Configuring Default Routes

You can specify a default route within IS-IS routing domains. You can also suppress the installation of a default route to level 1-2 routers by level 1 routers.

Optionally, when you issue the default-information originate command and specify a route map, you can use the map to set a route tag for the default route. Make sure the route map you specify includes the set tag command, which defines a tag value for the default route within the IS-IS domain. For details about configuring and using route maps, see JUNOSe IP Services Configuration Guide.

default-information originate

• Use to generate a default route into an IS-IS routing domain.
• When you specify a route map with this command and the router has a route to 0.0.0.0 in the routing table, IS-IS originates an advertisement for 0.0.0.0 in its LSPs.
• When you do not specify a route map, the default route is advertised only in level 2 LSPs.
• If you specify a route map, you can use the map to set a route tag for the default route.
• For level 1 routing, look for the closest level 1-2 router to find the default route. The closest level 1-2 router is found by looking at the attach bit (ATT) in level 1 LSPs.
• The default value is disabled.
• Example1

  host1(config-router)#default-information originate

• Example 2

  host1(config-router)#default-information originate route-map map3

• Use the no version to disable the command.
• See default-information originate

suppress-default

• Use to prevent level 1 routers from automatically installing a default route to a level 1-2 router in order to reach destinations outside the area.
• Suppresses the level 1-2 router from indicating to level 1 routers that it can reach other areas. Consequently, the level 1 routers do not consider the level 1-2 router to be the nearest attached level 2 router and do not install default routes to it.
• This command is useful, for example, if you issue the distribute-domain-wide command, which causes the level 2 routes to be leaked into the level 1 area. The level 1 routers then have knowledge of the routes outside the area and will not need to rely on the nearest attached level 2 router for any unknown destination.
• Example

  host1(config-router)#suppress-default

• Use the no version to disable suppression of default routes.
• See suppress-default

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