Thursday, February 26, 2009

L2VPN Over Metro Ethernet

In my previous post of, I described the modes of L2VPN and its provisioning. In this post I am going to elaborate how to deploy point to point L2VPN over Metro Ethernet rings with Q-in-Q tagging. The deployment is very lucid and trouble-free. As per the diagram customer is terminated on ME switch with Q-in-Q functionality. The focal advantage of using Q-in-Q in Metro Ethernet circuits to make customer frames unique within L2 domain and preserves the customer vlans. The flow is given below:-
CPE will forward the frames to PE switch with vlan tagging, after receiving the frames PE switch will encapsulate a more vlan tag on the existing vlan tag (It is like label with in label of layer 3 vpn). There after a sub interface is created on router physical interface by taking the same vlan as sub interface and xconnect is created over Ethernet domain by taking remote PE loopback as destination. When the frame is received by remote PE it will tag the frame again by preserving the existing customer vlan and forward to the Metro Domain. Where ever the packet will get out form the access port the upper tag of service provider domain will be removed and customer will able to get the valn tag which was being originated.
Why this type connectivity is being asked by service provider? Really awesome question, every service provider don't want to loose the confidentiality of its esteemed customers and used to promise their customers that they are Omni. Whenever customer demands the circuit at some remote locations and SP is not feasible on that location at that time layer 2 vpn services comes mostly in picture. One SP asks the another SP to provide the layer 2 circuit which looks like to customer that the whole backbone is being used by their service provider.
Monitoring of L2 circuits are not possible.


shivlu jain

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