15-17
IP Routing Features
Configuring IRDP
Configuring IRDP
The ICMP Router Discovery Protocol (IRDP) is used by HP routing switches
to advertise the IP addresses of its router interfaces to directly attached hosts.
IRDP is enabled by default. You can enable the feature on a global basis or on
an individual VLAN interface basis.
When IRDP is enabled, the routing switch periodically sends Router Adver-
tisement 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 inter-
face 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 about 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
!Software.book Page 17 Thursday, October 10, 2002 6:10 PM
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