MPLS

In theory, MPLS forwarding might be marginally faster than IP forwarding (due to simpler label lookup), but I have never seen actual data from a vendor claiming significantly faster MPLS forwarding performance.

The term multi-protocol means this type of service uses any kind of protocol – it’s not restricted to any particular type of protocol – hence, multi-protocol.

MPLS Label Structure

• Label: label value, 20 bits.



• EXP: Experimental bits, Name is currently changed to Traffic class, 3 bits.



• S: bottom of stack, 1 bit.



• TTL: Time to live, 8 bits.

A couple of definitions are important before moving to MPLS operation:

• Downstream router: This is the router which advertises the prefix. In other words the router that is the next hop to a specific prefix is the downstream.



• Upstream router: This router receives the routing information from its downstream router.



• Label Edge Router (LER): Operates at the edge of the MPLS network (ingress/egress) and make forwarding decisions based on the IP header information of the packet.



• Label Switch router (LSR): the routers in the middle of the MPLS network which forwards MPLS packets based on label information.