Nortel Networks Multi-link Multi-node PPP Bundle Discovery Protocol
RFC 2701

Document Type RFC - Informational (September 1999; No errata)
Author Gary Malkin 
Last updated 2013-03-02
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Network Working Group                                         G. Malkin
Request for Comments: 2701                              Nortel Networks
Category: Informational                                  September 1999

                            Nortel Networks
          Multi-link Multi-node PPP Bundle Discovery Protocol

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.


   This document specifies a standard way for Multi-link PPP to operate
   across multiple nodes.  Both the mechanism by which the Bundle Head
   is discovered and the PPP fragment encapsulation are specified.


   I would like to thank Joe Frazier for filling in some of the details
   and reviewing this document.

1.  Introduction

   Multi-link PPP [MP] allows a dial-in user to open multiple PPP
   connections to a given host.  In general, this is done on an on-
   demand basis.  That is, a secondary link, or multiple secondary
   links, are established when the data load on the primary link, and
   any previously established secondary links, nears capacity.  As the
   load decreases, the secondary link(s) may be disconnected.

   Many dial-in hosts which support multi-link PPP dial the same phone
   number for all links.  This implies that there exists a rotary at the
   Point Of Presence (POP) which routes incoming calls to a bank of
   modems.  These may be physically independent modems connected to
   Remote Access Server (RAS) and a rotary of analog phone lines, or a
   RAS with internal modems connected to analog lines or a T1/E1 or
   T3/E3 channel.  In any case, a given RAS can only handle just so many
   simultaneous connections.  A typical POP may need to support hundreds
   of connections, but no RAS today can handle that many.  This creates
   a problem when a user's primary PPP connection is established to one

Malkin                       Informational                      [Page 1]
RFC 2701                          MMP                     September 1999

   RAS in a POP and a secondary connection is established to another.
   This may occur because the first RAS has no available modems, or
   because incoming calls are assigned to ports in a round-robin
   fashion, for example, and the second call is simply assigned to
   another RAS.

   The solution to this problem is to provide a mechanism by which a RAS
   can determine if a Multi-link PPP connection is a primary or
   secondary and, if a secondary, where the Bundle Head (the process
   within a RAS which reassembles the PPP fragments transmitted over the
   primary and secondary links) resides.  If the Bundle Head resides on
   a different RAS, a protocol must be used to transfer the PPP
   fragments to the RAS containing the Bundle Head so that the PPP frame
   can be reassembled.

   Section 2 of this document specifies the Discovery Mechanism.
   Section 3 specifies the Transfer Protocol.  Section 4 specifies the
   configuration parameters needed for the Discovery Protocol.

2.  Bundle Head Discovery Mechanism

   When a user dials into a RAS and negotiates Multi-link PPP (MP)
   during the Link Control Protocol (LCP) phase, the RAS must determine
   which one of the following three cases exists:

   1- This is the primary (first) link of the MP connection.  In this
      case, the RAS should create the Bundle Head.

   2- This is a secondary link of the MP connection and the Bundle Head
      resides on this RAS.  In this case, the RAS should add the link to
      the Bundle (standard MP).

   3- This is a secondary link of the MP connection and the Bundle Head
      resides on a different RAS.  In this case, the RAS should
      establish a path (see section 3) to the RAS that has the Bundle
      Head, and use that path to transfer MP fragments.

   In operation, a RAS will make the determination for case 2 first
   (because it is the easiest and requires no communication with other
   RASes.  If the Bundle Head is not local, the Discovery Protocol is
   used to determine where the Bundle Head is, if it exists at all.

Malkin                       Informational                      [Page 2]
RFC 2701                          MMP                     September 1999

2.1 Packet Format

   See "IANA Considerations" (section 6) for UDP port number assignment.

   A Discovery Message has the following format:

      | type |length| random ID  | hash | endpoint ID  |


   type - 2 octets

      Message type: 1-query, 2-response.

   length - 2 octets

      The length (in octets) of the endpoint ID.

   Random ID - 4 octets

      A random identifier generated by the RAS used to resolve
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