EoMPLS encapsulates Ethernet frames in MPLS packets and forwards them across the MPLS network. Each frame is transported as a single packet, and the PE routers connected to the backbone add and remove labels, as appropriate, for packet encapsulation:
- The ingress PE router receives an Ethernet frame and encapsulates the packet by removing the preamble, the Start Frame Delimiter (SFD), and the frame check sequence (FCS). The rest of the packet header is not changed.
- The ingress PE router adds a point-to-point virtual connection (VC) label and a label-switched path (LSP) tunnel label for normal MPLS routing through the MPLS backbone.
- The network core router uses the LSP tunnel label to move the packet through the MPLS backbone and does not distinguish Ethernet traffic from other types of packets in the MPLS backbone.
- At the other end of the MPLS backbone, the egress PE router receives the packet and de-encapsulates the packet by removing the LSP tunnel label, if present. The PE router also removes the VC label from the packet.
- The PE router updates the header, if necessary, and sends the packet out of the appropriate interface to the destination switch.
The MPLS backbone uses the tunnel labels to transport a packet between the PE routers. The egress PE router uses the VC label to select the outgoing interface for the Ethernet packet. Because EoMPLS tunnels are unidirectional, for bidirectional EoMPLS, you should configure one tunnel in each direction.
The point-to-point VC requires you to configure VC endpoints at the two PE routers. Only the PE routers at the ingress and egress points of the MPLS backbone know about the VCs dedicated to transporting Layer 2 traffic. Other routers do not have table entries for these VCs.
Restrictions for EoMPLS
- When configuring an EoMPLS pseudowire on the Cisco ASR 901 1 Router, you cannot configure an IP address on the same interface as the pseudowire.
- EoMPLS xconnect with VLAN range is not supported.
- EoMPLS xconnect port with double-tagged encapsulation is not supported.
- When port channel is configured on the MPLS core, the encapsulation ID should be equal to the bridge domain.
- To configure cross-connect with dot1ad encapsulation on an EVC, the interface should be a dot1ad NNI port. This means that a service instance with dot1q encapsulation cannot be configured on the port.
- Port-based cross-connect cannot be configured on the dot1ad NNI port interface.
- The encapsulation dot1ad command with cross-connect is not supported on the port channel.
- The dot1ad encapsulation with cross connect is not supported for double tag (QinQ).
- In case of encapsulation dot1ad over cross-connect, push operation at egress is not possible on cross-connect port in scenarios which requires pushing an additional dot1ad tag on the incoming dot1ad tag.
- The maximum number of cross-connect sessions supported on the Cisco ASR 901 Router is 1000. In case of pseudowire redundancy, a maximum of 500 sessions for primary and 500 sessions for backup pseudowire are supported.
- Default EFP under xconnect and untagged EFP under bridge domain on the same interface are not supported.
- Encapsulation is supported only on bridge domain and cross-connect.
- The rewrite command in the default EVC encapsulation is rejected.
- Default encapsulation with cross-connect is not supported on the port-channel interface.
- Untagged EFPs are supported only on the port with default encapsulation.
- Layer 3 routing is not supported. Layer 2 VPN is supported on the default encapsulation EFP.
- DSCP based classification for marking is not supported.