MPLS backbone without "P" routers

Unanswered Question
May 19th, 2010

Hello,

is there any drawbacks in MPLS backbone without "P" routers?

It means that a number of PE routers are interconnected directly with each other in some kind of ring topology.

As PEs we'd like to use one of Cisco's Switch with fully supported MPLS.

In which case the using of P routers would be necessary?

thank you for the replays,

Konstantin

I have this problem too.
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Giuseppe Larosa Wed, 05/19/2010 - 03:08

Hello Konstantin,

this is possible but:

>> with each other in some kind of ring topology.

this would rely on some L2 technology to handle the ring and even rapid STP would require tuning of the max-age timer in order to avoid to have STP BPDUs aged out.

if the number of devices involved is more then 8 I would deploy two or four core devices in order to contain the number of devices in a single ring.

Most deployments use point-to-point routed links to avoid to deal with L2 protocols and in this case the P nodes are a necessity.

Hope to help

Giuseppe

Konstantin Dunaev Wed, 05/19/2010 - 03:25

Hi Giuseppe,

thank you for the answer!

I already thought about L2 problem  and what I meant is to interconnect PE as via L3. In this case PE should speak with each other only L3: IGP and BGP and they should exchage the Lables for VPN and TE services. that is why we'd like to user MPLS "L4 switch"

The problem with "P" routers in our case is following, we have, let say, 6 big sites which are interconnected in ring topology and a number of satelate sites which are somehow connected to those "hub" sites. But we can't place in all those 6 site the additional HW (ther are some cost, place and "security" factors). We have only 3 site where we could place "P" routers, but those 3 sites are not directly connected.

Giuseppe Larosa Wed, 05/19/2010 - 04:33

Hello Konstantin,

a node can act as PE node for certain LSPs and as a P node for other ones no problem in this.

verify that all devices you want to use support MPLS, and a bigger MTU (each MPLS label requires 4 bytes)

Hope to help

Giuseppe

Konstantin Dunaev Wed, 05/19/2010 - 08:23

Thank you for the answer!

regarding HW you're right, we should check it out.

From the begining we  planed to use c7200 as PE router together with c3560 to aggregate to links on it. I think c7200 (NPE-G2) would be quite good in this role.

But then we met with Cisco consultant and he said that in near future will come a new Metro switch like ME3600 or something , with full MPLS features and it could replace c7200+c3560 and fit there very well .

But... as usual switches have quite limited space for  IPv4/Ipv6 route table and if some end-users would like to get the Full-BGP table, I don't think that those ME3600 switches can handle it.

What do you thing about?

Giuseppe Larosa Thu, 05/20/2010 - 00:39

Hello Konstantin,

>> But... as usual switches have quite limited space for  IPv4/Ipv6 route table and if some end-users would like to get the Full-BGP table, I don't think that those ME3600 switches can handle it.

I agree on this.

On the forwarding plane a C7200 NPE-G2 can be weak (you cannot expect to support 2 GE ports on it !), on the signalling plane it is strong enough to support full BGP table.

more expensive devices that could be considered include ASR 1000 series or C7600 with sup7203BXL.

the XL series has resources to handle a full BGP table and provides you very high forwarding capacity, you could consider a 7604 chassis or 7606

Hope to help

Giuseppe

Konstantin Dunaev Fri, 05/21/2010 - 00:05

Hello Giuseppe,

we're planning to stay at a sub-gigabit speed for a while, that is why we planed to put NPE-2G at forwarding plane as well. When we see that the  performance on some sites reachs a limit then we can replace them with a ASR1000 and use NPE-G2 as BGP router-reflectors for example.

Another possibility is to put c7200 as P router at the core, and use ME3600 (those new switches) as PE router, and for the customer which needs full bgp just give the multihop eBGP session to the Internet gateway router.

ramprasadd Fri, 05/21/2010 - 05:20

Hi,

my 2 cents here,

You need to select the platform based on services you are going to implement. If you are looking for MPLS-L3VPN and L2 VPN's(Sub-if based and port based)  C-7200 is good enough.

If you are looking for  VPLS services , L2VPN(Vlan based) and more flexible services 7600 (for this you need to have SIP cards) is good.

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