Why not extend BGP to CE routers?

[Venison Mogambi]

I'm working on an MPLS/VRF lab scenario and the lab has me running OSPF between the CE and PE routers, then redistributing into MP-BGP so that the customer routes can be carried across the MPLS core, then on the far end of the MPLS cloud at the PE-CE link redistributing again, from MP-BGP back into OSFP. I believe this is kind of a standard practice with MPLS SP networks; to run an IGP with the customer and then run MP-BGP across the MPLS core. But why not just extend MP-BGP and the VRF down to the CE router? I feel like redistribution often causes issues and, at least in my little lab scenario, it seems unnecessarily complicated to redistribute once at the ingress to the MPLS cloud (OSPF-to-BGP), then redistribute again at the egress (BGP-to-OSPF). It seems easy enough to just configure the CE as a BGP peer, define the VRFs right there on the CE router and advertise the customer prefixes directly into your MP-BGP.

Generally speaking, what are the reasons that SPs would avoid this and instead opt to use IGP with the customer?

[Nagendra Kumar Nainar]

Hi Vension,

BGP can be used as PE-CE protocol. AFAIk, there are many MPLS providers with PE-CE as BGP. Some customers might be running OSPF as IGP already and they just need to extend one more neiighbor towards PE router. While otehr customers might be multihomed and need more control over how a traffic comes in and goes out. In these scenarios, BGP helps with more control.

So it depends on the customer needs. 

HTH,

Nagendra

[Masoud Pourshabanian]

Hello,

It is possible. Then a CE router would be performing like a PE. You can connect a computer to a PE router and communicate, but what is the drawback? You need to keep customers side as simple as possible.  Customer does not have any Idea about VRF and MPLS labels. What if customer router does not support MPLS? What if a customer just has a modem and a computer? What if customer does not have any knowledge about VRF and MPLS?

CE just need a IP and a default route to connect to a MPLS network in a simple network.

Masoud

[Jon Marshall]

Just to add that from my experience in the UK using BGP is a common occurrence.

The advantage as you point out is that the SP does not need to setup redistribution because it happens automatically.

However it is not standard practice, as far as I know,  to extend the VRFs to the CEs because ,as Masoud points out, you are then expecting customers to understand MPLS labels and VRFs etc and you want to keep it as simple as possible for them.

So BGP between the CE and PE definitely but just a normal BGP session exchanging IP routes.

That doesn't mean you can't use an IGP if the SP offers it and it fits with your network design.

Like I say that is my experience but it has been a while since I did this so maybe things have changed and I can't say what is standard practice in other countries although we do see a fair few posts on these forums where BGP is being used by the customer.

Jon