300-410 Question #69: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. In which circumstance does the BGP neighbor remain in the idle condition? R200#show ip bgp summary BGP router identifier 10.1.1.1, local AS number 65000 BGP table version is 26, main routing table version 26 1 network entries uses 132 bytes of memory 1 path entries uses 92 bytes of memory 2 BGP path/bestpath attribute entries using 296 bytes of memory 0 BGP route-map cache entries using 0 bytes of memory 0 BGP filter-list cache entries using 0 bytes of memory Bifidist cache mines: current 1 (at peak 2) using 28 bytes of memory BGP using 248 total bytes of memory BGP activity 24/23 prefixes, 24/23 paths, scan interval 60 secs Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 192.0.2.2 4 65100 20335 20329 0 0 0 00:02:04 Idle (PfxCt) R200#

Options

• AIf prefixes are not received from the BGP peer
• BIf prefixes reach the maximum limit
• CIf a prefix list is applied on the inbound direction
• DIf prefixes exceed the maximum limit

Explanation

The BGP neighbor remains in the Idle state with a 'PfxCt' (Prefix Count) indication when the number of received prefixes from that neighbor exceeds the configured maximum limit.

Common mistakes.

• A. If prefixes are not received, the neighbor might be in a 'Connect' or 'Active' state if it's attempting to establish, or 'Established' with zero prefixes if the session is up but no routes are exchanged.
• B. If prefixes merely 'reach' the maximum limit, a warning might be issued, but the session typically enters Idle only if the limit is 'exceeded' and a reset action is configured.
• C. Applying an inbound prefix list filters which prefixes are accepted into the routing table, but it does not cause the BGP session itself to enter the Idle (PfxCt) state; the session would likely remain 'Established' with fewer prefixes received.

Concept tested. BGP neighbor states, maximum-prefix limit

Reference. https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/211516-bgp-states-explanation.html

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