default-information originate (OSPF)
To generate a default external route into an OSPF routing domain, use the default-information originate command in router configuration mode
Whenever you use the redistribute or the default-information
router configuration command to redistribute routes into an OSPF
routing domain, the Cisco IOS software automatically becomes an
Autonomous System Boundary Router (ASBR). However, an ASBR does not, by
default, generate a default route into the
OSPF routing domain. The software still must have a default route for
itself before it generates one, except when you have specified the always keyword
and this:
-
If the ASBR already has the default route in its routing table, you
can advertise the existing 0.0.0.0/0 into the OSPF domain with the default-information originate router configuration command.
-
If the ASBR doesn't have a default route, you can add the keyword always to the default-information originate command (default-information originate always).
This command will advertise a default route into the OSPF domain, regardless of whether it has a route to 0.0.0.0. Another benefit of adding always keyword is that it can add stability to the internetwork. For example, if the ASBR is learning a default route from another routing domain such as RIP and this route is flapping, then without the always keyword, each time the route flaps, the ASBR will send a new Type 5 LSA into the OSPF domain causing some instability inside the OSPF domain. With the always keyword, the ASBR will advertise the default inside the OSPF domain always, and thus the flapping of the default route from the RIP domain will not cause any instability inside the OSPF domai
