OSPF in FR

Answered Question
Oct 11th, 2009

Hi Experts,

I am doing the below scenario in a Lab environment and now I expect your help in understanding the Framerelay behaviour with OSPF

I have Cisco Router HUB,SPOKE-1,SPOKE-2 connected each other in a Fram relay cloud. HUB router is configured as hub/Core router and othe 2 routers are connected to HUB router using serial interface. It is a point to multipoint setup where HUB router is configured with ip address and dlci parameters in physical interface itself. OSPF is running in al the routers and OSPF interface is configured as BROADCAST

HUB:

int ser 0/0

ip add 192.168.1.1 255.255.255.0

encap frame-relay

ip ospf network broadcast

ip ospf priority 100

So what I am trying to achieve is this HUB router will be the OSPF DR. This works perfectly as long as HUB router interface goes down.

When HUB router serial interface goes down, SPOKE-2 becomes the DR (due to the Highest IP address). HUB router is not becoming DR back even when its serial interface comes up ( I know it the OSPF behaviour by default to maintain the stability in the network).

Thus, HUB router is not having the routes of network SPOKE-1 & behind SPOKE-1. I think since Drother Router will talk to DR and advertise its route to DR only and not BDR and other DR.

If I manually clear ospf process then things becoming alright (HUB becomes DR back)

Is this the normal problem. Is there any workaround available.

Thanks for readin this lenghthy post and kindly reply with your expertised solution

Thanks in advance

sairam

I have this problem too.
0 votes
Correct Answer by Hitesh Vinzoda about 7 years 1 month ago

Hi Sairam,

The DR election in OSPF is non-preemptive. This means the when the DR is down or not reachable for some reason. the BDR takes the role of DR. When the DR comes up it will not take back the role of DR, thus creating the problem.

Even if you give the ospf priority of interface to 100, It will not preempt. It is normal problem. In your case if the FR is partial mesh than i suggest that you configure priority of zero (0) on the spoke's ospf interfaces ( if you want the network to be a BROADCAST network). This will make sure that Spokes never will be DR. Or else change the Ospf network type to prevent the election of DR/BDR.

Regards

Hitesh Vinzoda

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Correct Answer
Hitesh Vinzoda Sun, 10/11/2009 - 04:54

Hi Sairam,

The DR election in OSPF is non-preemptive. This means the when the DR is down or not reachable for some reason. the BDR takes the role of DR. When the DR comes up it will not take back the role of DR, thus creating the problem.

Even if you give the ospf priority of interface to 100, It will not preempt. It is normal problem. In your case if the FR is partial mesh than i suggest that you configure priority of zero (0) on the spoke's ospf interfaces ( if you want the network to be a BROADCAST network). This will make sure that Spokes never will be DR. Or else change the Ospf network type to prevent the election of DR/BDR.

Regards

Hitesh Vinzoda

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