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Debugging cached CEF adjacencies

A while ago I wrote about cached CEF adjacencies and the impact they have on ARP caching. If you ever need to, you can debug them with the debug ip cef table command. As this command might produce a lot of output in a production network, always use it in combination with an access-list that limits the debugging to the selected address range.

Alternatively, you can use the debug arp adjacency command, but you cannot limit its output with an access-list

For example, to test cached CEF adjacencies in subnet 10.0.0.0/24, I've used the following commands:
rtr#show ip access-list 99
Standard IP access list 99
10 permit 10.0.0.0, wildcard bits 0.0.0.255 (26 matches)
rtr#debug ip cef table 99
IP CEF table debugging is on for access list 99
rtr#debug arp
ARP packet debugging is on
rtr#ping 10.0.0.10

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.0.10, timeout is 2 seconds:

08:57:27: IP ARP: creating incomplete entry for IP address: 10.0.0.10 interface FastE
thernet0/0
08:57:27: IP ARP: sent req src 10.0.0.6 0016.c876.8b38,
dst 10.0.0.10 0000.0000.0000 FastEthernet0/0
08:57:27: IP ARP: rcvd rep src 10.0.0.10 000c.29a7.8ade, dst 10.0.0.6 FastEthernet0/0
08:57:27: CEF-IP: Checking dependencies of 10.0.0.0 255.255.255.0
08:57:27: CEF-Table: Adjacency-prefix 10.0.0.10 255.255.255.255 add request -- succee
ded.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 1/1/4 ms
rtr#

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