FastIron Ethernet Switch Layer 3 Routing Configuration Guide

Part Number: 53-1002968-02

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), because MAC-layer broadcasts reach all the devices on the segment.

Proxy ARP is disabled by default on BrocadeLayer 3 switches. This feature is not supported on BrocadeLayer 2 switches.

You can enable proxy ARP at the Interface level, as well as at the Global CONFIG level, of the CLI.

NOTE: Configuring proxy ARP at the Interface level overrides the global configuration.

Enabling proxy ARP globally

To enable IP proxy ARP on a global basis, enter the ip proxy-arp command.

device(config)# ip proxy-arp

To again disable IP proxy ARP on a global basis, enter the no ip proxy-arp command.

device(config)# no ip proxy-arp

Syntax: [no] ip proxy-arp

Enabling IP ARP on an interface

NOTE: Configuring proxy ARP at the Interface level overrides the global configuration.

To enable IP proxy ARP on an interface, enter the following commands.

device(config)# interface ethernet 5
device(config-if-e1000-5)# ip proxy-arp enable

To again disable IP proxy ARP on an interface, enter the following command.

device(config)# interface ethernet 5
device(config-if-e1000-5)# ip proxy-arp disable

Syntax: [no] ip proxy-arp { enable | disable }

NOTE: By default, gratuitous ARP is disabled for local proxy ARP.