OpenFlowMPLS MPLS Operations

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MPLS Operations

MPLS imposes the label switching paradigm to forwarding.
A MPLS path will have three types of nodes:

• Ingress (Tunnel Encapsulation)
• Transit (Label Switching)
• Egress (Tunnel Decapsulation)

The actions required at these nodes are:

• Push (Path Ingress)
• Swap (Transit)
• Pop (Path Egress)
• PHP (Penultimate Hop Popping, used to avoid Pop at the egress node)
• Swap & Push (Nested Path Ingress)
• Pop & Swap (Nested Path Egress)

Further functionality required at the nodes:

• Forward to the MPLS next hop
• TTL handling

Forwarding to the MPLS NHop:
After performing the action on the labeled packet, it is forwarded to the next node in the MPLS path. This is done by re-writing the destination MAC to the MAC address of the nexthop. Also the source MAC of the packet is changed to the source MAC of outgoing MPLS interface.

TTL Handling:
TTL handling requires a number of operations:

• Move the TTL from the IP header to the MPLS label at ingress node
• Decrement the label TTL at the transit and egress nodes
• Move the TTL from the label to the IP header at the egress node
• If the incoming label TTL is 1 at the transit or egress node then do not forward the packet. Instead punt it to the controller for further handling