DELL PC6224F User Manual

ARP Commands

Global Configuration mode

When an ARP entry reaches its maximum age, the system must decide 

whether to retain or delete the entry. If the entry has recently been used to 

forward data packets, the system will renew the entry by sending an ARP 

request to the neighbor. If the neighbor responds, the age of the ARP cache 

entry is reset to 0 without removing the entry from the hardware. Traffic to 

the host continues to be forwarded in hardware without interruption.  If the 

entry is not being used to forward data packets, then the entry is deleted from 

the ARP cache, unless the dynamic renew option is enabled. If the dynamic 

renew option is enabled, the system sends an ARP request to renew the entry. 

When an entry is not renewed, it is removed from the hardware and 

subsequent data packets to the host trigger an ARP request. Traffic to the 

host is lost until the router receives an ARP reply from the host. Gateway 

entries, entries for a neighbor router, are always renewed. The dynamic renew 

option only applies to host entries.
The disadvantage of enabling dynamic renew is that once an ARP cache entry 

is created, that cache entry continues to take space in the ARP cache as long 

as the neighbor continues to respond to ARP requests, even if no traffic is 

being forwarded to the neighbor. In a network where the number of potential 

neighbors is greater than the ARP cache capacity, enabling dynamic renew 

could prevent some neighbors from communicating because the ARP cache is 

full.

console#configure

console(config)#arp dynamicrenew

console(config)#no arp dynamicrenew

Use the arp purge command in Privileged EXEC mode to cause the specified 

IP address to be removed from the ARP cache. Only entries of type dynamic 

or gateway are affected by this command.