Network Working Group Bob Thomas
Internet Draft Cisco Systems, Inc.
Expiration Date: November 2007
Ina Minei
Juniper Networks
May 2007
LDP Typed Wildcard FEC
draft-ietf-mpls-ldp-typed-wildcard-01.txt
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Copyright Notice
Copyright (C) The IETF TRUST (2007).
Abstract
The LDP specification [RFC3036] for the Wildcard FEC element has
several deficiencies. This document corrects those deficiencies. In
addition, it specifies the Typed Wildcard FEC for the Prefix FEC
Element Type defined in RFC3036.
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Table of Contents
1 Introduction .......................................... 2
2 Specification Language ................................ 3
3 The Typed Wildcard FEC Element ........................ 3
4 Procedures for the Typed Wildcard FEC Element ......... 4
5 Typed Wildcard FEC Element for RFC3036 Prefix FEC Element 5
6 RFC3036 Host and Wildcard FEC Elements ................ 5
7 IANA Considerations ................................... 5
8 Security Considerations ............................... 6
9 Acknowledgements ...................................... 6
10 References ............................................ 6
11 Author Information .................................... 7
12 Intellectual Property Statement ....................... 7
13 Full Copyright Statement .............................. 8
1. Introduction
LDP [RFC3036] distributes labels for Forwarding Equivalence Classes
(FECs). LDP uses FEC TLVs in LDP messages to specify FECs. An LDP
FEC TLV includes 1 or more FEC Elements. A FEC element includes a
FEC type and an optional type-dependent value.
RFC3036 specifies two FEC types (Wildcard and Prefix), and other
documents specify additional FEC types; e.g., see [PWE3] [MLDP].
As specified in RFC3036 the Wildcard FEC Element refers to all FECs
relative to an optional constraint. The only constraint RFC3036
specifies is one that limits the scope of the Wildcard FEC Element to
"all FECs bound to a given label".
The RFC3036 specification of the Wildcard FEC Element has the
following deficiencies which limit its utility:
1. The Wildcard FEC Element is untyped. There are situations
where it would be useful to be able to refer to all FECs of a
given type.
2. Use of the Wildcard FEC Element is limited to Label Withdraw
and Label Release messages only. There are situations where it
would be useful in Label Request messages.
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This document addresses these deficiencies by defining a Typed
Wildcard FEC Element and procedures for its use. Note that this
document does not change procedures specified for the LDP Wildcard
FEC Element by RFC3036.
2. Specification Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. The Typed Wildcard FEC Element
The Typed Wildcard FEC Element refers to all FECs of a given type
relative to an optional constraint. The constraint, if present, is
determined from the context in which the Typed Wildcard FEC Element
appears.
The format of the Typed Wildcard FEC Element is:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Typed (IANA) | FEC Element | Len FEC Type | |
| Wildcard | Type | Info | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| Additional FEC Type-specific Information |
| +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Typed Wildcard: One octet FEC Element type to be assigned by IANA.
FEC Element Type: One octet FEC Element Type that specifies the
FEC Element Type to be wildcarded.
Len FEC Type Info: One octet that specifies the length of the FEC
Type Specific information field. MUST be 0 if there is no
Additional FEC Type-specific Information.
Additional FEC Type-specific Information: Additional information
specific to the FEC Element Type required to fully specify the
Typed Wildcard.
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Specification of the length and format of Additional FEC Type
Specific Information for particular FEC Element Types is outside of
the scope of this document.
4. Procedures for the Typed Wildcard FEC Element
It is the responsibility of the designer of the FEC Element Type to
specify whether typed wildcarding is required for the FEC Element
Type. When typed wildcarding is supported for a FEC Element Type it
is the responsibility of the designer to specify the length and
format of any Additional FEC Type Specific Information.
When a FEC TLV contains a Typed Wildcard FEC Element the Typed
Wildcard FEC Element MUST be the only FEC Element in the TLV.
An LDP implementation that supports the Typed Wildcard FEC Element
MUST support its use in Label Request, Label Withdraw and Label
Release messages.
Receipt of a Label Request message with a FEC TLV containing a Typed
Wildcard FEC Element is interpreted as a request to send a Label
Mapping for all FECs of the type specified by the FEC Element type
field in the Typed Wildcard FEC Element encoding.
An LDP implementation that supports the Typed Wildcard FEC Element
MUST support the following constraints whenever a Typed Wildcard FEC
appears in a Label Withdraw or Label Release message:
1. If the message carries an optional Label TLV the Typed Wildcard
FEC Element refers to all FECs of the specified FEC type bound to
the specified label.
2. If the message has no Label TLV the Typed Wildcard FEC Element
refers to all FECs of the specified FEC type.
Backwards compatibility with a router not supporting the Typed
Wildcard FEC element is ensured by the FEC procedures defined in
RFC3036. Quoting from RFC3036:
"If it" [an LSR] "encounters a FEC Element type it cannot decode,
it SHOULD stop decoding the FEC TLV, abort processing the
message containing the TLV, and send an "Unknown FEC"
Notification message to its LDP peer signaling an error."
A router receiving a FEC TLV containing a Typed Wildcard FEC element
for a FEC Element Type that it either doesn't support or for a FEC
Element Type that doesn't support the use of wildcarding MUST stop
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decoding the FEC TLV, abort processing the message containing the
TLV, and send an "Unknown FEC" Notification message to its LDP peer
signaling an error.
5. Typed Wildcard FEC Element for RFC3036 Prefix FEC Element
RFC3036 defines the Prefix FEC Element but it does not specify a
Typed Wildcard for it. This section specifies the Typed Wildcard FEC
Element for RFC3036 Prefix Elements.
The format of the Prefix FEC Typed Wildcard FEC ("Prefix FEC
Wildcard" for short) is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Typed WCard | Prefix (2) | 2 | Address... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...Family |
+-+-+-+-+-+-+-+-+
Address Family: Two octet quantity containing a value from ADDRESS
FAMILY NUMBERS in [IANA-AF].
The procedures of Section 4 apply to the Prefix FEC Wildcard.
6. RFC3036 Host and Wildcard FEC Elements
There is no need to specify Typed Wildcard FEC Elements for the Host
and Wildcard FEC Elements specified by RFC3036. The RFC3036 Host FEC
Element has been removed from rfc3036bis [RFC3036bis], and the
Wildcard FEC Element is untyped by definition.
7. IANA Considerations
The Typed Wildcard FEC Element requires a code point from the LDP FEC
Type Name Space. IANA manages the FEC TYPE name space as recommended
by the following from [RFC3036]:
"FEC Type Name Space
The range for FEC types is 0 - 255.
Following the policies outlined in [RFC3036], FEC types in the
range 0 - 127 are allocated through an IETF Consensus action,
types in the range 128 - 191 are allocated as First Come First
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Served, and types in the range 192 - 255 are reserved for Private
Use."
The authors recommend that the code point 0x05 from the IETF
Consensus range be assigned to the Typed Wildcard FEC Element.
8. Security Considerations
No security considerations beyond those that apply to the base LDP
specification and described in [RFC3036] apply to use of the Typed
Wildcard FEC Element defined in this document.
9. Acknowledgements
The authors wish to thank Yakov Rehkter for suggesting that the
deficiencies of the Wildcard FEC be addressed.
10. References
Normative References
[RFC3036] Andersson, L., Doolan, P., Feldman, N., Fredette, A. and
Thomas, B., "LDP Specification", RFC 3036, January 2001.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
[IANA-AF] http://www.iana.org/assignments/address-family-numbers
Informative References
[PWE3] Martini, L., Editor, "Pseudowire Setup and Maintenance Using
the Label Distribution Protocol (LDP)", RFC 4447, April 2006.
[MLDP] Minei, I., Wijnamds, I., Editors, "Label Distribution
Protocol Extensions for Point-to-Multipoint and Multipoint-to-
Multipoint Label Switched Paths", draft-ietf-mpls-ldp-p2mp-02.txt,
Work in Progress, October 2006.
[RFC3036bis] Andersson, L., Minei, I., Thomas, B., Editors, "LDP
Specification", draft-ietf-mpls-rfc3036bis-04.txt, Work in
Progress, September 2006.
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11. Author Information
Bob Thomas
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough MA 01719
Email: rhthomas@cisco.com
Ina Minei
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
Email: ina@juniper.net
12. Intellectual Property Statement
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13. Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
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