Arp Purge - Dell PowerConnect 6224 Command Line Interface Manual

Command Mode
Global Configuration mode
User Guidelines
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.
Example
console#configure
console(config)#arp dynamicrenew
console(config)#no arp dynamicrenew

arp purge

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.
649
ARP Commands