Enabling local proxy arp – Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) User Manual
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Multi-Service IronWare Switching Configuration Guide
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Configuring ARP parameters
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Enabling local proxy ARP
Under some Layer-2 configurations such as uplink-switch or private VLAN, broadcast packets are
not flooded to every port in a VLAN. In these configurations, an ARP request from one host may not
reach another host. Enabling the Local Proxy ARP feature on a port directs the device to reply on
behalf of a target host if it exists. The ARP reply returned contains the device’s mac address
instead of the mac address of the target host. In this transaction, the traffic sent to the target host
is Layer-3 forwarded rather than Layer-2 switched.
To enable Local Proxy ARP, the global-level command ip proxy-arp must first be enabled as
described in
on page 751. After ip proxy-arp has been enabled globally, Local
Proxy ARP can be enabled on a specified interface using the following command.
Brocade(config-if-e1000-1/1)# interface ethernet 1/1
Brocade(config-if-e1000-1/1)# ip local-proxy-arp
Syntax: [no] ip local-proxy-arp
Disabling gratuitous ARP requests for local proxy ARP
When the Local Proxy ARP is configured under the IP interface, the Brocade device will reply to ARP
requests on behalf of the hosts inside the subnet using its own MAC address. Refer to
on page 752 for information on configuring the Local Proxy ARP command. In this
configuration, when a host comes up, the host tries to ping its own IP address to make sure there is
no duplicated IP address by issuing a gratuitous ARP request to its only IP address. The Brocade
device will reply to this request because it is required under the Local Proxy ARP configuration.
When the host receives the ARP reply, the host incorrectly assumes that there is another host using
the same IP address.
A gratuitous ARP request packet is defined as an ARP request packet with the sender protocol
address that equals to the target protocol address. By disabling Gratuitous ARP Requests for Local
Proxy ARP, you are able to control whether to reply to gratuitous ARP requests under the Local Proxy
ARP configuration.
To enable the ignore-gratuitous-arp parameter when the ip local-proxy-arp command is turned on,
enter the following command.
Brocade(config-if-e1000-1/6)# ip local-proxy-arp ignore-gratuitous-arp
To disable only the ignore-gratuitous-arp parameter when the Local Proxy ARP is configured, enter
the following command.
Brocade(config-if-e1000-1/6)# no ip local-proxy-arp ignore-gratuitous-arp
To disable both the Local Proxy ARP command and the ignore-gratuitous-arp parameter, enter the
following command.
Brocade(config-if-e1000-1/6)# no ip-local-proxy-arp
Syntax: [no] ip local-proxy-arp [ignore-gratuitous-arp]
When using the no ip local-proxy-arp ignore-gratuitous-arp command, only the ignore-gratuitous-arp
parameter is turned off. The ip-local-proxy-arp command is still turned on.
The Brocade device drops all ARP packets that are sent from its own interface. When the
ignore-gratuitous-arp parameter is turned on, the Brocade device will not reply to a gratuitous ARP
request even if the target protocol address matches the configured interface IP address.