draft-ietf-mpls-cosfield-def-02.txt   draft-ietf-mpls-cosfield-def-03.txt 
Network Working Group L. Andersson Network Working Group L. Andersson
Internet-Draft Acreo AB Internet-Draft Acreo AB
Intended status: Standards Track June 11, 2008 Updates: RFC 3032, RFC 3270, RFC July 4, 2008
Expires: December 13, 2008 5129, RFC 3272, RFC 3443, RFC
3469, RFC 3564, RFC 3985, RFC
4182, RFC 4364, RFC 4379, RFC
4448, RFC 4761 (if approved)
Intended status: Standards Track
Expires: January 5, 2009
"EXP field" renamed to "CoS Field" "EXP field" renamed to "CoS Field"
draft-ietf-mpls-cosfield-def-02.txt draft-ietf-mpls-cosfield-def-03.txt
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Abstract Abstract
The early MPLS documents defined the form of a the MPLS Label Stack The early MPLS documents defined the form of the MPLS Label Stack
entry. This include a three bit field called the "EXP field". The entry. This include a three bit field called the "EXP field". The
exact use of this field was not defined by these documents, except to exact use of this field was not defined by these documents, except to
state that it is to be "reserved for experimental use". state that it was to be "reserved for experimental use".
Although the intended use of the EXP field was as a "Class of Although the intended use of the EXP field was as a "Class of
Service" field, it was not named the "Class of Service" (CoS) field Service" field, it was not named the "Class of Service" (CoS) field
by these early documents because the use of such a CoS field was not by these early documents because the use of such a CoS field was not
considered to be sufficiently defined. Today a number of standards considered to be sufficiently defined. Today a number of standards
documents define its usage as a CoS field. . documents define its usage as a CoS field. .
To avoid misunderstanding about how this field may be used this To avoid misunderstanding about how this field may be used, this
document re-introduces the name "CoS field" for this field. In doing document changes the name of the field to the "CoS field". In doing
so it also updates documents that define the current usee of the EXP so it also updates documents that define the current use of the EXP
this field. this field.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Details of change . . . . . . . . . . . . . . . . . . . . . . 5 2. Details of change . . . . . . . . . . . . . . . . . . . . . . 5
2.1. RFC 3032 . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. RFC 3032 . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. RFC 3270 . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. RFC 3270 . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. RFC 5129 . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3. RFC 5129 . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Use of the CoS field . . . . . . . . . . . . . . . . . . . . . 8 2.4. The Scope of this Change . . . . . . . . . . . . . . . . . 8
4. IANA considerations . . . . . . . . . . . . . . . . . . . . . 9 3. Use of the CoS field . . . . . . . . . . . . . . . . . . . . . 9
5. Security considerations . . . . . . . . . . . . . . . . . . . 10 4. IANA considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 5. Security considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.2. Informative references . . . . . . . . . . . . . . . . . . 12 7.1. Normative References . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.2. Informative references . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 14 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
1. Introduction 1. Introduction
The format of a MPLS label stack entry is defined by RFC 3032 The format of a MPLS label stack entry is defined by RFC 3032
[RFC3032], includes three bit field called "EXP field". The exact [RFC3032], include a three bit field called the "EXP field". The
use of this field is not defined by RFC 3032 leaves,, except to state exact use of this field is not defined by RFC 3032 leaves, except to
that it is to be "reserved for experimental use". state that it is to be "reserved for experimental use".
The EXP field, from the start, was intended to carry "Class of The EXP field, from the start, was intended to carry "Class of
Service" information, the field was actually called the "Class of Service" information. The field was actually called the "Class of
Service field" in the early versions of the working group document Service field" in the early versions of the working group document
that was publshed as RFC 3032. However at the time that RFC 3032 was that was publshed as RFC 3032. However at the time that RFC 3032 was
published the exact usage of this "Class of Service" field was not published the exact usage of this "Class of Service" field was not
agreed and the field was designated as "Experimental use". agreed and the field was designated as "Experimental use".
The designation "for Experimental use" has lead other Standards The designation "for Experimental use" has lead other Standards
Development Organizations (SDO) and implementors to the assume that Development Organizations (SDO) and implementors to the assume that
it possible to use the field for other purposes than Class of it possible to use the field for other purposes than Class of
Service. This document changes the name of the field to clearly Service. This document changes the name of the field to clearly
indicate its use. indicate its use.
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The use of the EXP field was first defined in RFC 3270 [RFC3270] The use of the EXP field was first defined in RFC 3270 [RFC3270]
where a method to define a variant of DiffServ LSPs called EXP- where a method to define a variant of DiffServ LSPs called EXP-
Inferred-PSC LSP (E-LSPs) were specified. Inferred-PSC LSP (E-LSPs) were specified.
The use of the EXP field as defined in RFC 3270 has been further The use of the EXP field as defined in RFC 3270 has been further
extended in RFC 5129 [RFC5129], where methods for explicit congestion extended in RFC 5129 [RFC5129], where methods for explicit congestion
marking in MPLS are defined. marking in MPLS are defined.
The defintions of how the EXP field are used are perfectly clear in The defintions of how the EXP field are used are perfectly clear in
RFC 3270 and RFC 5129. However, these RFCs do not explicitly state RFC 3270 and RFC 5129. However, these RFCs do not explicitly state
they update 3032, and it is not captured in the RFC respository. they update RFC 3032, and this fact is not captured in the RFC
This document updates RFC 3032, RFC 3270 and RFC 5129 to clarify the respository. This document updates RFC 3032, RFC 3270 and RFC 5129
intended usage of the CoS field. to clarify the intended usage of the CoS field.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Details of change 2. Details of change
The three RFCs are now updated according to the following. The three RFCs are now updated according to the following.
2.1. RFC 3032 2.1. RFC 3032
The RFC 3032 states on page 3: RFC 3032 states on page 4:
3. Experimental Use 3. Experimental Use
This three-bit field is reserved for experimental use. This three-bit field is reserved for experimental use.
This paragraph is now changed to: This paragraph is now changed to:
3. Class of Service (CoS) field 3. Class of Service (CoS) field
This three-bit field is used to carry Class of Service information This three-bit field is used to carry Class of Service information
and the change of the name is applicable to all places it occurs and the change of the name is applicable to all places it occurs
in IETF RFCs and other IETF documents. in IETF RFCs and other IETF documents.
The definition of how to use the CoS field has been updated by RFC The definition of how to use the CoS field has been updated by RFC
3270 and RFC 5129. 3270 and RFC 5129.
In Figure 1 on page 3 in RFC3032 the format of label stack entries is
specified as:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Label
| Label | Exp |S| TTL | Stack
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Entry
Label: Label Value, 20 bits
Exp: Experimental Use, 3 bits
S: Bottom of Stack, 1 bit
TTL: Time to Live, 8 bits
Figure 1
Figure 1 in RFC 3032 is now changed to match the change of name of
the Cos field to:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Label
| Label | CoS |S| TTL | Stack
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Entry
Label: Label Value, 20 bits
CoS: Class of Service field, 3 bits
S: Bottom of Stack, 1 bit
TTL: Time to Live, 8 bits
Figure 1
2.2. RFC 3270 2.2. RFC 3270
RFC 3270 says on page 6: RFC 3270 says on page 6:
1.2 EXP-Inferred-PSC LSPs (E-LSP) 1.2 EXP-Inferred-PSC LSPs (E-LSP)
A single LSP can be used to support one or more OAs. Such LSPs A single LSP can be used to support one or more OAs. Such LSPs
can support up to eight BAs of a given FEC, regardless of how many can support up to eight BAs of a given FEC, regardless of how many
OAs these BAs span. With such LSPs, the EXP field of the MPLS OAs these BAs span. With such LSPs, the EXP field of the MPLS
Shim Header is used by the LSR to determine the PHB to be applied Shim Header is used by the LSR to determine the PHB to be applied
skipping to change at page 8, line 5 skipping to change at page 8, line 25
header, but the IP header says the endpoints are not CoS-capable, header, but the IP header says the endpoints are not CoS-capable,
the edge router (or penultimate router, if using penultimate hop the edge router (or penultimate router, if using penultimate hop
popping) drops the packet. We recommend this scheme, which we popping) drops the packet. We recommend this scheme, which we
call `per-domain ECT checking', and define it more precisely in call `per-domain ECT checking', and define it more precisely in
the following section. Its chief drawback is that it can cause the following section. Its chief drawback is that it can cause
packets to be forwarded after encountering congestion only to be packets to be forwarded after encountering congestion only to be
dropped at the egress of the MPLS domain. The rationale for this dropped at the egress of the MPLS domain. The rationale for this
decision is given in Section 8.1. This scheme is an update to RFC decision is given in Section 8.1. This scheme is an update to RFC
3032 [RFC3032] and RFC 3270 [RFC3270]. 3032 [RFC3032] and RFC 3270 [RFC3270].
2.4. The Scope of this Change
There are several places in the RFCs that has explicitly updated by
this document that refrence the "Exp field", sometimes they refer to
the field as "Exp bits", "EXP bits" and "EXP". In all those
instances the references SHOULD be taken to reference the CoS field.
There are also other RFCs, e.g. RFC 3272 [RFC3272], RFC 3443
[RFC3443], RFC 3469 [RFC3469], RFC 3564 [RFC3564], RFC 3985
[RFC3985], RFC 4182 [RFC4182], RFC 4364 [RFC4364], RFC 4379
[RFC4379], RFC 4448 [RFC4448] and RFC 4761 [RFC4761] that references
the "Exp field", sometimes they refer to the field as "Exp bits",
"EXP bits" and "EXP". For all RFCs, including but not limited to
those mentioned in this paragraph, such references SHOULD be taken to
reference the CoS field.
3. Use of the CoS field 3. Use of the CoS field
Due to the limited number of bits the particular use of the bits is Due to the limited number of bits the particular use of the bits is
intended to be flexible - including the definition of various QoS and intended to be flexible - including the definition of various QoS and
ECN functions. ECN functions.
Current implementations look at the CoS field with and without label Current implementations look at the CoS field with and without label
context and the CoS field may be copied to the labels that are pushed context and the CoS field may be copied to the label stack entries
onto the label stack. This is to avoid the pushed labels having a that are pushed onto the label stack. This is to avoid the pushed
different CoS field. label stack entries having a different CoS field.
CoS and ECN funtions may rewrite all or some of the bits. CoS and ECN funtions may rewrite all or some of the bits.
4. IANA considerations 4. IANA considerations
There are no request for IANA allocation of code points in this There are no request for IANA allocation of code points in this
document. document.
5. Security considerations 5. Security considerations
This document only changes the name of one field in the MPLS Shim This document only changes the name of one field in the MPLS Shim
Header and thus does not introduce any new security considerations. Header and thus does not introduce any new security considerations.
6. Acknowledgments 6. Acknowledgments
The author would like to thank Stewart Bryant, Bruce Davie, George The author would like to thank Stewart Bryant, Bruce Davie, George
Swallow, and Francois Le Faucheur for their input to and review of Swallow, and Francois Le Faucheur for their input to and review of
the current document. the current document.
The author also like to thanks George Swallow, Khatri Paresh and Phil The author also like to thanks George Swallow, Khatri Paresh and Phil
Bedard for their help with grammar and spelling. Bedard for their help with grammar and spelling, and a special thanks
to Adrian Farrel for a careful review and help trawling the RFC-sea
for RFCs that references the EXP field.
7. References 7. References
7.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001. Encoding", RFC 3032, January 2001.
[RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen, [RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi- P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
Protocol Label Switching (MPLS) Support of Differentiated Protocol Label Switching (MPLS) Support of Differentiated
Services", RFC 3270, May 2002. Services", RFC 3270, May 2002.
[RFC3272] Awduche, D., Chiu, A., Elwalid, A., Widjaja, I., and X.
Xiao, "Overview and Principles of Internet Traffic
Engineering", RFC 3272, May 2002.
[RFC3443] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing
in Multi-Protocol Label Switching (MPLS) Networks",
RFC 3443, January 2003.
[RFC3469] Sharma, V. and F. Hellstrand, "Framework for Multi-
Protocol Label Switching (MPLS)-based Recovery", RFC 3469,
February 2003.
[RFC3564] Le Faucheur, F. and W. Lai, "Requirements for Support of
Differentiated Services-aware MPLS Traffic Engineering",
RFC 3564, July 2003.
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC4182] Rosen, E., "Removing a Restriction on the use of MPLS
Explicit NULL", RFC 4182, September 2005.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
[RFC4448] Martini, L., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, April 2006.
[RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling",
RFC 4761, January 2007.
[RFC5129] Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion [RFC5129] Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion
Marking in MPLS", RFC 5129, January 2008. Marking in MPLS", RFC 5129, January 2008.
7.2. Informative references 7.2. Informative references
[Shayman] Shayman, M. and R. Jaeger, University of Michigan, "Using [Shayman] Shayman, M. and R. Jaeger, University of Michigan, "Using
ECN to Signal Congestion Within an MPLS Domain", Work in ECN to Signal Congestion Within an MPLS Domain", Work in
Progress, November 2000.", <http://www.watersprings.org/ Progress, November 2000.", <http://www.watersprings.org/
pub/id/draft-shayman-mpls-ecn-00.txt/>. pub/id/draft-shayman-mpls-ecn-00.txt/>.
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