Connecting Enterprise hub to other enterprise spokes over NBMA (frame-relay)

The original design intention is not to advertise routes using ospf over NBMA network, it is not necessary for this case. However for Buona Vista HQ to be able to reach the two sites, I need entries in the routing table to let other routers know the road map to reach. A way is to let OSPF advertise a default route by using default-information originate always command, this diagram is very straightforward as there’s only one exit point out.

Two ways for 2651-3 to advertise default route

1. If 2651-3 (advertising router) has a default route, advertise the default route within ospf process using default-information originate command.

ip route Serial0/0.102

router ospf 1
default-information originate

2. The alternative way is to advertise default route irregardless whether 2651-3 (advertising router) has the default route or not this is accomplished by including the keyword always at the end of default-information originate command.

2651-3(config-router)#default-information originate always

(2651-3 has no default route configured, however this command will tell all SPF routers to send anything that they do not know to 2651-3)


1841-1 routing table

1841-1#sh ip route ospf is subnetted, 1 subnets
O [110/2] via, 09:36:50, FastEthernet0/0 is subnetted, 1 subnets
O [110/2] via, 09:42:42, FastEthernet0/1 is subnetted, 1 subnets
O IA [110/3] via, 07:49:48, FastEthernet0/0 is subnetted, 3 subnets
O [110/51] via, 07:29:41, FastEthernet0/1
[110/51] via, 07:29:51, FastEthernet0/0 is subnetted, 2 subnets
O IA [110/2] via, 07:50:53, FastEthernet0/0
O IA [110/2] via, 07:51:25, FastEthernet0/1
O*E2 [110/1] via, 00:02:49, FastEthernet0/1
[110/1] via, 00:02:49, FastEthernet0/0

The default metric type is E2 which is not incremental. If a destination ip subnet is unknown by 1841-1, it will send it to 2651-3.


Configuration to connect Campus cores via FR

router ospf 1
redistribute connected
network area 1
network area 1
network area 2
default-information originate always

interface Serial0/0.102 multipoint
ip address
frame-relay map ip 102 broadcast
frame-relay map ip 103 broadcast


ip route

interface Serial0/0.301 multipoint
ip address
frame-relay map ip 301 broadcast
frame-relay map ip 301


ip route

interface Serial0/0.201 multipoint
ip address
frame-relay map ip 201 broadcast
frame-relay map ip 201


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