Hi,
Not really my speciality but I do configure some such connections at work at my local ISP. I dont specifically handle the core network but have tried to learn some so I can handle the whole customer environment instead of just limiting myself to Firewall and VPN.
In our environment the most common setup is extending a L2 segment between 2 locations of our customer which are both connected to our core network. In this setup we basically configure an EoMPLS (Ethernet over MPLS to my understanding) which connect the 2 sites at L2. This is handled in the ISP core and the customer site might be as simple as only having a DSL modem or L2/L3 switch.
If your sites are connected to 2 different ISPs then it probably becomes more complicated.
We do have setups like this also, but in these cases the other ISP provides the L2 connectivity to from one customer site to the link between our Core networks. We then handle the L2 connection from that point all the way to the other site in our core network.
There is also one very commonly quoted setup of which I have no expirience of.
This seems to be one document/post about it
http://packetpushers.net/extending-layer-2-across-layer-3-with-l2tpv3-pseudo-wires/
- Jouni
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