Chapter 10. Understanding L2TPv3
As mentioned in Chapter 3, "Layer 2 VPN Architectures," Layer 2 Tunnel Protocol Version 3 (L2TPv3) is an IP-based solution in the Cisco Unified VPN Suite that provides pseudowire emulation for a variety of Layer 2 protocols, including Ethernet, High-Level Data Link Control (HDLC), PPP, Frame Relay, and ATM. The base L2TPv3 protocol, which includes the control protocol and data encapsulation, is defined in the Layer 2 Tunnel Protocol Extensions (l2tpext) working group. At the time of this writing, the L2TPv3 base draft had not reached RFC status. Supplemental specifications that are particular to the data link protocols such as ATM are defined in separate drafts. This chapter examines the base L2TPv3 protocol by first reviewing the history of its development from its prestandard beginnings. This exploration into the protocol's evolution is then followed by an examination of L2TPv3's data encapsulation and control channel signaling. |