Proxy Arp - Alcatel-Lucent 7705 Configuration Manual

The configurable ARP retry timer is supported on VPRN and IES service interfaces, as well
on the router interface.

Proxy ARP

Proxy ARP is a technique by which a router on one network responds to ARP requests
intended for another node that is physically located on another network. The router
effectively pretends to be the destination node by sending an ARP response to the originating
node that associates the router's MAC address with the destination node's IP address (acts as
a proxy for the destination node). The router then takes responsibility for routing traffic to the
real destination.
Proxy ARP simplifies networking schemes because it enables nodes on a subnet to reach
remote subnets without the need to configure routing or a default gateway.
The 7705 SAR supports both proxy ARP and local proxy ARP. Local proxy ARP is similar
to proxy ARP except that it is used within a subnet; the router responds to all requests for IP
addresses within the subnet and forwards all traffic between the hosts in the subnet. Local
proxy ARP is used on subnets where hosts are prevented from communicating directly.
Typically, routers support proxy ARP only for directly attached networks. The 7705 SAR
supports proxy ARP for all known networks in the routing instance where the virtual interface
proxy ARP is configured.
Proxy ARP is supported on:
A typical application for proxy ARP is when hosts in a private subnet need to communicate
to host/servers via the public Internet; for example, when using network address translation
(NAT). Source NAT can be used for creating connections from inside (private network) to
outside (public network). If an arriving IP packet on the 7705 SAR matches the NAT policy
rules, an internal mapping is created between the private source IP address/source port and a
public source IP address/source port. The public IP address and port are configured in the
NAT pool policy.
Proxy ARP is therefore required for Source NAT when the NAT pool uses a range of IP
public addresses. The NAT pool public IP address can either be in a different subnet than the
public interface or in the same subnet as the public interface. Proxy ARP can be used to
respond to ARP requests for an IP address in these NAT pools.
7705 SAR OS Router Configuration Guide
• the global routing table
• IES service interfaces
• VPRN service interfaces
IP Router Configuration
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