Configuration Guide User guide

FastIron Configuration Guide 983
53-1002494-02
Configuring IP parameters – Layer 3 Switches
To limit the number of ARP packets the device will accept each second, enter the rate-limit-arp
command at the global CONFIG level of the CLI.
Brocade(config)# rate-limit-arp 100
This command configures the device to accept up to 100 ARP packets each second. If the device
receives more than 100 ARP packets during a one-second interval, the device drops the additional
ARP packets during the remainder of that one-second interval.
Syntax: [no] rate-limit-arp <num>
The <num> parameter specifies the number of ARP packets and can be from 0 through 100. If you
specify 0, the device will not accept any ARP packets.
NOTE
If you want to change a previously configured the ARP rate limiting policy, you must remove the
previously configured policy using the no rate-limit-arp <num> command before entering the new
policy.
Changing the ARP aging period
When the Layer 3 Switch places an entry in the ARP cache, the Layer 3 Switch also starts an aging
timer for the entry. The aging timer ensures that the ARP cache does not retain learned entries that
are no longer valid. An entry can become invalid when the device with the MAC address of the entry
is no longer on the network.
The ARP age affects dynamic (learned) entries only, not static entries. The default ARP age is ten
minutes. On Layer 3 Switches, you can change the ARP age to a value from 0 through 240 minutes.
You cannot change the ARP age on Layer 2 Switches. If you set the ARP age to zero, aging is
disabled and entries do not age out.
To globally change the ARP aging parameter to 20 minutes, enter the ip arp-age command.
Brocade(config)# ip arp-age 20
Syntax: ip arp-age <num>
The <num> parameter specifies the number of minutes and can be from 0 through 240. The
default is 10. If you specify 0, aging is disabled.
To override the globally configured IP ARP age on an individual interface, enter a command such as
the following at the interface configuration level.
Brocade(config-if-e1000-1/1)# ip arp-age 30
Syntax: [no] ip arp-age <num>
The <num> parameter specifies the number of minutes and can be from 0 through 240. The
default is the globally configured value, which is 10 minutes by default. If you specify 0, aging is
disabled.
Enabling proxy ARP
Proxy ARP allows a Layer 3 Switch to answer ARP requests from devices on one network on behalf
of devices in another network. Since ARP requests are MAC-layer broadcasts, they reach only the
devices that are directly connected to the sender of the ARP request. Thus, ARP requests do not
cross routers.