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arp dynamicrenew
Use the arp dynamicrenew command in Global Configuration mode to
enable the ARP component to automatically renew dynamic ARP entries
when they age out. To disable the automatic renewal of dynamic ARP entries
when they age out, use the no form of the command.
Syntax
arp dynamicrenew
no arp dynamicrenew
Default Configuration
The default state is enabled.
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, 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, and 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. If the ARP cache is full and a new host is
learned, the oldest ARP cache entry is replaced with the new host entry.In a
network where the number of potential neighbors is greater than the ARP
1192
Layer 3 Routing Commands
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