[c-nsp] EoMPLS restrictions

[Peter Rathlev]

Hi Nasir,

On Wed, 2009-02-25 at 12:01 +0000, nasir.shaikh at bt.com wrote:
> Can someone shed some light on the following limitation of EoMPLS?
> Layer 2 connection restrictions:
> - You cannot have a direct Layer 2 connection between provider-edge
> routers with EoMPLS
> Why is this?

The only place I can find this sentence is in the 3750 Metro
documentation. I too cannot figure out what it means exactly, but I have
no experience with the 3750 Metro.

> I have a MAN running MPLS where my PE are directly connected. I need
> to do extend my datacenter LANs from location A to location B. I was
> thinking of using EoMPLS but this limitation is bothering me because I
> don't understand this limitation.
> Anyone care to explain?

I you want to transport incoming traffic via an EoMPLS VC from one PE to
another, there should be no problem with this even if they're directly
connected. As long as the direct connection is an MPLS link and you have
a working LSP you should be fine. We do this with 6500 Sup720s in many
places. (I assume the 3750 Metro works in the same way.)

> Topology as under:
> CE--(trunk)dot1q(tunnel)-->PE--MPLS--PE--tunnel(dot1q)trunk-->CE
>                                                |                     |
>                                          MPLS           MPLS
>                                                |                     |
> CE--(trunk)dot1q(tunnel)-->PE--MPLS--PE--tunnel(dot1q)trunk-->CE
> 
> The CE on the right hand side are under my control and there is
> another cascaded CE device behind which the data center resides. So I
> could convert the CE to a PE to resolve this.
> Any suggestions are welcome

The MPLS terminology I know of defines a "PE" a a box imposing or
deposing labels. An MPLS enabled box is thus either a "P" or a "PE".

In my eyes "standard" EoMPLS service is between xconnected outwards
facing (sub-)interfaces on PE1 and PE2 in a topology like this:

           ||
           || (802.1q trunk)
           ||
      +----------+
      |   CE 1   |
      +----------+
           ||
     --->  || (802.1q trunk)
           ||
      +----------+
      |   PE 1   |
      +----------+
           |
           | (MPLS LSP)
           |
      +----------+
      |   PE 2   |
      +----------+
           ||
     --->  || (802.1q trunk)
           ||
      +----------+
      |   CE 2   |
      +----------+
           ||
           || (802.1q trunk)
           ||

The EoMPLS connection would be where the arrows are. As I understand
your diagram this would be possible, maybe even trivial, to implement.

Regards,
Peter