BigIron RX Series Configuration Guide 20753-1001810-01Configuring forwarding parameters 7Some types of hosts use the Router Solicitation messages to discover their default gateway. WhenIRDP is enabled, the device responds to the Router Solicitation messages. Some clients interpretthis response to mean that the device is the default gateway. If another router is actually thedefault gateway for these clients, leave IRDP disabled on the device.IRDP uses the following parameters. If you enable IRDP on individual ports rather than globally,you can configure these parameters on an individual port basis using:• Packet type – The device can send Router Advertisement messages as IP broadcasts or as IPmulticasts 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, thedevice sends the Router Advertisement messages every 450 – 600 seconds by default. Thetime within this interval that the device selects is random for each message and is not affectedby traffic loads or other network factors. The random interval minimizes the probability that ahost will receive Router Advertisement messages from other routers at the same time. Theinterval on each IRDP-enabled device interface is independent of the interval on otherIRDP-enabled interfaces. The default maximum message interval is 600 seconds. The defaultminimum message interval is 450 seconds.• Hold time – Each Router Advertisement message contains a hold time value. This valuespecifies the maximum amount of time the host should consider an advertisement to be validuntil 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 thehold time for an advertisement expires, the host can reasonably conclude that the routerinterface that sent the advertisement is no longer available. The default hold time is threetimes the maximum message interval.• Preference – If a host receives multiple Router Advertisement messages from differentrouters, the host selects the router that sent the message with the highest preference as thedefault gateway. The preference can be a number from 4294967296 to 4294967295. Thedefault is 0.Enabling IRDP globallyTo globally enable IRDP, enter the following command.BigIron RX(config)# ip irdpThis command enables IRDP on the IP interfaces on all ports. Each port uses the default values forthe IRDP parameters. The parameters are not configurable when IRDP is globally enabled.Enabling IRDP on an individual portTo enable IRDP on an individual interface and change IRDP parameters, enter commands such asthe following.BigIron RX(config)# interface ethernet 1/3BigIron RX(config-if-e10000-1/3)# ip irdp maxadvertinterval 400This example shows how to enable IRDP on a specific port and change the maximumadvertisement interval for Router Advertisement messages to 400 seconds.NOTETo enable IRDP on individual ports, you must leave the feature globally disabled.
