PWE3 Working Group Kamran Raza
Internet Draft Sami Boutros
Intended Status: Standards Track Carlos Pignataro
Expiration Date: August 5, 2012
Cisco Systems
February 6, 2012
LDP Typed Wildcard FEC for PWid and Generalized PWid
FEC Elements
draft-ietf-pwe3-pw-typed-wc-fec-03.txt
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Abstract
The "Typed Wildcard Forwarding Equivalence Class (FEC) Element"
defines an extension to the Label Distribution Protocol (LDP) that
can be used when it is desired to request or withdraw or release all
label bindings for a given FEC Element type. However, a typed
wildcard FEC element must be individually defined for each FEC
element type. This specification defines the typed wildcard FEC
elements for the PWid (0x80) and Generalized PWid (0x81) FEC element
types.
Conventions used in this document
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 RFC-2119 [RFC2119].
Table of Contents
1. Introduction .................................................. 3
2. Typed Wildcard for PW FEC Elements ............................ 3
3. Applicability Statement ....................................... 4
4. Operation ..................................................... 5
4.1. PW Consistency Check ...................................... 5
4.2. PW Graceful Shutdown ...................................... 5
4.3. Wildcard PW Status ........................................ 6
4.4. Typed Wildcard MAC Withdrawal in VPLS ..................... 6
5. Security Considerations ....................................... 7
6. IANA Considerations ........................................... 7
7. Acknowledgments ............................................... 7
8. References .................................................... 7
8.1. Normative References ...................................... 7
8.2. Informative References .................................... 8
Authors' Addresses ............................................... 8
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1. Introduction
An extension [RFC5918] to the Label Distribution Protocol (LDP)
[RFC5036] defines the general notion of a "Typed Wildcard Forwarding
Equivalence Class (FEC) Element". This can be used when it is
desired to request all label bindings for a given type of FEC
Element, or to release or withdraw all label bindings for a given
type of FEC element. However, a typed wildcard FEC element must be
individually defined for each type of FEC element.
[RFC4447] defines the "PWid FEC Element" and "Generalized PWid FEC
Element", but does not specify the Typed Wildcard format for these
elements. This document specifies the format of the Typed Wildcard
FEC Element for the "PWid FEC Element" and "Generalized PWid FEC
Element". The procedures for Typed Wildcard processing for PWid and
Generalized PWid FEC Elements are same as described in [RFC5918] for
any typed wildcard FEC Element type.
2. Typed Wildcard for PW FEC Elements
The format of the Typed Wildcard FEC Element for PWid and
Generalized PWid 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Typed Wcard=0x5| Type=PW FEC | Len = 2 |R| PW type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . |
+-+-+-+-+-+-+-+-+
Figure 1: Format of Typed Wildcard FEC Element for PW FEC Element
Types
Where:
Typed Wcard (one octet): Typed Wildcard FEC element type (0x05)
as specified in [RFC5918]
[FEC Element] Type (one octet): PW FEC Element type:
PWid: (type 0x80 [RFC4447])
Generalized PWid: (type 0x81 [RFC4447])
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Len [FEC Type Info] (one octet): Two. (i.e. there is additional
FEC info to scope the Typed Wildcard)
R bit (Reserved bit): Must be set to ZERO on transmit and ignored
on receipt.
PW type (15-bits): PW type as specified in [RFC4447]. This field
is used to scope the wildcard FEC operation to limit to all
PWs of a given type. This MUST be set to "Wildcard" type
(0x7FFF), as defined in [IANA-PWE3], when referring PWs of
all types (see Section 4 for its usage).
[RFC4447] defines "PW Grouping ID TLV" that can be used for wildcard
withdrawal or status messages related to Generalized PWid FECs. When
Typed Wildcard FEC for Generalized PWid FEC element is in use, "PW
Grouping ID TLV" MUST NOT be present in the same message. If found
present, the receiving LSR MUST ignore this TLV silently, and process
the rest of the message.
3. Applicability Statement
The Typed wildcard FEC Elements defined in this document for the
PWid and Generalized PWid FEC Elements provide a finer degree of
granularity when compared to the wildcard FEC mechanics defined in
[RFC5036].
The PWid FEC Element as defined in [RFC4447] contains a Group ID
field. This field is defined as an arbitrary 32-bit value that
represents a group of PWs, and is used to create groups in the PW
space, including potentially a single group of all PWs for a given
FEC Element type. This grouping enables an LSR to send "wildcard"
label withdrawals and/or status notification messages corresponding
to a PW group upon physical port failures. Similarly, [RFC4447]
defines the "PW Grouping ID TLV" used in the same fashion for the
Generalized PWid FEC Element.
The PW Typed Wildcard FEC elements defined in this document help us
achieve the similar functionality as "Group ID" field or "PW Grouping
ID TLV" for label withdrawal and status notification messages;
Additionally, the Typed Wildcard procedures [RFC5918] also provide
more generalized and comprehensive solution by allowing:
1. Typed-Wildcard Label Request messages
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2. Label TLV in label messages to further constraint the wildcard to
all FECs of the specified FEC type [and its specific filter] that
are also bound to the specified label.
This document allows the use of Typed Wildcard PW FEC Element in any
LDP message that specifies a FEC TLV as mandatory or optional
parameter of the message. In addition to LDP label messages, this
also applies to Notification messages (containing PW Status) and
Address Withdraw (for MAC address withdrawal [RFC4762]) in the
context of LDP PW signaling. When a Typed Wildcard PW FEC element is
used in a Address Withdraw message for VPLS MAC address withdrawal,
the MAC List TLV MUST contain an empty list.
4. Operation
The use of Typed Wildcard FEC elements for PW can be useful under
several scenarios. This section describes some use cases to
illustrate their usage. The following use cases consider two LSR
nodes, A and B, with LDP session between them to exchange L2VPN PW
bindings.
4.1. PW Consistency Check
A user may request a control plane consistency check at LSR A for
the Generalized PWid FEC bindings that it had learnt from LSR B over
LDP session. To perform this consistency check, LSR A marks all its
learnt Generalized PWid FEC bindings from LSR B as stale, and then
sends a Label Request message towards LSR B for Typed Wildcard FEC
element for Generalized PWid FEC element type with PW type set to
"Wildcard" (0x7FFF). Upon receipt of such request, LSR B replays its
database related to Generalized PWid FEC element using one or more
Label Mapping messages. As a PW binding is received at LSR A, the
associated binding state is marked as refreshed (no stale). When
replay completes for Generalized PWid FEC type, LSR B marks end of
its replay by sending End-of-LIB notification [RFC5919]
corresponding to Generalized PWid FEC element type. Upon receipt of
this notification at LSR A, any remaining stale PW binding of
Generalized PWid FEC type learnt from the peer LSR B, is cleaned up
and removed from the database. This completes consistency check with
LSR B at LSR A for Generalized PWid FEC type.
4.2. PW Graceful Shutdown
It may be desirable to perform shutdown/removal of existing PW
bindings advertised towards a peer in a graceful manner - i.e. all
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advertised PW bindings to be removed from a peer without session
flap. For example, to request a graceful delete of the PWid FEC and
Generalized PWid FEC bindings at LSR A learnt from LSR B, LSR A
would send a Label Withdraw message towards LSR B with Typed
Wildcard FEC elements pertaining to PWid FEC element (with PW type
set to 0x7FFF) and Generalized PWid FEC element (with PW type set to
0x7FFF). Upon receipt of such message, LSR B will delete all PWid
and Generalized PWid bindings learnt from LSR A. Afterwards, LSR B
would send Label Release messages corresponding to received Label
Withdraw messages with Typed FEC element.
4.3. Wildcard PW Status
The Typed Wildcard FEC Elements for PW FECs can be very useful when
used to convey PW status amongst LSRs. The PE devices can send "PW
Status TLV" in an LDP Notification message to indicate PW status
(i.e., a Pseudowire Status Code denoting for example a particular
fault) to their remote peers [RFC4447]. In case of a global failure
affecting all PWs, an LSR typically sends one PW Status LDP
Notification message per PW. This per PW Status message has
scalability implications in a large-scale network with large number
of PWs.
Using Typed Wildcard FEC Element for given type of PW FEC Element,
the LSR will need to send only one PW Status Notification message
with Typed Wildcard PW FEC specified to notify about the common
status applicable to all PWs as scoped by the PW Typed Wildcard FEC.
4.4. Typed Wildcard MAC Withdrawal in VPLS
[RFC4762] defines a pseudowire based solution to implement Virtual
Private LAN Service (VPLS). Section 6.2 of RFC-4762 describes MAC
Withdrawal procedures and extensions in an VPLS environment. These
procedures use LDP Address Withdraw message containing FEC TLV (with
PW FEC element corresponding to the VPLS instance) and MAC List TLV
(to specify addresses to be withdrawn). RFC-4762 procedures also
allow MAC addresses withdrawal wildcarding for a given VPLS instance.
Using RFC-4762 procedures, a PE LSR can withdraw all MAC addresses
for a given VPLS instance by sending an Address Withdraw message with
VPLS instance corresponding PW FEC element in a FEC TLV, and MAC List
TLV with an empty list of addresses. If there are more than one VPLS
instance on a given PE LSR node, separate Address Withdraw messages
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will need to be sent by PE LSR if it wishes to withdraw MAC addresses
for all or subset of VPLS instances upon some global failure or
configuration. This per PW (VPLS instance) MAC Withdraw messages may
have some scalability implications in large-scale network.
As stated in section 3, this document allows use of Typed Wildcard PW
FEC in Address Withdraw messages corresponding to VPLS MAC
Withdrawal. The usage of PW Typed Wildcard FEC enhances the scope of
MAC withdrawal beyond just a single VPLS instance, and allows a PE
node to wildcard withdraw all MAC addresses for:
o all VPLS instances; or
o all VPLS instances corresponding to a given PW type.
5. Security Considerations
No new security considerations beyond that apply to the base LDP
specification [RFC5036], [RFC4447], [RFC4762], and [RFC5920] apply to
the use of the PW Typed Wildcard FEC Element types described in this
document.
6. IANA Considerations
None.
7. Acknowledgments
The authors would like to thank Eric Rosen, Reshad Rahman, Siva
Sivabalan, and Zafar Ali for their review and valuable comments. We
also acknowledge Daniel Cohn for suggesting the use of Typed Wildcard
PW FEC for VPLS MAC withdrawal.
This document was prepared using 2-Word-v2.0 template.dot.
8. References
8.1. Normative References
[RFC5036] L. Andersson, I. Minei, and B. Thomas, "LDP Specification",
RFC 5036, September 2007.
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[RFC5918] R. Asati, I. Minei, and B. Thomas, "LDP Typed Wildcard
Forwarding Equivalence Class", RFC 5918, August 2010.
[RFC5919] R. Asati, P. Mohapatra, E. Chen, and B. Thomas, "Signaling
LDP Label Advertisement Completion", RFC 5919, August 2009.
[RFC4447] L. Martini, E. Rosen, El-Aawar, T. Smith, and G. Heron,
"Pseudowire Setup and Maintenance using the Label
Distribution Protocol", RFC 4447, April 2006.
[RFC4762] M. Lasserre, and V. Kompella, "Virtual Private LAN Service
(VPLS) Using Label Distribution Protocol (LDP) Signaling",
RFC 4762, January 2007.
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
8.2. Informative References
[RFC5920] L. Fang (Editor), et al., "Security Framework for MPLS and
GMPLS Networks", RFC 5920, July 2010.
[IANA-PWE3] Internet Assigned Numbers Authority, "Pseudo Wires Name
Spaces (PWE3)", http://www.iana.org/assignments/pwe3-
parameters, May 2011.
Authors' Addresses
Kamran Raza
Cisco Systems, Inc.,
2000 Innovation Drive,
Ottawa, ON K2K-3E8, Canada.
Email: skraza@cisco.com
Sami Boutros
Cisco Systems, Inc.,
3750 Cisco Way,
San Jose, CA 95134, USA.
Email: sboutros@cisco.com
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Carlos Pignataro
Cisco Systems, Inc.,
7200 Kit Creek Road,
Research Triangle Park, NC 27709-4987, USA.
Email: cpignata@cisco.com
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