MPLS Working Group Bob Thomas
Internet Draft
Intended status: Standards Track
Expires: Feb 2010 Ina Minei
Juniper Networks
Rajiv Asati
Cisco Systems
September 5, 2009
LDP Typed Wildcard FEC
draft-ietf-mpls-ldp-typed-wildcard-04.txt
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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.
Table of Contents
1. Introduction...................................................3
2. Specification Language.........................................4
3. The Typed Wildcard FEC Element.................................4
4. Procedures for the Typed Wildcard FEC Element..................5
5. Typed Wildcard FEC Capability..................................6
6. Typed Wildcard FEC Element for Prefix FEC Element..............7
7. Typed Wildcard FEC Element for Host and Wildcard FEC Elements..8
8. IANA Considerations............................................8
9. Security Considerations........................................8
10. Acknowledgments...............................................8
11. References....................................................9
11.1. Normative References.....................................9
11.2. Informative References...................................9
Author's Addresses...............................................10
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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 [RFC4447] [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.
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 [RFC5561] 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.
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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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Typed (IANA) | FEC Element | Len FEC Type | |
| Wildcard | Type | Info | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
~ Additional FEC Type-specific Information ~
| |
| +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 Typed Wildcard FEC Element
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.
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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.
This document discusses two instances of Typed Wildcard FEC Elements
in section 6 and 7.
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
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:
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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 [RFC5561] in its Initialization
messages.
The Capability Parameter for the Typed Wildcard FEC capability is a
TLV with the following format:
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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 |
+-+-+-+-+-+-+-+-+
Figure 2 Typed Wildcard FEC Capability format
Where:
U and F bits : MUST be 1 and 0 respectively as per section
3 of LDP Capabilities [RFC5561].
Typed WCard FEC Cap : TLV code point 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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Typed Wcard | Prefix (2) | 2 | Address... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...Family |
+-+-+-+-+-+-+-+-+
Figure 3 Format of Prefix FEC Element using Typed Wildcard
Where:
Address Family: Two octet quantity containing a value from ADDRESS
FAMILY NUMBERS in [IANA-AF].
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The procedures of Section 4 apply to the Prefix FEC Wildcard.
7. Typed Wildcard FEC Element for Host 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 IANA assignment -
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 [RFC5036] and further described in [MPLSsec] apply to
use of the Typed Wildcard FEC Elements as described in this document.
10. Acknowledgments
The authors would like to thank Yakov Rekhter for suggesting that the
deficiencies of the Wildcard FEC be addressed.
This document was prepared using 2-Word-v2.0.template.dot.
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11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5036] Andersson, L., Minei, I., and Thomas, B., "LDP
Specification", RFC 5036, October 2007.
[RFC5561] Thomas, B., Aggarwal, S., Aggarwal, R., Le Roux, J.L., "LDP
Capabilities", RFC5561, May 2007.
11.2. Informative References
[RFC3036] Andersson, L., Doolan, P., Feldman, N., Fredette, A. and
Thomas, B., "LDP Specification", RFC 3036, January 2001.
[RFC4447] Martini, L., Editor, "Pseudowire Setup and Maintenance
Using the label Distribution Protocol (LDP)", RFC4447,
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-07.txt, Work in Progress, July 2009.
[MPLSsec] Fang, L., "Security Framework for MPLS and GMPLS Networks",
draft-ietf-mpls-mpls-and-gmpls-security-framework-06, Work
in Progress, July 13 2009.
[IANA-AF] http://www.iana.org/assignments/address-family-numbers.
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Author's Addresses
Ina Minei
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
Email: ina@juniper.net
Bob Thomas
Email: bobthomas@alum.mit.edu
Rajiv Asati
Cisco Systems,
7025-6 Kit Creek Rd, RTP, NC, 27709-4987
Email: rajiva@cisco.com
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