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I'm somewhat familiar with OSPF, having worked in an environment where it was used as the interior routing protocol. I'm unfamiliar with BFP but I'm working a project where BGP may be required. I understand that BGP has been modified to permit it to work with MPLS. Is the same true of OSPF?

Second question. It seems, from what I read, that BGP can be run as an interior routing protocol if one so desires. I also believe that BGP permits you to filter the routes that are advertised. Is anyone running BGP as an interior and exterior protocol and what, if any, are the advantages to running BGP in the interior as opposed to running OSPF or even EIGRP?


Re: OSPF vs. BGP and MPLS

I'm not sure why you would want to run BGP internally. It is far more complex than OSPF, and would probably require more overhead in terms of administration and configuration. As the name implies, it's really for Border Gateways. Use OSPF or EIGRP internally...that's what they were designed for.


(as far as the MPLS goes, I don't know how or why you would use it internally either...the best use for it I can think of is fully meshing a VPN based WAN)

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Re: OSPF vs. BGP and MPLS

MPLS can use BGP and ISIS routes to determind the best path using special extensions. I'm not sure if MPLS will use OSPF routes to include in the Label Switch Path (LSP), which are MPLS paths. MPLS can only be use for internal routing only, which means that you can not use it to provide routing outside your AS. And yes, you can run BGP as an internal protocal, its called iBGP. But it is best to use with other internal protocols such as ISIS and OSPF.

I hope this answer your questions.

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Re: OSPF vs. BGP and MPLS

If you are running BGP as an internal routing protocol (call it Internal BGP) you have to run an IGP like OSPF as well.

IBGP is required for e.g. ISPs which offer transit services. In this networks BGP is responsible for the external routes (there might be many of them) and an IGP is responsible for the internal routes.

Configuring IBGP might become a little complex, because a full mesh of IBPG connections is required. Therefore, ISPs are using Route Reflectors and AS Confederations. But this is another story ...



Re: OSPF vs. BGP and MPLS

Don't run bgp as an igp. It's not designed to do this. It's slow compared to real igp's, and the metrics aren't cut out for optimum routing, etc. Use a real igp for igp work, and bgp for egp work.



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Re: OSPF vs. BGP and MPLS


OSPF was modified to support MPLS-TE features.

You don't have to run OSPF or IS-IS on your network if you want to run MPLS on it. You can run any routing protocol (RIP, EIGRP, etc)... because what MPLS uses as the source for assigning labels is the information in the routing table, therefore it uses any routing source. Outer Labels are distributed via LDP.

If you are not running MPLS-VPNs on your network you don't need BGP.

On the other way it is a good idea to run MPLS between eBGP peers, because it avoids the BGP mesh scalability problems. The internal routers (those that don't run BGP) don't need to know the full internet routing table, they just need to know how to reach the eBGP routers, because all the traffic between them is label switched.

You should use OSPF or IS-IS because they are non-proprietary routing protocols, they converge quickly, they scale well and they support MPLS-TE, because both are link-state protocols and have a "global" view of the network.

Don't use (i)BGP as your IGP.

Hope this helps.


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