Timing Router Advertisements and Lifetimes
To configure the interval between IPv6 router advertisement transmissions on an interface, use the ipv6 nd ra-interval command in interface configuration mode.
Router (config-if)# ipv6 nd ra-interval seconds
The interval between transmissions defaults to 200 seconds. It should be less than or equal to the IPv6 router advertisement lifetime if the router is configured as a default router by using the ipv6 nd ra- lifetime command. To prevent synchronization with other IPv6 nodes, randomly adjust the actual value used to within 20 percent of the specified value.
To configure the “router lifetime” value in IPv6 router advertisements on an interface, use the ipv6 nd ra-lifetime command in interface configuration mode.
Router (config-if)# ipv6 nd ra-lifetime seconds
The “router lifetime” value defaults to 1800 seconds and is included in all IPv6 router advertisements sent out the interface. The value indicates the usefulness of the router as a default router on this interface. Setting the value to 0 indicates that the router should not be perceived a default router on this interface. The “router lifetime” value can be set to a non zero value to indicate that it should be considered a default router on this interface. The non zero value for the “router lifetime” value should not be less than the router advertisement interval.
To configure the amount of time that a remote IPv6 node is considered reachable, after some reachability confirmation event has occurred, use the ipv6 nd reachable-time command in interface configuration mode.
Router (config-if)# ipv6 nd reachable-time milliseconds
As a default 0 milliseconds (unspecified) is advertised in router advertisements and the value 30000
(30 seconds) is used for the neighbour discovery activity of the router itself.
The configured time enables the router to detect unavailable neighbors. Shorter configured times enable the router to detect unavailable neighbors more quickly; however, shorter times consume more IPv6 network bandwidth and processing resources in all IPv6 network devices. Very short configured times are not recommended in normal IPv6 operation.
The configured time is included in all router advertisements sent out of an interface so that nodes on the same link use the same time value. A value of 0 means indicates that the configured time is unspecified by this router.
Examples
a) The following example includes the IPv6 prefix 2001:0DB8::/64 in router advertisements sent out Ethernet interface 0/0 with a valid lifetime of 1000 seconds, a preferred lifetime of 900 seconds, and both the “onlink” and “autoconfig” flags set:
Router(config)# interface ethernet 0/0
Router(config-if)# ipv6 nd prefix 2001:0DB8::/64 1000 \\
900 onlink autoconfig
b) The following example configures an IPv6 router advertisement interval of 201 seconds for Ethernet interface 0/0:
Router(config)# interface ethernet 0/0
Router(config-if)# ipv6 nd ra-interval 201
c) The following example configures an IPv6 router advertisement lifetime of 1801 seconds for Ethernet interface 0/0:
Router(config)# interface ethernet 0/0
Router(config-if)# ipv6 nd ra-lifetime 1801
d) The following example configures an IPv6 reachable time of 1,700,000 milliseconds for Ethernet interface 0/0:
Router(config)# interface ethernet 0/0
Router(config-if)# ipv6 nd reachable-time 1700000