As shown in the figure, according to the analysis in the figure, which of the following routes cannot be introduced into OSPF 1? (Multiple choice) [R_Edge]ip ip-prefix aa index 10 deny 1.1.1.0 24…

Question

Options

• A1.1.1.1/32
• B1.1.1.0/24
• C1.1.1.2/32
• D1.1.1.2/16

• A
  29% (5)
• B
  71% (12)

Explanation

Routes B, C, and D are blocked because only 1.1.1.1/32 survives the prefix list filter.

The ip-prefix list "aa" works sequentially: index 10 explicitly denies 1.1.1.0/24 (exact match - network address and prefix length must both match), index 20 explicitly permits 1.1.1.1/32, and an implicit deny-all blocks everything else. The route-policy then passes only what the prefix list permits into OSPF 1 via redistribution.

• B (1.1.1.0/24) hits index 10's explicit deny - blocked before reaching the permit rule.
• C (1.1.1.2/32) misses both index 10 (wrong host) and index 20 (wrong host) - falls through to the implicit deny.
• D (1.1.1.2/16) similarly misses both named entries - also hits the implicit deny.
• A (1.1.1.1/32) is the only route that matches index 20's permit - it passes and can be redistributed into OSPF 1, making it the distractor that's not a correct answer.

Memory tip: Think of ip-prefix as an exact-match filter on both the network address and the mask length - a "close" address like 1.1.1.2 or a "close" length like /16 won't match /32, and anything not explicitly permitted falls into the invisible "deny all" at the bottom.

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