NOTE
If you want to change a previously congured the ARP rate limiting policy, you must remove the previously congured 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ensures that the ARP cache does not retain learned entries that are no longer valid.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 aects 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.
NOTE
Host devices connected to an ICX 7750 that also have a valid IP address and reply periodically to the arp request are not timed
out, even if no trac is destined for the device. This behavior is restricted to only ICX 7750 devices.
To globally change the ARP aging parameter to 20 minutes, enter the ip arp-age command.
device(config)# ip arp-age 20
Syntax: [no] ip arp-age num
The num parameter species the number of minutes, which can be from 0 through 240. The default is 10. If you specify 0, aging is
disabled.
To override the globally congured IP ARP age on an individual interface, enter the ip arp-age command followed by the new value at
the interface conguration level.
device(config-if-e1000-1/1/1)# ip arp-age 30
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.
Because 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
dierent 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), because MAC-layer broadcasts reach all the devices on the segment.
Proxy ARP is disabled by default on Brocade Layer 3 switches. This feature is not supported on Brocade Layer 2 switches.
You can enable proxy ARP at the Interface level, as well as at the Global CONFIG level, of the CLI.
NOTE
Conguring proxy ARP at the Interface level overrides the global
conguration.
Conguring IP parameters - Layer 3 switches
FastIron Ethernet Switch Layer 3 Routing
53-1003627-04 55
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