Configuring Irdp - Foundry Networks Switch and Router Installation And Configuration Manual

Foundry Switch and Router Installation and Configuration Guide

Configuring IRDP

The ICMP Router Discovery Protocol (IRDP) is used by Foundry Layer 3 Switches to advertise the IP addresses
of its router interfaces to directly attached hosts. IRDP is disabled by default. You can enable the feature on a
global basis or on an individual port basis.
• If you enable the feature globally, all ports use the default values for the IRDP parameters.
• If you leave the feature disabled globally but enable it on individual ports, you also can configure the IRDP
parameters on an individual port basis.
NOTE: You can configure IRDP parameters only an individual port basis. To do so, IRDP must be disabled
globally and enabled only on individual ports. You cannot configure IRDP parameters if the feature is globally
enabled.
When IRDP is enabled, the Layer 3 Switch periodically sends Router Advertisement messages out the IP
interfaces on which the feature is enabled. The messages advertise the Layer 3 Switch's IP addresses to directly
attached hosts who listen for the messages. In addition, hosts can be configured to query the Layer 3 Switch for
the information by sending Router Solicitation messages.
Some types of hosts use the Router Solicitation messages to discover their default gateway. When IRDP is
enabled on the Foundry Layer 3 Switch, the Layer 3 Switch responds to the Router Solicitation messages. Some
clients interpret this response to mean that the Layer 3 Switch is the default gateway. If another router is actually
the default gateway for these clients, leave IRDP disabled on the Foundry Layer 3 Switch.
IRDP uses the following parameters. If you enable IRDP on individual ports instead of enabling the feature
globally, you can configure these parameters on an individual port basis.
• Packet type – The Layer 3 Switch can send Router Advertisement messages as IP broadcasts or as IP
multicasts addressed to IP multicast group 224.0.0.1. The packet type is IP broadcast.
• Maximum message interval and minimum message interval – When IRDP is enabled, the Layer 3 Switch
sends the Router Advertisement messages every 450 – 600 seconds by default. The time within this interval
that the Layer 3 Switch selects is random for each message and is not affected by traffic loads or other
network factors. The random interval minimizes the probability that a host will receive Router Advertisement
messages from other routers at the same time. The interval on each IRDP-enabled Layer 3 Switch interface
is independent of the interval on other IRDP-enabled interfaces. The default maximum message interval is
600 seconds. The default minimum message interval is 450 seconds.
• Hold time – Each Router Advertisement message contains a hold time value. This value specifies the
maximum amount of time the host should consider an advertisement to be valid until a newer advertisement
arrives. When a new advertisement arrives, the hold time is reset. The hold time is always longer than the
maximum advertisement interval. Therefore, if the hold time for an advertisement expires, the host can
reasonably conclude that the router interface that sent the advertisement is no longer available. The default
hold time is three times the maximum message interval.
• Preference – If a host receives multiple Router Advertisement messages from different routers, the host
selects the router that sent the message with the highest preference as the default gateway. The preference
can be a number from -4294967296 to 4294967295. The default is 0.
Enabling IRDP Globally
To enable IRDP globally, use either of the following methods.
USING THE CLI
To globally enable IRDP, enter the following command:
BigIron(config)# ip irdp
This command enables IRDP on the IP interfaces on all ports. Each port uses the default values for the IRDP
parameters. The parameters are not configurable when IRDP is globally enabled.
15 - 66 December 2000