OSPF releases default routes

When you debug the network, you cannot learn the default route when using show ip route, because redistribute static subnets can only publish non-default static routes.

How does OSPF generate default routes?

1. default-information originate

Purpose: Enable ospf to broadcast the default route 0.0.0.0 to the ospf domain. If route 0.0.0.0 exists in the local ip Route Selection table, this command can broadcast the route. If it does not exist, it cannot be broadcast.

1. default-information originate always

Purpose: Enable ospf to broadcast the default route 0.0.0.0 to the ospf domain. Even if route 0.0.0.0 does not exist in the local ip Route Selection table, this command also broadcasts the default route. If the keyword always is not used and the default route is flapping, ospf needs to send an update to the ospf domain each time the default jitter occurs. If the default route is jittery, using the keyword always will reduce the operation on the ospf database to ensure the stability of the ospf database.

2. default-information originate metric cost

3. default-information originate always metric cost

Cost-metric Cost of the external default route to be broadcast. The value range is 0 ~ 1677214 purpose: Set the external cost of the default route for ospf domain broadcasting. The first form of the command only broadcasts the default route when the route exists in the local ip Route Selection table. The second form is the unconditional broadcast default route. Meitric can be used to select a better default route if the ospf router broadcasts more than the default route. The default route with the lowest meitric is considered as the best route.

4. default-information originate metric-type

5. default-information originate always metric-type

Type -- the cost of type 1 route can be set to 1 or 2. The cost of type 1 route includes the external cost and ospf cost of Route distribution again. The cost of Type 2 routing can only include the external cost. The default value is type 2. Purpose: When a route is distributed to ospf again, the route is allocated to a measurement that indicates the cost from ASBR to this route. If the default route is broadcast as the type 2 route (default), the cost of the default route should be 1 for each router in the ospf domain. if the default router Europe is used as the type 1 route for broadcast, the cost of the default route will include the internal cost of reaching the ASBR and the external cost of the route set by the ASBR. If multiple ASBR paths exist in the ospf domain, all routes will have the same cost when they are broadcast as type 2. If the default route is used as the type 1 route broadcast, ospf can determine the optimal path to reach the ASBR.

6. default-information originate route-map-name

Route-map-name -- ospf generates a default route only when the condition of route-map is met. If you use the keyword always, the default route will be broadcast, regardless of the condition and purpose of route-map: the broadcast of the default route can be implemented using the route-map conditional. If the condition of route-map is met, the default route will be broadcast to the ospf domain.