[j-nsp] MPLSoMPLS - horrible?

[Alexandre Snarskii]

On Thu, Sep 30, 2010 at 05:52:56PM +1000, Dale Shaw wrote:
> Hi all,
> 
> I'm pondering my first production use of MPLS and I'm looking for some
> free advice.
> 
> I'm looking at building a new 'enterprise' network - an extranet of
> sorts - *on top of* a NSP's L3VPN service. It's all Ethernet. I'd like
> to be able to build my own pseudowires and create my own L3VPNs on top
> of the NSP's platform and without their involvement. In effect, my CE
> routers (from the NSP's perspective) become PE routers to *my*
> customers (3rd parties, e.g. business partners and suppliers).

It's called CsC - Carrier Supporting Carrier, and this technique is
known for years. 
 
> I suppose this means doing MPLSoMPLS, and actually depending on the
> upper layers in the protocol stack, it could end up looking pretty
> scary if you looked at what was being shifted around in the NSP's core
> :-)  (over and above MPLS, I'm thinking about how the stack looks when
> further encapsulation, such as IPSec, is used.)
> 
> So, noting the protocol stack size and potential MTU issues, is anyone
> doing this? How are you distributing labels?

Right question would be 'How do you exchange labels with your NSP?'.
Because if there are no such exchange your NSP will not know what to 
do with MPLS packet entering his network and will just drop it at 
ingress. 
 
> Is it too horrible to even contemplate?

It's hardly possible without setting CsC with your NSP. 

With L3VPN all you have is IP[v6] connectivity between your CE routers,
so the only way to run MPLS without NSP support is to run GRE tunnels
between your CE's and then run MPLS over these GRE tunnels. And, yes,
it is horrible: ethernet frame passing your pseudowire will become
ethernet over MPLS over GRE over IP over MPLS over ethernet with terrific 
overhead and lots of MTU issues :) 

> I'd be looking at using J and/or SRX as the "CE-pseudo-PE" devices.
> 
> Any pointers would be appreciated. I've only just embarked on this
> little adventure and I'm still relative new to Juniper platforms.
> 
> Cheers,
> Dale
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-- 
In theory, there is no difference between theory and practice. 
But, in practice, there is.