Alcatel-Lucent 6850-48 Guida Di Rete

Configuring RDP

RDP Overview

OmniSwitch AOS Release 6 Network Configuration Guide

page 29-5

End host (clients) sending traffic to other networks need to forward their traffic to a router. In order to do 
this, hosts need to find out if one or more routers exist on their LAN, then learn their IP addresses. One 
way to discover neighboring routers is to manually configure a list of router IP addresses that the host 
reads at startup. Another method available involves listening to routing protocol traffic to gather a list of 
router IP addresses.

RDP provides an alternative method for hosts to discover routers on their network that involves the use of 
ICMP advertisement and solicitation messages. Using RDP, hosts attached to

 

multicast or broadcast 

networks send solicitation messages when they start up. Routers respond to solicitation messages with an 
advertisement message that contains the router IP addresses. In addition, routers first send advertisement 
messages when their RDP interface becomes active, and then subsequently at random intervals.

When a host receives a router advertisement message, it adds the IP addresses contained in the message to 
its list of default router gateways in the order of preference. As a result, the list of router IP addresses is 
dynamically created and maintained, eliminating the need for manual configuration of such a list. In addi-
tion, hosts do not have to recognize many different routing protocols to discover router IP addresses.

The following diagram illustrates an example of using RDP in a typical network configuration:

When interfaces 2/3 and 2/4 on hosts H-1 and H-2, respectively, become active, they transmit router solic-
itation ICMP messages on Network 17.0.0.0. The RDP enabled routers RS-1 and RS-2 pick up these pack-
ets on their RDP interfaces 1/1 and 1/2 and respond with router advertisement ICMP messages. RS-1 and 
RS-2 also periodically send out router advertisements on their RDP interfaces.