Examine the following output.
What possible reason(s) can cause the state of the first entry in the adjacency table? (Choose all that apply.)
A. the interface is a multipoint interface
B. the clear ip arp command was executed
C. the Layer 3 information is unknown
D. the clear adjacency command was executed
Explanation:
If either the clear ip arp or the clear adjacency commands were issued, the entry would temporarily be listed as incomplete in the adjacency table. The adjacency table is used by Cisco Express Forwarding (CEF) to maintain Layer 2 information about the next hop to remote networks. In CEF, an adjacency refers to a control structure that holds Layer 2 information for an IP address on a particular interface. When that information is not available the entry will be listed as incomplete, as shown in the example.
Layer 2 information normally comes from the ARP process. Therefore, if the ARP table is cleared with the clear ip arp command, the Layer 2 information will be temporarily unavailable until the ARP process re-learns it the next time a frame must be sent to that hop. Moreover, if the adjacency table is emptied with the clear adjacency command, the entry must be created again. This will also result in the entry being marked incomplete for a short period of time until the ARP table can be consulted and the Layer 2 information re-added.
The interface in the scenario is not a multipoint interface. A multipoint interface would include entries for multiple next hops, since a multipoint interface connects to multiple Layer 3 destinations. An example of this is shown below in sample output from a Frame Relay interface:
The layer 3 information of the next hop is present in the entry in the scenario example. It is 10.10.10.2.
Objective:
Network Principles
Sub-Objective:
Identify Cisco Express Forwarding concepts