partition avoidance area-tag
no partition avoidance area-tag
area-tag Meaningful name for a routing process. If it is not specified, a null tag is assumed and the process is referenced with a null tag. This name must be unique among all IP or Connectionless Network Service Protocol (CLNS) router processes for a given router.
Required for multiarea IS-IS configuration. Optional for conventional IS-IS configuration.
To cause an IS-IS Level 1-2 border router to stop advertising the Level 1 area prefix into the Level 2 backbone when full connectivity is lost between the border router, all adjacent Level 1 routers, and end hosts, use the partition avoidance command in router configuration mode. To disable this output format, use the no form of the command.
This command is disabled by default.
When the partition avoidance command is enabled, a multiarea router withdraws a Level 1 area prefix from the Level 2 backbone when it no longer has any active adjacencies to that Level 1 area. This withdrawal prevents the Level 1 area from appearing to be partitioned within the Level 2 backbone.
In International Standards Organization (ISO) CLNS networks using a redundant topology, it is possible for an area to become "partitioned" when full connectivity is lost between a Level 1-2 border router, all adjacent Level 1 routers, and end hosts. In such a case, multiple Level 1-2 border routers advertise the Level 1 area prefix into the backbone area, even though any one router can reach only a subset of the end hosts in the Level 1 area.
When enabled, the partition avoidance command prevents this partitioning by causing the border router to stop advertising the Level 1 area prefix into the Level 2 backbone. This command displays the output from different areas as a string or additional white space.
Other cases of connectivity loss within the Level 1 area itself are not detected or corrected by the border router, and this command will have no effect.
The following example causes the routing process named Finance to stop advertising the prefix for the area named area1 when the router no longer has any active adjacencies to area1:Router(config)#router isis Finance Router(config-router)# partition avoidance area1
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