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Chapter 4 Configuring the Address Resolution Protocol
Immediately Refreshing the Bridge Forwarding Table for a MAC Down Event
4-4
Cisco Content Services Switch Routing and Bridging Configuration Guide
OL-8241-02
Immediately Refreshing the Bridge Forwarding
Table for a MAC Down Event
By default, when the CSS receives a Down event for a MAC address in the bridge
forwarding table, it may not send an ARP request to an IP address associated with
that MAC address for up to 60 seconds to refresh the table. During this time, the
bridge flows through the CSS to the MAC address could fail.
You can configure the CSS to immediately send an ARP request for an IP address
associated with that MAC address, thus immediately repopulating the entries in
bridge forwarding table. Use the global configuration mode arp
mac-down-immediate command.
For example, enter:
(config)# arp mac-down-immediate
Note Under certain network conditions, such as STP convergences, the CSS may
appear to be causing an ARP storm.
To reset the default behavior, enter:
(config)# no arp mac-down-immediate
Configuring ARP Timeout
To set the time, in seconds, to hold an ARP resolution result, use the arp timeout
command. When you change the timeout value, this value affects only new ARP
entries. All previous ARP entries retain the old timeout value. This timeout value
affects only dynamic ARP entries. Static ARP entries are permanent and are not
affected by this timeout.
The timeout value is the number of seconds the CSS holds an ARP resolution
result. To set a timeout value, enter an integer from 60 to 86400 (24 hours)
seconds. The default is 14400 seconds (4 hours). If you do not want the ARP
entries to time out, enter none or 86401.
For example:
(config)# arp timeout 120