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New Member

Tweak the routing over multiple site links with OSPF

Hi All,

I'm hoping an OSPF guru can help me fathom out an issue with getting OSPF to route in the directions I want.  Essentially the scenario is this:

- There are three sites all connected together via 1Gb VPLS

- SITE 1 and SITE 2 are also connected directly via a 1Gb LES

- Each site has two core switches with the VPLS connecting to Core 1

- For SITE 1 and SITE 2 the 1Gb LES connects to Core 2

- The core switches communicate via a routing VLAN

- OSPF is used to share routes between the 2 core switches but also between the cores in the other sites

- Area 0 is used

At the moment the problem we have is mainly between SITE 1 and SITE 2.  We want traffic between these two sites to use the LES and only use the VPLS if the LES fails.  However at the moment the VPLS is used out of Core 1 and the LES is used out of Core 2.  We would prefer everything to go just one way.

We also want to ensure that SITE 3, which just has VPLS, goes direct over the VPLS to each of the other two sites but has the ability to go via SITE 2 if SITE 1's VPLS fails and vice-versa.

I've tried using costing to change the routing but with limited success.  Is there something else I should be trying?

I hope I've been clear with this and really hope someone can help as my OSPF skills are pretty basic!

Craig

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New Member

Re: Tweak the routing over multiple site links with OSPF

I don't see why we can't set this up how you want.

If you currently configuring all routers (L3 switches) in Area 0, I would expect to see these adjacencies:

Point to Point: Site 1 Router 2 <-> S2R2;

Broadcast:     S1R1, S2R1, S3R1

Each site's routers should be giving OSPF their connected and local routes as Type 1 and Type 2 LSAs - we should not see any Type 3 LSAs as we are a single area.

Site 1 <-> Site 3 and Site 2 <-> Site 3 traffic should be direct over VPLS with only one route available.

Site 1 <-> Site 2 should have two paths, via R1 and R2.  These may or may not be equal cost depending on the configuration.

We should be able to traffic engineer using cost variables to prefer LES over VPLS for Site 1 <-> Site 2.

Can you pass over your current configuration and we can baseline and test this out in GNS3.

Regards, Ash.

2 REPLIES
New Member

Re: Tweak the routing over multiple site links with OSPF

I don't see why we can't set this up how you want.

If you currently configuring all routers (L3 switches) in Area 0, I would expect to see these adjacencies:

Point to Point: Site 1 Router 2 <-> S2R2;

Broadcast:     S1R1, S2R1, S3R1

Each site's routers should be giving OSPF their connected and local routes as Type 1 and Type 2 LSAs - we should not see any Type 3 LSAs as we are a single area.

Site 1 <-> Site 3 and Site 2 <-> Site 3 traffic should be direct over VPLS with only one route available.

Site 1 <-> Site 2 should have two paths, via R1 and R2.  These may or may not be equal cost depending on the configuration.

We should be able to traffic engineer using cost variables to prefer LES over VPLS for Site 1 <-> Site 2.

Can you pass over your current configuration and we can baseline and test this out in GNS3.

Regards, Ash.

New Member

Re: Tweak the routing over multiple site links with OSPF

Hi Ash,

I believe we've got the routing to behave as expected now.  I hadn't noticed that an OSPF cost of 100 was placed on the VLAN interface that connects the two cores at one of the sites together.  Traffic was therefore behaving incorrectly for all traffic relating to this subnet and all cascading devices.  All costs have been matched up now at all sites so I think we're set.  Thanks for offering your help.

Craig

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