Brocade TurboIron 24X Series Configuration Guide - Manual (Page 494)

460 Brocade TurboIron 24X Series Configuration Guide
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Configuring IP parameters – Layer 3 Switches
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 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that are no longer valid.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 – 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.
ARP aging period is performed on route entry.
To globally change the ARP aging parameter to 20 minutes, enter the following command.
TurboIron(config)#ip arp-age 20
Syntax: ip arp-age
The parameter specifies the number of minutes and can be from 0 – 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.
TurboIron(config-if-e10000-1)#ip arp-age 30
Syntax: [no] ip arp-age
The parameter specifies the number of minutes and can be from 0 – 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.
For example, if Proxy ARP is enabled on a Layer 3 Switch connected to two subnets, 10.10.10.0/24
and 10.20.20.0/24, the Layer 3 Switch can respond to an ARP request from 10.10.10.69 for the
MAC address of the device with IP address 10.20.20.69. In standard ARP, a request from a device
in the 10.10.10.0/24 subnet cannot reach a device in the 10.20.20.0 subnet if the subnets are on
different network cables, and thus is not answered.
NOTE
An ARP request from one subnet can reach another subnet when both subnets are on the same
physical segment (Ethernet cable), since MAC-layer broadcasts reach all the devices on the
segment.