Install guide
30 Deleting Dynamic ARP Entries Release Note
Software Version 2.7.6
C613-10462-00 REV A
Deleting Dynamic ARP Entries
Address Resolution Protocol (ARP) is used by the router or switch to
dynamically learn the location of devices in its networks. When the router or
switch receives a packet with an unknown destination address, it broadcasts an
ARP request to determine where to send that packet. When a host replies and
identifies itself as the destination for that address, the router or switch records
this information in a dynamic ARP entry in its ARP cache. It uses that ARP
entry to forward further packets to that address. Such dynamic ARP entries age
out if there is no traffic to that address for (by default) 17-34 minutes. This
removes entries for disconnected devices and devices that change their IP
addresses.
If you swap a device in your network for another device that has the same IP
address, the router or switch may be left with a stale ARP entry and be unable
to forward packets to the new device. This is most likely if you swap in the
device without taking the link to the router or switch down, for example, if it
connects through a hub. Instead of waiting for such entries to time out, you can
delete them.
Previous software versions allow you to delete individual ARP entries.
Software Version 2.7.6 also lets you delete all dynamic entries in a single step.
This is particularly useful if you do not know the relevant IP addresses.
The router or switch replaces the deleted ARP entries when it receives traffic
for the relevant addresses. As long as the entries are relearnt quickly enough,
deleting dynamic ARP entries does not affect:
■ routes
■ OSPF neighbour status
■ BGP peer status
■ the TCP/UDP connection status
■ VRRP status
To delete a single dynamic or static entry, use the command:
delete ip arp=ipadd
To delete all dynamic ARP entries, use the new alldynamic option in the
command:
delete ip arp=alldynamic
The alldynamic option does not delete static (manually-entered) ARP entries.
The router or switch generates a log message to record that dynamic ARP
entries have been deleted.
Command Change Summary
The following table summarises the modified commands (see Command
Reference Updates).
Command Change
delete ip arp New alldynamic option