Multicast and Routing Guide K/KA/KB.15.15

9 ICMP Router Discovery Protocol
The ICMP Router Discovery Protocol (IRDP) is used by HP routing switches to advertise the IP
addresses of their router interfaces to directly attached hosts. IRDP is disabled by default. You can
enable the feature on a global basis or on an individual VLAN interface basis.
Configuring IRDP
When IRDP is enabled, the routing switch periodically sends Router Advertisement messages out
the IP interfaces on which the feature is enabled. The messages advertise the routing switch's IP
addresses to directly attached hosts who listen for the messages. In addition, hosts can be configured
to query the routing 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 HP routing switch, the routing switch responds to the Router Solicitation
messages. Some clients interpret this response to mean that the routing switch is the default gateway.
If another router is actually the default gateway for these clients, leave IRDP disabled on the HP
routing switch.
IRDP uses the following parameters. If you enable IRDP on individual VLAN interfaces, you can
configure these parameters on an individual VLAN interface basis.
Packet type The routing switch can send Router Advertisement messages
as IP broadcasts or as IP multicasts addressed to IP multicast
group 224.0.0.1. The default packet type is IP broadcast.
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.
Maximum message interval and
minimum message interval
When IRDP is enabled, the routing switch sends the Router
Advertisement messages every 450-600 seconds by default.
The time within this interval that the routing 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 routing 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.
Preference If a host receives multiple Router Advertisement messages
from different routers, the host selects the router that send
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
Enter the following command:
Configuring IRDP 225