Configuring Irdp; Overview; Irdp Operation - HP 6125XLG Layer 3-Ip Services Configuration Manual

Configuring IRDP

The term router in this chapter refers to a routing-capable device.
The term host in this chapter refers to the host that supports IRDP. For example, a host that runs the Linux
operating system.
NOTE:
The term "interface" in this chapter collectively refers to VLAN interfaces and Layer 3 Ethernet interfaces.
You can set an Ethernet port as a Layer 3 interface by using the port link-mode route command (see
2—LAN Switching Configuration Guide

Overview

ICMP Router Discovery Protocol (IRDP), an extension of the ICMP, allows hosts to discover the IP
addresses of neighboring routers that can be used as a default gateway to reach IP-based devices on
other networks.
IRDP provides the following benefits:
Enables hosts to track dynamic changes in router availability.
•
Is independent of any routing protocol.
•
Requires a minimal amount of manual configuration.
•

IRDP operation

IRDP uses the following types of ICMP messages:
Router advertisement (RA)—Sent by a router to advertise IP addresses (including the primary and
•
secondary IP addresses) and preference.
Router solicitation (RS)—Sent by a host to request the IP addresses of routers on the subnet.
•
A router periodically broadcasts or multicasts an RA message from each IRDP-enabled interface,
advertising the IP addresses of that interface. Hosts listen for RAs to obtain the IP addresses of
neighboring routers. Upon receiving an RA, the host adds the IP addresses in the RA to its routing table.
The host selects the IP address with the highest preference as the default gateway.
When a host attached to the subnet starts up, the host multicasts an RS message to request immediate
advertisements. If the host does not receive any advertisements to the RS, it retransmits the RS several
times. If the host does not discover the IP addresses of neighboring routers because of network problems,
the host can still discover them from periodic RAs.
IRDP allows hosts to discover the IP addresses of neighboring routers, but it does not suggest the best
route to a specific destination. If a host selects a router that is not the best next hop to a specific
destination, the router will send an ICMP redirect message to the host to provide a better route.
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