How L2VPN Traffic flows inside mpls n/w

[AbuRafay63]

Hi support,

I need to know any supportive material to know , How L2VPN Traffic flows inside mpls n/w. Suppose one customer is attached to PE1, its other branch attached to PE2. Routes came to PE1, how they will travel to PE2 , to reach that branch connected to PE2?? Briefly explain here as well for VPLS too. Thanks

BR:Kamran

[Victor Acevedo]

Hello AbuRafay,

With L2VPN services, the customer does not share any routes with your MPLS network. Their traffic will be completely transparent to the MPLS provider. What will happen is the two PE's will establish a Pseudowire (PW) "tunnel" and allocated a specific label for this customer.

When the customer sends traffic to your network, it will hit an interface with this PW tunnel and hence will be tunneled across to the remote PE using the negotiated label. Hence, the packet received from the customer is never routed, nor re-written and delivered to the remote customer site as it arrived. 

VPLS functions in the same way, except with VPLS, it is point-to-multipoint or multipoint-to-multipoint technology in which you can now send to multiple PE's. Since we now have more than 1 neighbor, your PE boxes will participate in MAC learning for your customers traffic.

More information regarding EoMPLS and VPLS:

EoMPLS

VPLS

Thx,

Victor Hugo Acevedo

[sabkar]

L2VPN the PW Concept :-

• A Pseudowire is defined as a VC connecting two Attachment VCs. In [MARTINI-SIG], a Pseudowire consists of two VC LSPs (Label Switched Paths), one in each direction. Each endpoint initiates the setup of the LSP that carries packets in the "incoming" direction (note that the Pseudowire itself is bi-directional).
• Pseudowires are carried within one or more MPLS or IP tunnel across the network. For MPLS networks, these Tunnels are also referred to as LSP tunnels. For a L2 transport service, an end-to-end virtual circuit between two CEs can be defined as an ordered triple <Attachment VC, Pseudowire, Attachment VC>.

L2VPN is a end to end layer 2 connection and no routing is involved. 

How the packet traverse through L2VPN :-

PACKET :- ETHERNET PDU || CW  | VC LABEL ||TUNNEL LABEL || LOCAL HEADER ||

Transport Header :- Tunnel Label ( MPLS LABEL 2BYTES ) = Established through the LDP link or RSVP. 

Tunnel Label :- VC Label ( MPLS label ) 4 Bytes :- Signalled through the Extended LDP session established between PE pairs ( Martini ; PWE3 based draft)

Control Word :- Control Word (Opt) + Customer payload 

So in the forwarding plane Customer payload will encapsulated inside the VC label and tunnelled inside the PW to reach towards the egress PE.