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#

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 192.168.1.3/24
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 192.168.1.2 8 0001. 9670. b780 ARPA Ethernet0
Internet 192.168.1.3 - 0000. 0c92. bc6a ARPA Ethernet0
Internet 192.168.1.4 9 0010. 4b09. 5700 ARPA Ethernet0
Internet 192.168.1.5 2 0010. 4b09. 5715 ARPA Ethernet0
Router#

Age gets reset to 0 when router sees traffic from device

Clear entire ARP cache

Router#clear arp
Router#

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