In this tutorial I will try to explain the different ways to set up frame-relay topologies in conjunction with OSPF. The topology I will use for this is the same one as I used before in the NTP and URPF posts.

For the most basic topology where R1 is the HUB and R2 en R3 are the spokes these configurations can be used :

R1 :
!
interface Serial1/0
ip address 10.10.10.1 255.255.255.0
encapsulation frame-relay
serial restart-delay 0
frame-relay map ip 10.10.10.2 102 broadcast
frame-relay map ip 10.10.10.3 103 broadcast
no frame-relay inverse-arp
!

R2 :
!
interface Serial1/0
ip address 10.10.10.2 255.255.255.0
encapsulation frame-relay
serial restart-delay 0
frame-relay map ip 10.10.10.1 201 broadcast
frame-relay map ip 10.10.10.3 201 broadcast
no frame-relay inverse-arp
!

R3 :
!
interface Serial1/0
ip address 10.10.10.3 255.255.255.0
encapsulation frame-relay
serial restart-delay 0
frame-relay map ip 10.10.10.1 301 broadcast
frame-relay map ip 10.10.10.2 301 broadcast
no frame-relay inverse-arp
!

The default network-type for Serial interfaces is Non-Broadcast. You can find this out by issueing the “sh ip ospf interface” command

R1#sh ip ospf interface ser1/0
Serial1/0 is up, line protocol is up
Internet Address 10.10.10.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DR, Priority 255
Designated Router (ID) 1.1.1.1, Interface address 10.10.10.1
No backup designated router on this network
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
oob-resync timeout 120
Hello due in 00:00:14
Supports Link-local Signaling (LLS)
Index 1/1, flood queue length 0
Next 0×0(0)/0×0(0)
Last flood scan length is 0, maximum is 0
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)

When configured like above the OSPF adjacencies will not be formed. For the network type NON_BROADCAST neighbors need to be specified. The network types Non Broadcast and Broadcast have a DR and BDR election. As you can see R1 is the HUB router and so we want this router the become the DR. To make R1 the DR I issued the command ” ip ospf priority 255″ under the physical interface. To make sure R2 and R3 will not become the DR you need to issue the command ” ip ospf priority 0″ under the physical interface.

The final configurations look like this :

R1 :
!
interface Serial1/0
ip address 10.10.10.1 255.255.255.0
encapsulation frame-relay
ip ospf priority 255
serial restart-delay 0
frame-relay map ip 10.10.10.2 102 broadcast
frame-relay map ip 10.10.10.3 103 broadcast
no frame-relay inverse-arp
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
network 10.10.10.1 0.0.0.0 area 0
neighbor 10.10.10.2
neighbor 10.10.10.3
!
R1#sh ip ospf nei

Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 0 FULL/DROTHER 00:01:43 10.10.10.2 Serial1/0
3.3.3.3 0 FULL/DROTHER 00:01:55 10.10.10.3 Serial1/0

R2 :
!
interface Serial1/0
ip address 10.10.10.2 255.255.255.0
encapsulation frame-relay
ip ospf priority 0
serial restart-delay 0
frame-relay map ip 10.10.10.1 201 broadcast
frame-relay map ip 10.10.10.3 201 broadcast
no frame-relay inverse-arp
!
router ospf 1
router-id 2.2.2.2
log-adjacency-changes
network 10.10.10.2 0.0.0.0 area 0
!
R2#sh ip ospf nei

Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 255 FULL/DR 00:01:57 10.10.10.1 Serial1/0

R3 :
!
interface Serial1/0
ip address 10.10.10.3 255.255.255.0
encapsulation frame-relay
ip ospf priority 0
serial restart-delay 0
frame-relay map ip 10.10.10.1 301 broadcast
frame-relay map ip 10.10.10.2 301 broadcast
no frame-relay inverse-arp
!
router ospf 1
router-id 3.3.3.3
log-adjacency-changes
network 10.10.10.3 0.0.0.0 area 0
!
R3#sh ip ospf nei

Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 255 FULL/DR 00:01:59 10.10.10.1 Serial1/0