Current Meeting Report

2.2.9 Layer Two Tunneling Protocol Extensions (l2tpext)

NOTE: This charter is a snapshot of the 53rd IETF Meeting in Minneapolis, MN USA. It may now be out-of-date. Last Modified: 07-Mar-02
W. Mark Townsley <>
Internet Area Director(s):
Thomas Narten <>
Erik Nordmark <>
Internet Area Advisor:
Thomas Narten <>
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Description of Working Group:
This group is responsible for extensions to the Layer 2 Tunneling Protocol. Examples of L2TP "extensions" include any changes to the L2TP encapsulation, control messages, or new AVPs sent in IETF standard control messages.

I. L2TP Background:

L2TP (RFC2661) provides a means for tunneling PPP over IP. Because PPP can effectivly carry any traffic (e.g., IP (RFC 1332), IPX (RFC 1552), etc.) it can effectively be used to tunnel arbitrary protocols over IP. L2TP provides:

- An extensible control protocol for dynamic setup, maintenance, and teardown of multiple layer 2 tunnels between two logical endpoints.

- An encapsulation method for tunneling PPP frames between each endpoint. This includes multiplexing of multiple, discrete, PPP streams between each endpoint.

L2TP looks (in most ways) like just another point-to-point link to PPP and thereby take advantage of the work done for any protocol over a traditional PPP WAN link. It should be noted, however, that the ability to dynamically establish a PPP connection between any two IP connected endpoints brings new applications and challenges of scale to existing PPP implementations and protocol definitions that must be considered.

As high-speed broadband access to the home replaces traditional dialup infrastructure, L2TP has been utilized as one standard method for aggregation and delivery of PPP connections over packet networks. Thus, rather than a relatively small scale or low speed circuit-switched connection such as an analog modem or ISDN connection at the L2TP Access Concentrator (LAC), we see PPP being received over ATM PVCs which are generally higher speed and "always-on" vs. temporally connected. Further, there are non-IETF standard PPP tunneling protocols that have been developed and deployed, including PPPoE (RFC 2516) and the 3GPP2 Wireless GPRS Tunneling Protocol Standard ( that interface with L2TP at various points in the network. While it is unfortunate that there is more than one standard method for tunneling PPP defined, each of these have their own installed bases and specific application-driven nuances. Proper integration with these various tunneling methods as they "hand-off" to the L2TP portion of the network must be ensured.

II. L2TP Interaction with PWE3 for Pseudo-Wire Transport:

In addition to tunneling PPP, L2TPEXT will develop protocol extensions necessary for the tunneling of specific "pseudo-wires" as defined in the PWE3 WG. Specific milestone identification for this activity is currently subject to ongoing work and results from PWE3.

III. WG Activities

The Working Group is currently focussed on the following activities:

- RFC2661 bundles data transport, protocol signaling, and PPP emulation methods into a single document. This working group will separate RFC2661 into stand-alone documents for greater modularity. This will consist of a base L2TP document defining common tunneling constructs and encapsulation, and a PPP document defining the use of these constructs for tunneling of PPP sessions as defined in RFC2661. Documents for tunneling of pseudo-wires defined in PWE3 will be forthcoming as well.

As RFC2661 is rewritten to separate the tunnel setup and maintenance sections for support of new applications and increased modularity, some modifications to the base protocol may be necessary. This includes addition of a Pseudo Wire AVP to identify the pseudo wire being carried (with PPP identified as 0). In all cases, these will follow the extensible models offered in the L2TP base protocol design, with as much attention to backwards compatibility as possible given the new requirements.

In addition to its broader scope, L2TPEXT has ongoing work to complete from its inception as a tunneling protocol for PPP only. While RFC2661 will ultimately be made obsolete by a new L2TP base specification and companion PPP over L2TP specification, documents based on RFC2661 which do not require this new degree of modularity will still be published in the near term. These include:

- Identification of specific parameters and modes of IPsec in order to aid interoperability when IPsec is used to secure L2TP traffic.

- An L2TP MIB for network management.

- An L2TP Differentiated Services Extension to negotiate DSCP parameters to be set for packets associated with a given L2TP tunnel, sessions within a tunnel, or L2TP control traffic which may need differentiated QoS settings.

- Extensions to L2TP for additional or more robust control information for informational or operational purposes as deemed necessary based on operational experience. These include better transfer of L2TP PPP LCP Information between tunnel endpoints when such state needs to be shared, PPP Disconnect codes within L2TP control messages for better debugging, and L2TP session information for enhanced logging, billing, and error reporting.

- Standard methods for operation over such packet networks such as Frame Relay and AAL5.

- L2TP defines a base encapsulation for operation in typical environments for tunneling PPP at the time RFC2661 was being developed. In cases where bandwidth cost is at a premium, the size of the L2TP header becomes more significant. L2TP will define a compressed version of the L2TP header for these environments that takes advantage of the L2TP control plane to establish operational parameters allowing removal of information from individual packets.

Goals and Milestones:
Done   Submit L2TP over Frame Relay to IESG for consideration as a Proposed Standard
Done   Submit L2TP Security to IESG for consideration as a Proposed Standard
Jul 01   Submit L2TP PPP Disconnect Information to IESG for consideration as a Proposed Standard
Jul 01   Submit L2TP ATM extensions to IESG for consideration as a Proposed Standard
Jul 01   Submit L2TP MIB to IESG for consideration as a Proposed Standard
Jul 01   Submit L2TP Link Information to IESG for consideration as a Proposed Standard
Jul 01   Submit L2TP Session Info to IESG for consideration as a Proposed Standard
Aug 01   Submit L2TP Header Compression to IESG for consideration as a Proposed Standard
Aug 01   Submit L2TP Differentiated Services to IESG for consideration as a Proposed Standard
Aug 01   Submit L2TP over AAL5 to IESG for consideration as a Proposed Standard
Aug 01   Submit initial Internet-Draft of L2TP Base Specification
Aug 01   Submit initial Internet-Draft of PPP over L2TP
Request For Comments:
RFC3070PSLayer Two Tunneling Protocol (L2TP) over Frame Relay
RFC3145PSL2TP Disconnect Cause Information
RFC3193PSSecuring L2TP using IPSEC

Current Meeting Report

Notes taken by Stewart Bryant and Mike Horn, consolidated by Mark Townsley.

Intro - no comments from floor

plan to issue last call

Ron da Silva
L2TP Active Discovery
Few changes
Editorial update then request last call
No response from floor

M. Townsley - L2TP Extension for Frame Relay PW

Reviewed initial draft v00, requested feedback on the mailing list.

Comments: Discussions focused on fragmentation issues

Andy Malis - use FRF-12 in FR endpoint

George Wilkie - Fragmantation - best to do it on end systems, but need to be configured

Andy - use end-end frag on CE rather than UNI-NNI

Mark Townsley
L2TPv3 update
A number of clarifications made
Request publish update to sister PPP doc and move to last call shortly after this meeting

Mitsuru Higashiyama -
Ethernet over BCP over L2TP vs Ethernet over PWE3
PWE3 WG does not cover LAN to LAN compulsary tunnel
LAN to LAN voluntary tunnel competes with PWE3
Asked for opinion on whether he should keep comp & vol and let vol & Ethernet over PWE3 co-exist.

Comments: Discussion on whether there is enough WG interest to continue working on this draft unknown - The draft is potentially interesting for the DSL and ISDN use cases

Comment has use for DSL and ISL apps, needs discussion on list

Tmima Koren

Thomas Narten: Alloc of IP protocol number a problem. IESG will push back strongly in general, and because one already issued for L2TP.

Mark: Could use L2TPv3 at cost of extra 4 bytes, otherwise identify PID for session in setup negotiation. This is NAT unfriendly.

Thomas: Discomfort at neg PIDs on fly - firewall issue will restrict use. Existing protocols do not do this - doubts

Mark: use l2tpv3 would be a great approach but need input if this will put intended apps over the edge

Tmima - not a lot of difference but extra overhead a problem of competing against other technologies (ATM I think). Can we negotiate away L2TP session id

Mark: Yes, but could not support any demux

Stewart/Mark that means that HC must use UDP control channel because loose sesson ID.

Will ask Andy to spin new version with these comments.


None received.