Refer to the exhibit. An administrator is verifying that a CEF FIB entry exists to destination network 192.168.150.0. Given the output generated by the show ip cef and show adjacency detail commands, which three statements are true? (Choose three.)
A.
There is a valid CEF entry for the destination network 192.168.150.0.
B.
The “valid cached adjacency” entry indicates that CEF will put all packets going to such an adjacency to the next best switching mode.
C.
The counters (0 packets, 0 bytes) indicate a problem with the 192.168.199.3 next hop IP address.
D.
There is an adjacency for the 192.168.199.3 next hop IP address.
E.
The number 003071506800 is the MAC address of the 192.168.199.3 next hop IP address.
F.
The number 003071506800 is the MAC address of the source IP address.
Explanation:
The adjacency table contents are fundamentally a function of the ARP process, whereby Layer 2 addresses are mapped to corresponding Layer 3 addresses. When the router issues an ARP request, a corresponding reply is received, and a host entry is added to the adjacency table to reflect this. In addition, the router can also glean next hop routers from routing updates and make entries in the adjacency table to reflect this. This lets the router build the next hop rewrite information necessary for Layer 3 packet forwarding. By having this data already stored in a table, CEF can perform highly efficient and consistent forwarding, because no discovery process is required. The command show ip cef is used to view the contents of the CEF adjacency table from the MSFC2. The command show ip cef summary gives a brief overview of the CEF process. It shows information such as the total number of adjacencies and routes.
Each time an adjacency entry is created, a Layer 2 data link layer header for that adjacent node is precomputed and stored in the adjacency table. This information is subsequently used for encapsulation during CEF switching of packets. Output from the command show adjacency detail displays the content of the information to be used during this Layer 2 encapsulation. Verify that the header information is displayed as would be expected during Layer 2 operations, not using precomputed encapsulation from the adjacency table. Adjacency statistics are updated approximately every 60 seconds. Also, the show cef drops command will display an indication of packets that are being dropped due to adjacencies that are either incomplete or nonexistent. There are two known reasons for incomplete or nonexistent adjacencies. 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, and then it fails to clear the entry. The symptoms of an incomplete adjacency include random packet drops during a ping test. Use the debug ip cef command to view CEF drops caused by an incomplete adjacency.