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MPLS circuits integration in existing OSPF WAN

We're currently starting to implement MPLS in an existing hub-and-spoke OSPF environment with core area 0 routers connecting to various stub areas in each geographical location.

We own the CE router in each location. My question is the following:

Should we extend area 0 to each of these remote locations in Asia, Europe and Latin America? Or should we configure the MPLS circuit to be in the stub area?

One other alternative is to use a new area common for All MPLS connections only.

What would be the best pricatice and advantages in each case?

Please bear in mind that some locations are already configured as stub and currently running OSPF. The same locations will ultimately move away from Point-to-Point circuits to MPLS.

Thanks and regrads.



Re: MPLS circuits integration in existing OSPF WAN

Do you mean you will subscribe the MPLS service from a Telco and enable the OSPF on it. i.e. MPLS is not configured by you and you use OSPF over the MPLS ?

The OSPF area, you can follow OSPF design guide that it is recommended no more than 65 routers in a single area. If you only have a few sites, it is fine to use single area for simplification. If you have more routers and planning to increase in future, you may consider to segment it by different area. Or you want to control the routes between region, you can also implement areas in each region. e.g. 4 areas, area 0 = core, area x,y,x = three regions.

Please advise more information then we can provide more comments.

Check below for the OSPF design guide :

Hope this helps.

Community Member

Re: MPLS circuits integration in existing OSPF WAN

Thank you for you reply.

Yes, the telco is enabling OSPF on its PE and providing us with a public IP address to use on the CE side.

We currently have five areas as you've mentioned and we've followed the design guide: Area 0 for core, one area for Europe, one for Asia and one for Latin America, plus one the US (all are stub areas). Our core routers are both 7200's and 3662's and have between two or three areas defined on them. Most circuits are point-to-point DS3's, E1's and DS1's

Our Telco is recommending extending area 0 to all sites that are implementing MPLS (across 4 continents). We're reluctant to do that because of re-configuration factors and because these sites already have OSPF defined (stubby areas)and running pt-to-pt connections to the main data centers in the core.

Routes in OSPF show as E2 anyway, as no neighborhood is established between the different sites.

My question relates to whether I should group MPLS circuits under the same OSPF area (< 32 routers) or use the existing stubby areas as the geographic locations? Advantages and disadvantges of each.

Many thanks.



Re: MPLS circuits integration in existing OSPF WAN

Thanks for the detail information.

What I suggest if the current OSPF area design is working fine and fit your requirement. There is no reason to change it unless there is modification can enhance the design. Did the Telco tell the reason thy group to one ? Is there any policy or difficulty from them ?

What I expect you have area 0 configure at core router /site and also enabled other four areas at the core router /site too. And the remote routers only have the non-area 0 configuration. Right ?

If this is the case, I will recommend only extend the area 0 to the remote router when the MPLS connected interface, and the local or the sites behind this router will retain on the current area. i.e. move the role of ABR from core to the remote. The benefit of this design is the Telco will still find it is the same area in all sites but you still have the control on the different areas.

In fact, I will recommend to maintain the current design first then check is there any issue on management and performance side. If not, keep the current design. Otherwise, reconsider another design, e.g. single area 0.

What I think, the reason of single area is due to the topology change from hub-and-spoke to mesh design. Where MLPS / IPVPN is point-to-multiple point / mesh design, so use single area can allow all routers to talk to each other directly. However, your current routing policy may not be retained and require redesign. I believe it is not what you expect.

Therefore, if there is no policy or performance impact, maintain the current design is fine until there is a need.

Hope this helps.

Community Member

Re: MPLS circuits integration in existing OSPF WAN

Is the MPLS network replacing the existing point to Point circuit?

I would be very reluctant to extend area 0 across the providor network. Give the previous exchange I would lean toward selecting a new area for all MPLS sites. The MPLS router/routers at your core locations would be your ABRs(this would require reconfiguration, but would allow site to site routing, within the MPLS cloud. This design also assumes that the MPLS cloud is not your primary connection between Core sites.

Community Member

Re: MPLS circuits integration in existing OSPF WAN

Ultimately (probably within 2 yrs) it will; currently there is one existing site that will have both and two new sites that will only be on MPLS, plus one of the core sites.

I agree with you on not extending area 0 thru MPLS and am also leaning towards a common area for all MPLS interfaces.

What sort of reconfiguration do you think the ABR's would require?



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