Generic Routing Encapsulation over CLNS Networks
RFC 3147

Document Type RFC - Informational (July 2001; No errata)
Author Philip Christian 
Last updated 2013-03-02
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Network Working Group                                       P. Christian
Request for Comments: 3147                               Nortel Networks
Category: Informational                                        July 2001

           Generic Routing Encapsulation over CLNS Networks

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 (2001).  All Rights Reserved.


   This document proposes a method for transporting an arbitrary
   protocol over a CLNS (Connectionless Network Service) network using
   GRE (Generic Routing Encapsulation).  This may then be used as a
   method to tunnel IPv4 or IPv6 over CLNS.

1. Introduction

   RFC 2784 Generic Routing Encapsulation (GRE) [1] provides a standard
   method for transporting one arbitrary network layer protocol over
   another arbitrary network layer protocol.

   RFC 1702 Generic Routing Encapsulation over IPv4 networks [2]
   provides a standard method for transporting an arbitrary network
   layer protocol over IPv4 using GRE.

   However no standard method exists for transporting other network
   layer protocols over CLNS.  This causes lack of interoperability
   between different vendors' products as they provide solutions to
   migrate from CLNS networks to IP networks.  This is a problem
   specifically in, but not limited to, the context of management
   networks for SONET and SDH networks elements.

   Large networks exist for the purpose of providing management
   communications for SONET and SDH network elements.  Standards
   Bellcore GR-253-CORE [3] and ITU-T G.784 [4] mandate that these
   networks are based on CLNS.

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RFC 3147    Generic Routing Encapsulation over CLNS Networks   July 2001

   Many vendors have already started to offer SONET and SDH products
   that are managed by IP instead of CLNS and a general migration from
   CLNS towards IP is anticipated within the industry.

   Part of any migration strategy from CLNS to IP should provide for the
   co-existence of both CLNS managed and IP managed network elements in
   the same network.

   Such a migration strategy should foresee the need to manage existing
   CLNS managed network elements that become isolated by a new IP
   network.  Such a scenario may be tackled by tunnelling CLNP PDUs over
   IP using the existing GRE standard RFC 2784 [1] and informational RFC
   1702 [2].  Networks have already been deployed that use this method.

   Such a migration strategy should also foresee the need to manage new
   IP managed network elements that are installed on the far side of
   existing CLNS managed network.  Such a scenario requires a method for
   tunnelling IP over CLNS.

2. GRE over CLNS advantages

   Using GRE to tunnel IP over CLNS offers some advantages.

      In the absence of a standard for tunnelling IP over CLNS, GRE as
      specified in RFC 2784 [1] is the most applicable standard that

      The move from CLNS to IP comes at a time when IP is itself
      migrating from IPv4 to IPv6.  GRE defines a method to tunnel any
      protocol that has an Ethernet Protocol Type.  Therefore by
      defining a method for CLNS to transport GRE, a method will then
      exist for CLNS to transport any other protocol that has an
      Ethernet Protocol Type defined in RFC 1700 [5].  Thus GRE over
      CLNS can be used to tunnel both IPv4 and IPv6.

      GRE is already commonly used to tunnel CLNP PDUs over IP and so
      using GRE to tunnel IP over CLNS gives a common approach to
      tunnelling and may simplify software within network elements that
      initiate and terminate tunnels.

   The only disadvantage of using GRE is the extra minimum of four bytes
   that will be used between CLNP header and IP payload packet.  Given
   the large size of CLNP headers this will not make a  significant
   difference to the performance of any network that has IP over CLNP
   PDUs present on it.

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RFC 3147    Generic Routing Encapsulation over CLNS Networks   July 2001

3. Transporting GRE packets over CLNS.

   It is suggested that GRE should be transported over CLNS at the
   lowest layer possible, which is as a transport layer protocol over
   the network layer.  This can be achieved by placing the entire GRE
   packet inside a CLNP Data Type PDU (DT PDU) as data payload.

   The GRE packet is a GRE packet as defined in RFC 2784 [1], in other
   words GRE header plus payload packet.

   Data payload is the part of a Data PDU that is described as "Data" in
   the structure of a Data PDU in ISO/IEC 8473-1 [6].

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