Ethernet over MPLS (EoMPLS) is a tunneling mechanism that allows you to tunnel Layer 2 traffic through a Layer 3 MPLS network.
EoMPLS is also known as Layer 2 tunneling.
EoMPLS effectively facilitates Layer 2 extension over long distances. EoMPLS over GRE helps you to create the GRE tunnel
as hardware-based switched, and encapsulates EoMPLS frames within the GRE tunnel. The GRE connection is established between
the two core routers, and then the MPLS label switched path (LSP) is tunneled over.
GRE encapsulation is used to define a packet that has header information added to it prior to being forwarded. De-encapsulation
is the process of removing the additional header information when the packet reaches the destination tunnel endpoint.
When a packet is forwarded through a GRE tunnel, two new headers are added to the front of the packet and hence the context
of the new payload changes. After encapsulation, what was originally the data payload and separate IP header are now known
as the GRE payload. A GRE header is added to the packet to provide information on the protocol type and the recalculated checksum.
A new IP header is also added to the front of the GRE header. This IP header contains the destination IP address of the tunnel.
The GRE header is added to packets such as IP, Layer 2 VPN, and Layer 3 VPN before the header enters into the tunnel. All
routers along the path that receives the encapsulated packet use the new IP header to determine how the packet can reach the
In IP forwarding, on reaching the tunnel destination endpoint, the new IP header and the GRE header are removed from the
packet and the original IP header is used to forward the packet to the final destination.
The EoMPLS over GRE feature removes the new IP header and GRE header from the packet at the tunnel destination, and the MPLS
label is used to forward the packet to the appropriate Layer 2 attachment circuit or Layer 3 VRF.
The scenarios in the following sections describe the L2VPN and L3VPN over GRE deployment on provider edge (PE) or provider