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Basic concepts
Preference of an IP address
Every IP address advertised in RAs has a preference value. The IP address with the highest preference is
selected as the default gateway address.
You can specify the preference for IP addresses advertised on a router interface.
A larger preference value represents a higher preference. The minimum preference value (-2147483648)
indicates that the address, even though it might be advertised, is not to be used by neighboring hosts as
a default gateway address.
Lifetime of an IP address
An RA contains a lifetime field that specifies the lifetime of advertised IP addresses. If no new RA for an
IP address is received within the lifetime of the IP address, the host removes the corresponding route entry.
All the IP addresses advertised by an interface have the same lifetime.
Advertising interval
A router interface with IRDP enabled sends out RAs at a random interval between the minimum
advertising interval and the maximum advertising interval. This mechanism prevents the local link from
being overloaded by a large number of RAs sent simultaneously from routers.
HP recommends that you shorten the advertising interval on a link that suffers high packet loss rates.
Destination address of RAs
An RA uses either of the following destination IP addresses:
• Broadcast address 255.255.255.255.
• Multicast address 224.0.0.1, which identifies all hosts on the local subnet.
By default, the destination IP address of an RA is the broadcast address. If the interface that sends RAs
supports multicast, specify 224.0.0.1 as the destination IP address.
Proxy-advertised IP addresses
By default, an interface advertises its primary and secondary IP addresses. You can specify IP addresses
of other gateways for an interface to proxy-advertise.
Protocols and standards
RFC 1256: ICMP Router Discovery Messages
Configuration procedure
To configure IRDP:
Ste
Command
Remarks
1. Enter system view.
system-view N/A
2. Enter interface view.
interface interface-type
interface-number
The interface can be a Layer 3
Ethernet interface or VLAN interface.
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