop 10.33.33.33/32 from being redistributed into Level 1 router XR1. Which configuration meets this need? A. B. C. D.

Question

Exhibits

Options

• A#XR2 prefix-set NO_33 10.33.33.33/32 end-set ! route-policy ISIS_NO_33 if destination in NO_33 then drop else pass endif end-policy ! router isis 1 address-family ipv4 unicast propagate level 2 into level 1 route-policy ISIS_NO_33
• B#XR3 prefix-set NO_33 10.33.33.33/32 end-set ! route-policy ISIS_NO_33 if destination in NO_33 then drop endif end-policy ! router isis 1 address-family ipv4 unicast propagate level 2 into level 1 route-policy ISIS_NO_33
• C#XR3 prefix-set NO_33 10.33.33.33/32 end-set ! route-policy ISIS_NO_33 if destination in NO_33 then drop else pass endif end-policy ! router isis 1 address-family ipv4 unicast propagate level 2 into level 1 route-policy ISIS_NO_33

• A
  13% (2)
• B
  6% (1)
• C
  81% (13)

Explanation

In Cisco IOS XR, the propagate level 2 into level 1 command controls route leaking from IS-IS Level 2 into Level 1. This command must be configured on the L1/L2 boundary router that is propagating routes into the L1 area - that is XR3, not XR2. This rules out choice A immediately. Between B and C, the critical difference is the else pass clause. In IOS XR Routing Policy Language (RPL), if no else branch is defined, the implicit default action is to DROP all non-matched prefixes. Choice B would therefore drop 10.33.33.33/32 as intended, but it would also silently drop ALL other L2-learned prefixes, breaking reachability throughout Level 1. Choice C correctly drops only 10.33.33.33/32 and explicitly passes all other prefixes with else pass, which is the correct and complete solution.

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