The following is part of the output configuration of the Huawei router. [Huawei]ip-prefix IP prefix 5 deny 10.0.0.0 [Huawei]ip-prefix IP prefix 10 permit 192.0.0.0 greater-equal 16 less-equal 32…

Question

Options

• AWhen the router advertises its BGP route to BGP neighbor 12.12.12.2, it will allow the advertisement of routes 10.0.0.0~10.255.255.255
• BWhen the router advertises its BGP routes to BGP neighbor 12.12.12.2, it will filter out all routes
• CWhen the router advertises its BGP route to BGP neighbor 12.12.12.2, it will only allow routes 172.16.0.0~172.31.255.255
• DWhen the router advertises its BGP route to BGP neighbor 12.12.12.2, it will allow the advertisement of routes 172.0.0.0~172.31.255.255

• A
  6% (3)
• B
  14% (7)
• C
  76% (37)
• D
  4% (2)

Explanation

The prefix-list is applied as an export filter to BGP neighbor 12.12.12.2, processing entries in ascending index order with an implicit deny-all at the end; only index 20 effectively permits routes, specifically subnets of 172.16.0.0/12 (prefix lengths up to /32), which spans exactly 172.16.0.0 through 172.31.255.255, making C correct. Option A is wrong because index 5 explicitly denies 10.0.0.0 routes before they can reach any permit entry. Option B is wrong because 172.16.0.0/12 routes do pass the filter, so not all routes are blocked. Option D is wrong because the /12 mask anchors the permitted block at 172.16.0.0, not 172.0.0.0 - addresses from 172.0.0.0 to 172.15.255.255 fall outside that /12 boundary and are caught by the implicit deny-all.

Memory tip: A Huawei ip-prefix list always ends with an implicit deny-all. To evaluate any route, trace it through the numbered entries in strict ascending index order and stop at the first match - if no entry matches, the route is denied. Practice stepping through small prefix-lists entry by entry rather than reading them as a block.

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