The Layer 2 Tunneling Protocol (L2TP) is a standard protocol for tunneling L2 traffic over an IP network. Its ability to carry almost any L2 data format over IP or other L3 networks makes it particularly useful. But L2TP remains little-known outside of certain niches, perhaps because early versions of the specification were limited to carrying PPP -- a limitation that is now removed. It is desirable to tunnel L2 traffic over routed L3 networks because L2 networks are generally more transparent, easier to configure and easier to manage than L3 networks. These are desirable properties for a range of applications. In data centers, a flat network is essential for promoting virtual machine (VM) mobility between physical hosts. In companies with multiple premises, the sharing of infrastructure and resources between remote offices can be simplified by L2 tunneling. The L2TP protocol itself is an open standard defined by the IETF. This article concentrates on the latest Version 3 of the specification, which describes tunneling multiple L2 protocols over various types of packet-switched networks (PSN). The standard discusses tunneling over IP, UDP, Frame Relay and ATM PSNs.
Read the article over at Network World over here.