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l3 mpls network with out P router, all PE to PE plus daisy chainging

Guys, is it possible to run a core l3 MPLS network over 7600s and 3800s with out any P routers? The reason i aak is because of the particular situation where we will have to daisy chain PE routers due to lack of fiber.

any thoughts?

4 REPLIES

Re: l3 mpls network with out P router, all PE to PE plus daisy c

Hello,

Every Cisco PE will also be a P router for other PEs. The reason is, that all a P does is label switching and this is also part of a PE function.

So there is no problem to omit P routers completely. In fact I was involved with an enterprise customer, who implemented exactly this - only PE routers and no specific P routers. Works like a charm.

Hope this helps! Please rate all posts.

Regards, Martin

Bronze

Re: l3 mpls network with out P router, all PE to PE plus daisy c

As martin says absolutley limited problems with this it will work a charm UNTIL yo urun into scaling issues. You are daisy chaining all the PEs which would also suggest to me that you are daisy chaining your RRs. In an mpls network the RR's have enough state to handle to keep them busy enough without also having to deal with passing labels about the network. Also you will have any cisco account team breaking down your door putting the fear of god into you for not having at least 2 P routers ;-). So yes you can indeed run it like you say but the lifetime of your network will be very limited indeed. If your not an SP then dont be concerned - unless you are an enterprise with 10000000s routes then id start to worry. Oh they (cisco) also state that PEs also have enough to do in their life without passing labelled packets about the place. sit and think about what your poor PE is having to do daily it could be 100 vrfs routing tables, which in turn means layer 3 lookups to find out where the packet has to go, qos, multicast, bgp, ospf, rip, eigrp, your own internal IGP, TE tunnels, RSVP - this poor router has enough to do without also adding transit traffic. ;-)

Re: l3 mpls network with out P router, all PE to PE plus daisy c

Hello,

what Rob wrote is for sure true. Make sure the box you implement handles the traffic and features now and in the forseeable future.

On the other hand f.e. a Cat6500 with Sup720 will be able to forward 50 Gig/s of traffic and handle the internet BGP table at the same time. Thus even for most SPs such a box in the MPLS environment would be sufficient even when combining RR and PE and P functionality in one machine.

I wouldn´t bet a 3640 could do the same ... ;-)

So choose your hardware carefuly based on the requirements (cost, cost, and ... anything else?) and you should be fine.

Last thought: do not forget about operational flexibility. I mean you could take all the features IOS offers and turn them on in one box. But hey do you find anyone understanding to troubleshoot this? What if you need to upgrade something (hardware, or in the most unlikely case of an IOS bug ...) can you turn it off?

Hope this helps! Please rate all posts.

Regards, Martin

New Member

Re: l3 mpls network with out P router, all PE to PE plus daisy c

Thanks for the input. My route reflectors will not be daisy chained, they will be in a core. I will only have to daisy chain 4 or 5 sections with a mac of 4-5 hops each. thank you very much for everyones input

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