Internet DRAFT - draft-christian-gre-over-clnp
draft-christian-gre-over-clnp
Internet Engineering Task Force P. Christian,
INTERNET-DRAFT Nortel Networks
Category: Informational May 2001
Expires: November 2001
Generic Routing Encapsulation over CLNS networks
<draft-christian-gre-over-clnp-02.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
Internet Drafts are working documents of the Internet Engineering
Task Force (IETF), its Areas, and its Working Groups. Note that
other groups may also distribute working documents as Internet
Drafts.
Internet Drafts are draft documents valid for a maximum of six
months. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet
Drafts as reference material or to cite them other than as a
"working draft" or "work in progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind.
Distribution of this draft is unlimited.
Christian Expires November 2001 1
Internet Draft May 2001
Generic Routing Encapsulation over CLNS Networks
Abstract
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.
This document proposes a method for transporting an arbitrary
protocol over a CLNS network using GRE.
This may then be used as a method to tunnel IPv4 or IPv6 over CLNS.
This document is an Independent Submission. Comments should be
submitted to christi@nortelnetworks.com.
1. Introduction
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.
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.
Christian Expires November 2001 2
Internet Draft May 2001
Generic Routing Encapsulation over CLNS Networks
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
exists.
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.
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].
Christian Expires November 2001 3
Internet Draft May 2001
Generic Routing Encapsulation over CLNS Networks
For convenience the structure of a Data PDU is reproduced from
ISO/IEC 8473-1 [6] below:-
Octet
----------------------------------------
| Network Layer Protocol Identifier | 1
----------------------------------------
| Length Indicator | 2
----------------------------------------
| Version/Protocol Id Extension | 3
----------------------------------------
| Lifetime | 4
----------------------------------------
| SP | MS | E/R | Type | 5
----------------------------------------
| Segment Length | 6,7
----------------------------------------
| Checksum | 8,9
----------------------------------------
| Destination Address Length Indicator | 10
----------------------------------------
| | 11
| Destination Address |
| | m-1
----------------------------------------
| Source Address Length Indicator | m
----------------------------------------
| | m+1
| Source Address |
| | n-1
----------------------------------------
| Data Unit Identifier | n,n+1
----------------------------------------
| Segment Offset | n+2,n+3
----------------------------------------
| Total Length | n+4,n+5
----------------------------------------
| | n+6
| Options |
| | p
----------------------------------------
| | p+1
| Data ( GRE packet ) |
| | z
----------------------------------------
Christian Expires November 2001 4
Internet Draft May 2001
Generic Routing Encapsulation over CLNS Networks
4. NSAP selector (N-SEL) value.
Transport of GRE packets is a new type of Network Service (NS) user.
Different Network Service users are identified by using different
NSAP selector bytes also known as N-SEL bytes.
This is a similar concept to the use of the IP Protocol Type used in
IP packets.
Whilst it is not strictly necessary for all vendors to use the same
N-SEL values, they must use the same N-SEL value for it to be
possible for one vendor's CLNS device or network element to initiate
a GRE tunnel which is then terminated on a different vendor's CLNS
device.
Although N-SEL values (other than zero) are not defined in CLNS/CLNP
standards, some are defined when CLNS is used in SONET networks by
Bellcore GR-253-CORE [3] whilst others are in common use.
As the IP protocol number for GRE is 47, as defined in RFC 1702 [2],
and as 47 is not commonly used as an N-SEL value, it is suggested
that 47 (decimal) should be used as an N-SEL value to indicate to
the CLNS stack that the Data portion of the Data Type PDU contains a
GRE packet.
The N-SEL byte should be set to 47 (decimal) in both the source
address and the destination address of the CLNP PDU.
The N-SEL value of 47 should indicate only that the payload is GRE,
and the device or network element that transmits the PDU should use
the GRE header to indicate what protocol (for example IPv4 or IPv6)
is encapsulated within the GRE packet in conformance with RFC 2784
[1]. Similarly the device or network element that receives the PDU
should then inspect the GRE header to ascertain what protocol is
contained within the GRE packet in conformance with RFC 2784 [1].
5. Segmentation Permitted (SP) value.
It is recommended that the SP flag in all CLNP PDUs containing GRE
packets should be set.
If the SP flag is not set, and a CLNP PDU is too large for a
particular link, then a CLNS device or network element will drop the
PDU. The originator of the packet that is inside the GRE packet will
not have visibility of the packet loss or the reason for the packet
loss, and a black hole may form.
6. Interaction with Path MTU Discovery (PMTU), RFC 1191 [7].
A tunnel entry point for a GRE tunnel should treat IP packets that
are bigger than the MTU size of the GRE tunnel as per RFC 1191 [7].
Christian Expires November 2001 5
Internet Draft May 2001
Generic Routing Encapsulation over CLNS Networks
If the oversize IP packet that is about to enter the GRE tunnel does
not have its DonĘt Fragment (DF) bit set then it should be
fragmented before entering the tunnel.
If the oversize IP packet that is about to enter the GRE tunnel has
its DF bit set then the packet should be discarded, and an ICMP
unreachable error message (in particular the "fragmentation needed
and DF set" code) should be sent back to the originator of the
packet as described in RFC 1191 [7].
7. Security Considerations
CLNS and GRE do not provide any security when employed in the way
recommended in this document.
If security is required, then it must be provided by other methods
and applied to the payload protocol before it is transported by GRE
over CLNS.
Christian Expires November 2001 6
Internet Draft May 2001
Generic Routing Encapsulation over CLNS Networks
8. References
[1] Farinacci, D., Li, T., Hanks, S., Meyer, D. and P. Traina,
"Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.
[2] Hanks, S., Li, T., Farinacci, D. and P. Traina, "Generic
Routing Encapsulation over IPv4", RFC 1702, October 1994.
[3] Bellcore Publication GR-253-Core "Synchronous Optical Network
(SONET) Transport Systems: Common Generic Criteria", January 1999
[4] ITU-T Recommendation G.784 "Synchronous Digital Hierarchy
(SDH) management", June 1999
[5] Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1700,
October 1994
[6] "Information technology - Protocol for providing the
connectionless-mode network service", ISO/IEC 8473-1, 1994
[7] Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191,
November 1990.
9. Acknowledgements
Chris Murton, Paul Fee, Mike Tate for their contribution in writing
this document.
10. Author's Address
Philip Christian
Nortel Networks Harlow Laboratories
London Road, Harlow,
Essex, CM17 9NA UK
Email: christi@nortelnetworks.com
Christian Expires November 2001 7
Internet Draft May 2001
Generic Routing Encapsulation over CLNS Networks
11. Copyright Notice
Copyright (C) The Internet Society 2001. All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organisations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Christian Expires November 2001 8
