Dell BigIron RX Series, Configuration Manual

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190 BigIron RX Series Configuration Guide
53-1002253-01
Configuring ARP parameters
7
Clearing the rate limit for ARP packets
To clear the ARP port rate limit data on every port of the LP, enter a command such as the
following.
LP-1# clear ip traffic arp
Changing the ARP aging period
When the device places an entry in the ARP cache, the device 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 The aging timer ensures that the ARP cache does not retain learned entries that are no
longer valid.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 the device, you can change the ARP age to a value from 0 – 240 minutes. 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 following command.
BigIron RX(config)# ip arp-age 20
Syntax: ip arp-age <num>
The <num> 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.
BigIron RX(config-if-e1000-1/1)# ip arp-age 30
Enabling proxy ARP
Proxy ARP allows the device 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 the device connected to two subnets, 10.10.10.0/24 and
20.20.20.0/24, the device can respond to an ARP request from 10.10.10.69 for the MAC address
of the device with IP address 20.20.20.69. In standard ARP, a request from a device in the
10.10.10.0/24 subnet cannot reach a device in the 20.20.20.0 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.
Proxy ARP is disabled by default.
To enable IP proxy ARP, enter the following command.
BigIron RX(config)# ip proxy-arp
To again disable IP proxy ARP, enter the following command.
BigIron RX(config)# no ip proxy-arp