Tuesday, November 23, 2010

Manage Cisco Router's ARP Cache

Default ARP timeout is 4 hours

Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config) #interface Ethernet0
Router(config-if) #arp timeout 600 (600 seconds)
Router(config-if) #end

Router#show interface Ethernet0
Ethernet0 is up, line protocol is up
Hardware is Lance, address is 0000. 0c92. bc6a (bia 0000. 0c92. bc6a)
Internet address is
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255
Encapsulation ARPA, loopback not set, keepalive set (10 sec)
ARP type: ARPA, ARP Timeout 00:10:00

Router#show ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 8 0001. 9670. b780 ARPA Ethernet0
Internet - 0000. 0c92. bc6a ARPA Ethernet0
Internet 9 0010. 4b09. 5700 ARPA Ethernet0
Internet 2 0010. 4b09. 5715 ARPA Ethernet0

Age gets reset to 0 when router sees traffic from device

Clear entire ARP cache

Router#clear arp

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