The ipv6 summary command enables IS-IS IPv6 route summarization.
The undo ipv6 summary command disables IS-IS IPv6 route summarization.
By default, IS-IS IPv6 route summarization is disabled.
| Parameter | Description | Value |
|---|---|---|
| ipv6-address |
Specifies the address segment of the routes to be summarized. |
The value is a 32-digit hexadecimal number, in the format of X:X:X:X:X:X:X:X. |
| prefix-length |
Specifies the prefix length of a summary route. |
The value is an integer ranging from 0 to 128. |
| avoid-feedback |
Avoid learning your own published aggregation routes from another level. If there is a learning route in another level that is the same as the summary address, it is assumed that the route is infiltrated into another level and published by other devices after they have learned the summary route published by the local device. At this point, avoid-feedback occurs and the route becomes inactive, removed from the RM routing table. |
- |
| generate_null0_route |
Generates Null 0 routes to prevent routing loops. |
- |
| tag tag-value |
Specifies an administrative tag value. |
The value is an integer ranging from 1 to 4294967295. |
| learning-avoid-loop |
Generates a backup route for a summary route to prevent routing loops. |
- |
| level-1 |
Summarizes routes in the Level-1 area. |
- |
| level-2 |
Summarizes routes in the Level-2 area. If no level is specified, Level-2 routes are summarized. |
- |
| level-1-2 |
Summarizes routes in Level-1 and Level-2 areas. |
- |
Usage Scenario
The IS-IS routing table of a device on a medium or large IS-IS network contains a large number of routing entries. Storing the routing table consumes a large number of memory resources, and transmitting and processing routes consume lots of network resources. IS-IS route summarization can solve this problem.
Routes with the same IPv6 prefix can be summarized into one route. Route summarization on a large-scale IS-IS network reduces the number of routes in a routing table and minimizes system resource consumption. In addition, if a specific link frequently alternates between Up and Down, the links not involved in the route summarization will not be affected, which prevents route flapping and improves network security. Configuring route summarization does not affect the routing table on a local device. Each specific route is displayed in the routing table. Configuring route summarization, however, reduces LSPs to be flooded. Any device that receives the LSP from the summarization-capable router has only one summarized route in its routing table. On a network, at least two devices (A and B for example) advertise the same summary route. If device C preferentially selects the summary route advertised by device A and sends traffic destined for the address of a specific route that participated in summarization of the summary route, to device A, but the outbound interface of the specific route on device A fails, device C keeps sending the traffic to device A because device C fails to detect the fault in time. Due to the outbound interface failure, device A sends the traffic back to device C, leading to a routing loop. To prevent this problem, specify the learning-avoid-loop parameter when configuring the summary route on device A so that a backup path (passing through device B) is generated for the summary route.Prerequisites
An IS-IS process has been created using the isis command, and IPv6 has been enabled for this process using the ipv6 enable command.
Precautions