Basic concepts
Preference of an IP address
Every IP address advertised in RAs has a preference value. A larger preference value represents a higher preference. The IP address with the highest preference is selected as the default gateway address.
You can specify the preference for IP addresses to be advertised on a router interface.
An address with the minimum preference value (-2147483648) will not be used 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 the host does not receive a new RA for an IP address within the address lifetime, the host removes the 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 randomly between the minimum and maximum advertising intervals. This mechanism prevents the local link from being overloaded by a large number of RAs sent simultaneously from routers.
As a best practice, 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 link.
By default, the destination IP address of an RA is the broadcast address. If all listening hosts in a local area network support IP 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.