Ask Dr. Intranet

FRAMINGHAM (04/10/2000) - I've heard of two new acronyms that I believe are protocols. Can you explain what MPLS and MPOA stand for and what they are designed to do?

MPLS stands for Multi-protocol Label Switching. According to RFC2702, Requirements for Traffic Engineering Over MPLS, "Multi-protocol Label Switching integrates a label swapping framework with network layer routing. The basic idea involves assigning short fixed-length labels to packets at the ingress to an MPLS cloud (based on the concept of forwarding equivalence classes).

Throughout the interior of the MPLS domain, the labels attached to packets are used to make forwarding decisions (usually without recourse to the original packet headers)."

MPOA stands for Multi-Protocol over ATM. The ATM Forum specification says MPOA's goal is efficient transfer of intersubnet unicast data in a LAN emulation environment. MPOA integrates LAN emulation and the Next Hop Routing Protocol to preserve the benefits of LAN emulation, and allows intersubnet, internetwork layer protocol communication over ATM with no routers in the data path.

Both protocols de-couple the forwarding of a packet from the contents of the packet's IP header, which is useful for features such as VPN support.

For more on multiprotocol switching, see Raj Jain's page at jain/refs/ipsw_ref. htm, the ATM Forum ( and the IETF (

Blass is a network architect at Sprint Paranet in Houston. He can be reached at

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