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Exam 300-101 Question id=393 Network Principles

Refer to the exhibit.
Router#show adjacency Protocol Interface Address ------------------------------------------------------------ IP Serial0 192.168.209.130(2) (incomplete) IP Serial0 192.168.209.131(7) IP Ethernet0 192.168.201.1(7)
A network administrator checks this adjacency table on a router. What is a possible cause for the incomplete marking?

A. incomplete ARP information
B. incorrect ACL
C. dynamic routing protocol failure
D. serial link congestion
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To display information about the Cisco Express Forwarding adjacency table or the hardware Layer 3-switching adjacency table, use the show adjacency command.
Reasons for Incomplete Adjacencies
There are two known reasons for an incomplete adjacency:

  • The router cannot use ARP successfully for the next-hop interface.
  • After a clear ip arp or a clear adjacency command, the router marks the adjacency as incomplete. Then it fails to clear the entry.
In an MPLS environment, IP CEF should be enameled for Label Switching. Interface level command ip route-cache cef
No ARP Entry
When CEF cannot locate a valid adjacency for a destination prefix, it punts the packets to the CPU for ARP resolution and, in turn, for completion of the adjacency.

Reference