Manual

Layer 2 Tunnel Protocol Version 3

Information About Layer 2 Tunnel Protocol Version 3

Cisco IOS Releases 12.0(29)S and 12.2(25)S

Protocol Demultiplexing for L2TPv3 Restrictions

• IPv6 protocol demultiplexing is supported only for Ethernet and terminated DLCI Frame Relay

interfaces.

• Frame Relay demultiplexing is supported for point-to-point or multipoint.

• FRF.12 end-to-end fragmentation is supported on the Cisco 7500 series routers only between the CE

and the PE routers.

• FRF.9 hardware payload compression is supported on the Cisco 7200 and Cisco 7500 series routers

only between the CE and the PE routers.

• FRF.9 software payload compression is supported on the Cisco 7500 series routers only between the

CE and the PE routers.

• FRF.9 process switched payload compression is not supported.

• IETF encapsulation must be used with FRF.9.

• FRF.16 is supported only between the CE and the PE routers.

L2TPv3 Control Message Hashing Restrictions

• L2TPv3 control connection authentication configured with the digest command requires

bidirectional configuration on the peer routers, and a shared secret must be configured on the

communicating nodes.

• See Table 4 for a compatibility matrix of all the L2TPv3 authentication methods available in

Cisco IOS Release 12.0(29)S.

Information About Layer 2 Tunnel Protocol Version 3

To configure the Layer 2 Tunnel Protocol Version 3 feature, you must understand the following concepts:

• Migration from UTI to L2TPv3, page 10

• L2TPv3 Operation, page 11

• Benefits of Using L2TPv3, page 12

• L2TPv3 Header Description, page 13

• L2TPv3 Features, page 14

• L2TPv3 and UTI Feature Comparison, page 18

• Supported L2TPv3 Payloads, page 19

Migration from UTI to L2TPv3

UTI is a Cisco proprietary protocol that offers a simple high-speed transparent Layer 2-to-Layer 2

service over an IP backbone. The UTI protocol lacks the signaling capability and standards support

necessary for large-scale commercial service. To begin to answer the need for a standard way to provide

large-scale VPN connectivity over an IP core network, limited migration from UTI to L2TPv3 was

introduced in Cisco IOS Release 12.0(21)S. The L2TPv3 feature in Cisco IOS Release 12.0(23)S

introduced a more robust version of L2TPv3 to replace UTI.