Using the defaultinformation originate Command

OSPF does not support redistribution of statically defined default routes. Instead, OSPF requires the default-information originate router subcommand, which essentially tells OSPF to redistribute any default routes found in the routing table, either static routes or routes from another routing protocol. The following list summarizes the default routing features when using the default-information originate command with OSPF:

Redistributes any default route (0.0.0.0/0) in the routing table.

The command can set the metric and metric type directly, with OSPF defaulting to cost 1 and type E2.

OSPF allows the use of the always keyword, which means a default is sourced regardless of whether a default route is in the routing table.

Not supported by EIGRP.

Supported by RIP, with some differences. (Refer to the text following Example 11-9 for an explanation of the differences.)

Example 11-9 shows an example of using the default-information originate command with OSPF. In this case, R1 has learned a route to 0.0.0.0/0 via BGP from R9 in Figure 11-8.

Example 11-9 Static Default Route with Route Redistribution router ospf 1 network 15.0.0.0 0.255.255.255 area 0 default-information originate

! R5 has a default route, defaulting to type E2, cost 1. It as advertised as a

R5# show ip route ospf

O*E2 0.0.0.0/0 [110/1] via 15.1.1.1, 00:18:07, Serial0/0.1 R5# sh ip ospf data | begin Type-5

Type-5 AS External Link States

Link ID ADV Router Age Seq# Checksum Tag

0.0.0.0 1.1.1.1 1257 0x80000001 0x008C12 1

As mentioned earlier, RIP does support the default-information originate command; however, the command behaves slightly differently in RIP than it does in OSPF. With RIP, this command creates and advertises a default route if either no default route exists or a default route was learned from another routing protocol. However, if a static route to 0.0.0.0/0 is in the local routing table, the default-information originate command does not cause RIP to inject a default—the reason behind this behavior is that RIP already supports redistribution of static routes, so redistribute static should be used in that case.

Continue reading here: Using the ip defaultnetwork Command

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