Icmp Router Discovery Protocol (Irdp) - Allied Telesis SwitchBlade x908 Series Software Reference Manual

Internet Protocol (IP) Addressing and Protocols
ICMP Router Discovery Protocol
(IRDP)
Router discovery Your device supports the router specification sections of RFC 1256, ICMP Router Discovery
Messages. If this feature is configured, your device sends router advertisements periodically and
in response to router solicitations. It does not support the Host Specification section of this
RFC.
Benefits Before an IP host can send an IP packet, the host has to know the IP address of a neighboring
router that can forward the packet to its destination. ICMP Router Discovery messages let
routers automatically advertise themselves to hosts. Other methods either require someone to
manually keep these addresses current, or require DHCP to send router addresses.
Router discovery The following table summarizes what happens when Router Discovery advertisements are
process enabled on an interface.
When...
Router Discovery advertising starts on an
interface because:
- your device starts up, or
- you enable advertisements on your device
or on an interface
a host starts up
your device receives a router solicitation
a host receives a router advertisement
the lifetimes of all existing router
advertisements on a host expire
a host does not receive a router
advertisement after sending a small number of
router solicitations
a host needs a default router address
Router Discovery advertising is deleted from
the interface
the router receives a router advertisement
from another router
Advertisement A router advertisement is an ICMP (type 10) message that contains the following:
messages
■
■
■
Your device does not send router advertisements by default.
22.10
in the destination address field of the IP header, the interface's configured advertisement
address, either 224.0.0.1 or 255.255.255.255.
in the lifetime field, the interface's configured advertisement lifetime.
in the Router Address and Preference Level fields, the addresses and preference levels of
all the logical interfaces that are set to advertise.
Software Reference for SwitchBlade® x908, x900 and x600 Series Switches
TM
AlliedWare Plus Operating System - Software Version 5.3.1
Then...
your device multicasts a router advertisement
and continues to multicast them periodically
until router advertising is disabled.
the host may send a router solicitation
message.
your device multicasts an early router
advertisement from the interface on which it
received the router solicitation.
the host stores the IP address and preference
level for the advertisement lifetime.
the host sends a router solicitation.
the host waits for the next unsolicited router
advertisement.
the host uses the IP address of the router or
L3 switch with the highest preference level.
your device multicasts a router advertisement
with the IP address(es) that stopped
advertising, and a lifetime of zero. It continues
to periodically multicast router advertisements
for other interfaces, if configured to.
the router does nothing but silently discards
the message
C613-50007-01 REV B