Configuring OSPF to Advertise a Default Route to OSPF Areas
Context
In a routing table, a default route is the route with both the destination and mask being 0.0.0.0. You can run the display ip routing-table command to check whether a default route is configured. If the destination address of a packet does not match any entry in the routing table, the packet is sent using a default route. If the destination address of a packet does not match any entry in the routing table and no default route exists, the packet is discarded. An Internet Control Message Protocol (ICMP) packet is then sent, informing the originating host that the destination host or network is unreachable.
Procedure
- Configuring OSPF to advertise a default route to OSPF areas
- Run the following commands as required:
Run default-route-advertise [ [ always | permit-calculate-other ] | cost cost | type type | route-policy route-policy-name | distribute-delay delay-time ] *
Or run default-route-advertise [ permit-calculate-other | cost cost | type type | route-policy route-policy-name | distribute-delay delay-time | permit-ibgp ] *
OSPF is configured to advertise a default route to OSPF areas.
- always: indicates that an LSA describing a default route is generated and then advertised regardless of whether there are active default routes of other OSPF processes in the routing table of the local device.
- permit-calculate-other: indicates that the local router is still allowed to calculate the default routes advertised by other switches after adverting its default route.
- route-policy route-policy-name: indicates that, when there are matched default routing entries generated by other OSPF processes in the routing table of the local device, the local device advertises default routes according to the parameters in a configured routing policy.
Run default-route-advertise summary cost cost
The default cost of a summary LSA (Type 3 LSA) is set.
Before setting the parameter, you need to configure VPN information. Otherwise, this command cannot be run.
- An ASE LSA that describes a default route is generated and then advertised only when there are active default routes of other OSPF processes in the routing table of the local device.
- Before advertising a default route, OSPF compares the preferences of default routes. Therefore, if a static default route is configured on an OSPF switch, to add the default route advertised by OSPF to the current routing table, ensure that the preference of the configured static default route is lower than that of the default route advertised by OSPF.
- Run the following commands as required:
