OSPF Question

Answered Question
Feb 27th, 2007

Hi all,

I am in the process of designing a MPLS network. I understand that one router will become the PE, and my ABR will act as the CE. Behind CEs, there are different OSPF areas. However, these different OSPF areas have backup links connecting between them. How do I configure this backup link? Use Virtual link or Sham link or there are other ways? Please let me know. Thanks.

I have this problem too.
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Correct Answer by kunalpurk about 9 years 6 months ago

See....in this case , you will have to configure 2 virtual links to maintain full recahability between the routers in case of any link failures.

In case the link between PE2 and Router2 fails:-

============================================

One virtual links has to be created in the router configured in Area 2 with Transit area as Area 1 peering with the PE1.PE1 will also have a virtual link with Router2 with transit area as Area 1.

In case the link between PE1 and Router1 fails:-

============================================

One virtual link has to be created on Router1 with transit area as Area2 peering with PE2. The PE2 router will have a virtual link with transit area2 peering with Router1.

Keep the backup link on Router 1 & 2 in area 2.

This will work in your case for maintaing the redundany.

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ganpatspatil Thu, 03/01/2007 - 06:15

Hi,

Pls explain in details what actually u want to say.........

As per my understanding u r haveing backup link between CE's.if this is the case than u have to use Sham-link between PE's for perticular CE.

kevin.hu Thu, 03/01/2007 - 07:15

I can't use Sham Link because Sham Link only works if all areas are the same. Please see my diagram. If my link to PE-2 fails, what do I need to do in order to achieve redundancy through the backup link?

Thanks.

Correct Answer
kunalpurk Thu, 03/01/2007 - 23:08

See....in this case , you will have to configure 2 virtual links to maintain full recahability between the routers in case of any link failures.

In case the link between PE2 and Router2 fails:-

============================================

One virtual links has to be created in the router configured in Area 2 with Transit area as Area 1 peering with the PE1.PE1 will also have a virtual link with Router2 with transit area as Area 1.

In case the link between PE1 and Router1 fails:-

============================================

One virtual link has to be created on Router1 with transit area as Area2 peering with PE2. The PE2 router will have a virtual link with transit area2 peering with Router1.

Keep the backup link on Router 1 & 2 in area 2.

This will work in your case for maintaing the redundany.

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