MPLS without Ps

Unanswered Question
Mar 24th, 2007

Dear Sir,

i want to know if i can build a mpls backbone without P Routers where all the backbone routers (for excample if i have 3 core 7600 routers connected together and configured as PEs where the VRFs is configured on it)


I have this problem too.
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Harold Ritter Sat, 03/24/2007 - 17:33

Yes, it is perfectly acceptable to build an MPLS core without having P routers.

Hope this helps,

exchange1 Mon, 03/26/2007 - 06:45

If i build MPLS without P routers what will happen to the IGP, do I still run IGP between the PEs? or I'll be limited to I-BGP and MP-BGP?

Harold Ritter Mon, 03/26/2007 - 06:56

You still need to run an IGP even though all of the PEs are directly connected. This will provide IP connectivity to the loopback interface IP address between all PEs.

Hope this helps,

Harold Ritter Mon, 03/26/2007 - 09:28

I forgot to mention the reason why it is important to have loopback interface IP address connectivity between the PE routers. LDP generally uses the loopback interface IP address to establish its TCP connection from one neighbor router to another. Without this connectivity, LDP won't be operational.

Hope this helps,

royalblues Wed, 03/28/2007 - 05:46


We are also planning to build our own MPLS backbone

What is the criteria to decide whether to use P routers in the cloud.


Harold Ritter Wed, 03/28/2007 - 06:04


I would say that it all depends on the size of your network and how large it has to scale. If you only have a handful of PEs and you are not planning on growing that number then it is fine to have only PE routers.

It is worth noting that these PE routers may functionally become P routers themselves if they are used to transit traffic between two other PEs.

Most MPLS networks I have dealt with in the last couple of years were large enough to justify the use of dedicated P routers (no customer aggregation).

Hope this helps,

IVAN PEPELNJAK Wed, 03/28/2007 - 09:58

Running PE-only MPLS network is perfectly OK. It's easiest (and most scalable) if you configure loopback interfaces, run IGP on all global interfaces in inter-PE VPNv4 iBGP sessions between loopbacks. This also gives you ability to insert P-routers when needed.

While there are potential alternate designs running iBGP directly over PE-PE links and even avoiding running IGP at all, I would strongly discourage that, as it will only bring you headaches in the future.

defash Fri, 06/08/2007 - 04:03

I have three POPs with one of the POP having four PE (7609) routers and one P (12410) router, while the remaining two POPs has one PE each. We are looking at doing CSC with another MPLS provider whose route covers different region. We are also looking at Internet peering with Tier-1 content providers. Is this design acceptable for a provider looking at providing carrier grade MPLS services and if no, whatoptions are available.

swaroop.potdar Fri, 06/08/2007 - 05:32

What a customer would expect from a carrier grade service is optimal uptime and strict adherence to SLA's. Thats all.

You may want to relook at redundancy of each pop in terms of link level and device level, and also may want to think of implementing FRR between your pops. If these points are taken care of for now for the 3 pops you should be able to provide good service.

As far as you doing CSC and content peering is concerned, its not limited by you having only 3 pops and neither does it affect in any way in providing carrier grade service.



soin-kamal Wed, 06/13/2007 - 05:25

See VRF is always on the provider side...Customer site never know about the VRF' create VRF on PE router...

What are you using..ISC ???/ then it will automaticaaly provides you with RT and RD...

soin-kamal Wed, 06/13/2007 - 05:27

VRF will be created on the router pointing towards the customer route....


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