Network Working Group Bob Thomas
Internet Draft Cisco Systems, Inc.
Expiration Date: May 2008
Ina Minei
Juniper Networks
November 2007
LDP Typed Wildcard FEC
draft-ietf-mpls-ldp-typed-wildcard-02.txt
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Copyright Notice
Copyright (C) The IETF TRUST (2007).
Abstract
The LDP specification [RFC5036] 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 RFC5036.
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Internet Draft draft-ietf-mpls-ldp-typed-wildcard-02.txt November 2007
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 Capability ...................... 5
6 Typed Wildcard FEC Element for Prefix FEC Element .. 6
7 Host FEC and Wildcard FEC Elements ................. 7
8 IANA Considerations ................................ 7
9 Security Considerations ............................ 7
10 Acknowledgements ................................... 7
11 References ......................................... 8
12 Author Information ................................. 8
13 Intellectual Property Statement .................... 9
14 Full Copyright Statement ........................... 9
1. Introduction
LDP [RFC5036] 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.
RFC5036 specifies two FEC types (Prefix and Wildcard), and other
documents specify additional FEC types; e.g., see [PWE3] [MLDP].
As specified by RFC5036 the Wildcard FEC Element refers to all FECs
relative to an optional constraint. The only constraint RFC5036
specifies is one that limits the scope of the Wildcard FEC Element to
"all FECs bound to a given label".
The RFC5036 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.
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Internet Draft draft-ietf-mpls-ldp-typed-wildcard-02.txt November 2007
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.
This document:
- Addresses the above deficiencies by defining a Typed Wildcard
FEC Element and procedures for its use.
- Specifies use of the LDP capability mechanism [LDPCap] at
session establishment time for informing a peer that an LDP
speaker is capable of handling the Typed Wildcast FEC.
- Specifies the Typed Wildcard FEC Element for the Prefix FEC
Element specified by RFC5036.
Note that this document does not change procedures specified for the
LDP Wildcard FEC Element by RFC5036.
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 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 (IANA) | FEC Element | Len FEC Type | |
| Wildcard | Type | Info | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
~ Additional FEC Type-specific Information ~
| |
| +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Internet Draft draft-ietf-mpls-ldp-typed-wildcard-02.txt November 2007
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.
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. It is the responsibility of the designer
of the FEC Element Type to specify the length and format of any
Additional FEC Type Specific Information.
4. Procedures for the Typed Wildcard FEC Element
It is the responsibility of the designer of the FEC Element Type to
determine whether typed wildcarding makes sense the FEC Element Type.
If typed wildcarding does make sense the specification for the FEC
Element Type MUST include support for it.
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.
An LDP implementation that supports the Typed Wildcard FEC Element
MUST support it for every FEC Element Type implemented for which it
is defined.
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
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Internet Draft draft-ietf-mpls-ldp-typed-wildcard-02.txt November 2007
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
RFC5036. Quoting from RFC5036:
"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
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 Capability
As noted above RFC5056 FEC procedures provide for backward
compatibility with a LSR not supporting the Typed Wildcard FEC
Element. However, they don't provide means for LSR wishing to use
the Typed Wildcard FEC Element to determine whether a peer supports
it other than to send a message that uses the FEC Element and to wait
and see how the peer responds.
An LDP speaker that supports the Typed Wildcard FEC Element MUST
inform its peers of the support by including a Typed Wildcard FEC
Element Capability Parameter [LDPCap] in its Initialization messages.
The Capability Parameter for the Typed Wildcard FEC capability is a
TLV with the following format:
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Internet Draft draft-ietf-mpls-ldp-typed-wildcard-02.txt November 2007
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F|Typed WCard FEC Cap (IANA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved |
+-+-+-+-+-+-+-+-+
where:
U and F bits: As specified by RFC5036.
Typed WCard FEC Cap: TLV code point for the Typed Wildcard FEC
capability (to be assigned by IANA).
S-bit: Must be 1 (indicates that capability is being advertised).
6. Typed Wildcard FEC Element for Prefix FEC Element
RFC5036 defines the Prefix FEC Element but it does not specify a
Typed Wildcard for it. This section specifies the Typed Wildcard FEC
Element for Prefix FEC 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.
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7. Host FEC and Wildcard FEC Elements
There is no need to specify Typed Wildcard FEC Elements for the Host
FEC Element specified by [RFC3036] nor for the Wildcard FEC Element
specified by RFC5036. The [RFC3036] Host FEC Element has been
removed from RFC5036, and the Wildcard FEC Element is untyped by
definition.
8. IANA Considerations
This draft introduces a new LDP FEC Element Type and a new LDP
Capability both of which require code points.
The Typed Wildcard FEC Element requires a code point from the LDP FEC
Type name space. [RFC5036] partitions the FEC TYPE name space into 3
regions: IETF Consensus region, First Come First Served region, and
Private Use region. The authors recommend that the code point 0x05
from the IETF Consensus range be assigned to the Typed Wildcard FEC
Element.
The Typed Wildcard FEC Capability requires a code point from the TLV
Type name space. [RFC5036] partitions the TLV TYPE name space into 3
regions: IETF Consensus region, First Come First Served region, and
Private Use region. The authors recommend that a code point from the
IETF Consensus range be assigned to the Typed Wildcard FEC
Capability.
9. Security Considerations
No security considerations beyond those that apply to the base LDP
specification and described in [RFC5036] apply to use of the Typed
Wildcard FEC Element defined in this document.
10. Acknowledgements
The authors wish to thank Yakov Rehkter for suggesting that the
deficiencies of the Wildcard FEC be addressed.
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11. References
Normative References
[RFC5036] Andersson, L., Minei, I., Thomas, B., Editors, "LDP
Specification", RFC 5036, October 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
[LDPCap] Thomas, B., Aggarwal, S., Aggarwal, R., Le Roux, J.L.,
"LDP Capabilities", draft-ietf-mpls-ldp-capabilities-00, Work in
Progress, May 2007.
[IANA-AF] http://www.iana.org/assignments/address-family-numbers
Informative References
[RFC3036] Andersson, L., Doolan, P., Feldman, N., Fredette, A. and
Thomas, B., "LDP Specification", RFC 3036, January 2001.
[PWE3] Martini, L., Editor, "Pseudowire Setup and Maintenance Using
the Label Distribution Protocol (LDP)", RFC 4447, April 2006.
[MLDP] Minei, I., Wijnands, I., Editors, "Label Distribution
Protocol Extensions for Point-to-Multipoint and Multipoint-to-
Multipoint Label Switched Paths", draft-ietf-mpls-ldp-p2mp-03.txt,
Work in Progress, July 2007.
12. 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
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13. Intellectual Property Statement
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14. 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
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This document and the information contained herein are provided on an
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PURPOSE.
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