summary (IS-IS)
Function
The summary command configures IS-IS to summarize routes.
The undo summary command cancels route summarization.
By default, IS-IS does not summarize routes.
Format
summary ip-address mask [ avoid-feedback | generate_null0_route | tag tag | [ level-1 | level-1-2 | level-2 ] ] *
summary ipv6-address mask [ avoid-feedback | generate_null0_route | tag tag | [ level-1 | level-1-2 | level-2 ] ] *
undo summary ip-address mask [ level-1 | level-1-2 | level-2 ]
undo summary ipv6-address mask [ level-1 | level-1-2 | level-2 ]
Parameters
| Parameter | Description | Value |
|---|---|---|
| ip-address | Specifies the address segment of the routes to be summarized. It is in dotted decimal notation. | The value is in dotted decimal notation. |
| mask | Specifies the summarized route mask in dotted decimal notation. | The value is in dotted decimal notation. |
| avoid-feedback | Avoids learning the summarized route through SPF calculation. | - |
| generate_null0_route | Generates the Null 0 route to avoid routing loops. | - |
| tag tag | Specifies the administrative tag value. |
The value is an integer ranging from 1 to 4294967295. |
| level-1 | Summarizes the routes on Level-1. | - |
| level-1-2 | Summarizes the routes both on Level-1 areas and on backbone network. | - |
| level-2 | Summarizes the routes only on the backbone network. | - |
| ipv6-address | Specifies the address segment of the routes to be aggregated. | - |
If the level is not specified, then level-2 is considered as default value.
Usage Guidelines
Usage Scenario
On a large-scale IS-IS network, you can configure route summarization to reduce the number of IS-IS routes in the routing table. This saves system resources and does not affect system performance.
If a specific link connected to a device within an IP address range that has been summarized alternates between Up and Down continually, the link status change will not be advertised to the devices that are not within the IP address range. This prevents route flapping and improves network stability.
Prerequisites
IS-IS processes have been enabled.
Configuration Impact
Configuring route summarization does not affect the routing table on a local device. Every specific route will be displayed in the routing table. Configuring route summarization, however, reduces LSPs to be flooded. Any device that has received the LSP has only one summarized route in its routing table. The devices except that directly connected to the device within the IP address range that has been summarized still has every specific route in its routing table.
Precautions
The summary ip-address mask [ avoid-feedback | generate_null0_route | tag tag | [ level-1 | level-1-2 | level-2 ] ] * command is used to configure the route summarization in an IPv4 base topology or an IPv4 topology instance.
The summary ipv6-address mask [ avoid-feedback | generate_null0_route | tag tag | [ level-1 | level-1-2 | level-2 ] ] * command is used to configure the route summarization in an IPv6 topology instance.
The ipv6 summary ipv6-address prefix-length [ avoid-feedback | generate_null0_route | tag tag | [ level-1 | level-1-2 | level-2 ] ] * command is used to configure the route summarization in an IPv6 base topology.
The routes to be summarized can be the IS-IS routes or the routes imported from other routing protocols. The cost of the summarized route is the smallest cost of the route that is summarized.
Example
# Set a summarized route 2.0.0.0/8.
<sysname> system-view
[sysname] isis
[sysname-isis-1] summary 2.0.0.0 255.0.0.0
<sysname> system-view
[sysname] isis 1
[sysname-isis-1] topology red topology-id 10
[sysname-isis-1-topology-red] summary 2.0.0.0 255.0.0.0