Switch User Manual

22 An Introduction to IP Routing Protocols

Proxy Address Resolution Protocol (Proxy ARP)

Proxy ARP allows a network station to respond to an ARP request from a

locally attached host or end station for a remote destination. It does so by

sending an ARP response back to the local host with its own MAC address

of the network station interface for the subnet on which the ARP request

was received. The reply is generated only if the switch has an active route

to the destination network.

The ﬁgure below is an example of proxy ARP operation. In this example,

host C with a 24-bit mask appears to be locally attached to host B with a

16-bit mask, so host B sends an ARP request for host C. However, the 5500

Series switch is between the two hosts. To enable communication between

the two hosts, the 5500 Series switch would respond to the ARP request

with host C’s IP address but with its own MAC address.

Proxy ARP Operation

Static routes

Once routable VLANs are created though IP address assignment, static

routes can be created. Static routes allow for the manual creation of speciﬁc

routes to a destination IP address. Static routes can also be used to specify

a route to all networks for which there are no explicit routes in the Forwarding

Information Base or the routing table. This static default route is a route to

the network address 0.0.0.0 as deﬁned by the IEEE RFC 1812 standard.

Because of their static nature, this type of solution is not scalable. Thus,

in a large or growing network this type of route management may not be

desirable. Also, static routes do not have the capacity to determine the

failure of paths. Thus, a router can still attempt to use a path after it has

failed.

Nortel Ethernet Routing Switch 5500 Series

Conﬁguration-IP Routing Protocols

NN47200-503 03.01 Standard

5.1 27 August 2007