Basic OSPF configuration over Frame Relay

Hi all,

I wanted to try to configure OSPF over a Frame Relay netowrk. Let's see how to  do it. For our lab we are considering the  following topology:

To start with we are only  use routers R2, R5 and R4. We are going to use a hub and spoke topology, where R4 is going to be the hub and R2 and R5 spokes.


Frame-Relay Configuration

Let's start with the Frame-Relay configuration on the Routers:

R2#interface Serial0/0 ip address 10.2.1.200 255.255.255.0 encapsulation frame-relay serial restart-delay 0 frame-relay interface-dlci 102

For the Hub router it is used mulitpoint subinterfaces which results in this configuration:

hostname(config)# R4#interface Serial0/0 no ip address encapsulation frame-relay serial restart-delay 0 ! interface Serial0/0.201 multipoint ip address 10.2.1.1 255.255.255.0 frame-relay interface-dlci 201 ! interface Serial0/0.204 multipoint ip address 10.4.1.1 255.255.255.0 frame-relay interface-dlci 204

We can now verify the frame-relay map is up and we can ping from one router to another. As a example, dynamic map is established in router R4:

  The ping from R5 reaches R4 correctly.

OSPF Neighbor Configuration

Once the frame relay netwok is configured and connectivity is verified, it's time to configure ospf. We are just going to make a very easy configuration:

R2#sh run | sec router router ospf 1 log-adjacency-changes network 10.2.1.0 0.0.0.255 area 0

R4#sh run | sec router router ospf 1 log-adjacency-changes network 10.2.1.0 0.0.0.255 area 0 network 10.4.1.0 0.0.0.255 area 1

After configuring the ospf routing process in both routes we should expect they become neighbors. Unfortunately nothing happens. We can find the reason why with the show ip ospf interface serial0/0 command.

 


 The network type is NON_BROADCAST, so no broadcast and mulitcast packets are allowed the interface. For the adjancecy to be form between the 2 routes, one of router needs to send a mulitcast hello packet to the ip 224.0.0.5.

To change that behavior we make use of the ip ospf network broadcast interface command.

R2#sh run | sec interface interface Serial0/0 ip address 10.2.1.200 255.255.255.0 encapsulation frame-relay ip ospf network broadcast serial restart-delay 0 frame-relay interface-dlci 102

Alternatively because we were talking of a non-broadcast network, we could use configure the neighbors manually so we would no need multicast packets to form the adjacency.

Once modified the network type, we can see the packets coming out the interface:

*Mar 1 03:11:35.943: OSPF: Send hello to 224.0.0.5 area 0 on Serial0/0 from 10.2.1.200 *Mar 1 03:11:45.947: OSPF: Send hello to 224.0.0.5 area 0 on Serial0/0 from 10.2.1.200

Although now packets are now being sent, we are still not having the full adjacency. Debugging ospf we should us the reason:

*Mar 1 05:16:32.574: OSPF: Rcv hello from 10.2.1.200 area 0 from Serial0/0.201 10.2.1.200 *Mar 1 05:16:32.578: OSPF: Mismatched hello parameters from 10.2.1.200 *Mar 1 05:16:32.582: OSPF: Dead R 40 C 120, Hello R 10 C 30 Mask R 255.255.255.0 C 255.255.255.0

The hello parameters mismatches because we changes the network type in one router but we forgot to do it in the other one. If we changed in the other router to broadcast, the hello parameters we will be the same

*Mar 1 06:39:52.870: %OSPF-5-ADJCHG: Process 1, Nbr 10.2.1.200 on Serial0/0.201 from LOADING to FULL, Loading Done

Another option is to change manually the hello timers using the commands ip ospf hello-interval and ip ospf dead-interval.