MPLS Layer 3 VPN Explained

Hi @kumaracp10,

Many thanks for your excellent question. If you are referring to MPLS labels, this is primarily used as a method to quickly switch IP packets within the MPLS core. This is the most basic feature of MPLS so it is used in all MPLS networks even if there is no VPN overlay. The 1st MPLS tag exists only to enable MPLS forwarding plane operations.

**If we decide to operate a VPN over MPLS, a second MPLS tag is added** to allow PEs to know how to efficiently forward incoming packets.

In MPLS there are two basic rules that help us unpick the architecture:

  1. Separate the control plane from the forwarding plane:
    Control plane: routes being shared between CE<==any routing protocol==>PE and PE<==BGP==>PE)
    Forwarding plane: MPLS labels applied to real customer packets full of customer data, to forward them efficiently.

  2. Always remember, packets with routes go one way, packet with useful customer data go the other way. “We send routes in order to receive data”.

I hope that helps a little to clarify. Kind regards,
Jon.

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