Internet Engineering Task Force (IETF) K. Raza
Request for Comments: 6667 S. Boutros
Category: Standards Track C. Pignataro
ISSN: 2070-1721 Cisco Systems
LDP 'Typed Wildcard' Forwarding Equivalence Class (FEC) for
PWid and Generalized PWid FEC Elements
The "Typed Wildcard Forwarding Equivalence Class (FEC) Element"
defines an extension to the Label Distribution Protocol (LDP) that
can be used when requesting, withdrawing, or releasing all label
bindings for a given FEC Element type is desired. 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 Pseudowire Identifier (PWid) (0x80) and Generalized
PWid (0x81) FEC Element types.
Status of This Memo
This is an Internet Standards Track document.
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(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
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Table of Contents
1. Introduction ....................................................2
2. Typed Wildcard for PW FEC Elements ..............................3
3. Applicability Statement .........................................4
4. Operation .......................................................4
4.1. PW Consistency Check .......................................5
4.2. PW Graceful Shutdown .......................................5
4.3. Wildcard PW Status .........................................5
4.4. Typed Wildcard MAC Withdrawal in VPLS ......................6
5. Security Considerations .........................................6
6. Acknowledgments .................................................7
7. References ......................................................7
7.1. Normative References .......................................7
7.2. Informative References .....................................7
An extension to the Label Distribution Protocol (LDP) [RFC5036]
defines the general notion of a "Typed Wildcard Forwarding
Equivalence Class (FEC) Element" [RFC5918]. This can be used when
requesting, releasing, or withdrawing all label bindings for a given
type of FEC Element is desired. 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 the same as described in [RFC5918]
for any Typed Wildcard FEC Element type.
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].
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
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])
Len [FEC Type Info] (one octet): Two. (There is additional
FEC info to scope the Typed Wildcard.)
R bit (Reserved bit): MUST be set to ZERO on transmit and ignored
PW type (15-bits): PW type as specified in [RFC4447]. This field
is used to scope the wildcard FEC operation to limit 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 the "PW Grouping ID TLV" that can be used for
wildcard withdrawal or status messages related to Generalized PWid
FECs. When the Typed Wildcard FEC for Generalized PWid FEC element
is in use, the "PW Grouping ID TLV" MUST NOT be present in the same
message. If present, the receiving Label Switching Router (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
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 PWid Typed Wildcard FEC Elements defined in this document help us
achieve similar functionality as the "Group ID" field or "PW Grouping
ID TLV" for label withdrawal and status notification messages.
Additionally, the Typed Wildcard procedures [RFC5918] provide a more
generalized and comprehensive solution by allowing:
1. Typed Wildcard Label Request messages
2. Label TLVs in label messages to further constrain 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 use of the Typed Wildcard PW FEC Element in any
LDP message that specifies a FEC TLV as a 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]) messages in
the context of LDP PW signaling. When a Typed Wildcard PW FEC
Element is used in an Address Withdraw message for Virtual Private
LAN Service (VPLS) Media Access Control (MAC) address withdrawal, the
MAC List TLV MUST contain an empty list.
The use of Typed Wildcard FEC Elements for PW can be useful under
several scenarios. This section describes some use cases to
illustrate their application. The following use cases consider two
LSR nodes, A and B, with an LDP session between them to exchange
Layer 2 Virtual Private Network (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 learned from LSR B over the LDP
session. To perform this consistency check, LSR A marks all its
learned Generalized PWid FEC bindings from LSR B as stale, and then
sends a Label Request message towards LSR B for the Typed Wildcard
FEC Element for Generalized PWid FEC Element type with the PW type
set to "Wildcard" (0x7FFF). Upon receipt of such a request, LSR B
replays its database related to the 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 (not stale). When replay completes for the Generalized
PWid FEC type, LSR B marks the end of its replay by sending an
End-of-LIB notification [RFC5919] corresponding to the Generalized
PWid FEC Element type. Upon receipt of this notification at LSR A,
any remaining stale PW binding of the Generalized PWid FEC type
learned from the peer LSR B is cleaned up and removed from the
database. This completes the 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
advertised PW bindings are 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 learned from LSR B, LSR A
would send a Label Withdraw message towards LSR B with Typed Wildcard
FEC Elements pertaining to the PWid FEC Element (with PW type set to
0x7FFF) and Generalized PWid FEC Element (with PW type set to
0x7FFF). Upon receipt of such a message, LSR B would delete all PWid
and Generalized PWid bindings learned from LSR A. Afterwards, LSR B
would send Label Release messages corresponding to received Label
Withdraw messages with the Typed FEC Element.
4.3. Wildcard PW Status
The Typed Wildcard FEC Elements for PW FECs can be very useful to
convey PW status amongst LSRs. The Provider Edge (PE) devices can
send the "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 a large
number of PWs.
Using Typed Wildcard FEC Element for a given type of PW FEC Element,
the LSR will need to send only one PW Status Notification message
with the 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 a VPLS environment. These
procedures use the LDP Address Withdraw message containing the FEC
TLV (with the PW FEC element corresponding to the VPLS instance) and
MAC List TLV (to specify addresses to be withdrawn). The procedures
described in RFC 4762 also allow MAC address 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
a VPLS instance corresponding to the PW FEC element in a FEC TLV, and
a MAC List TLV with an empty list of addresses. If there is more
than one VPLS instance on a given PE LSR node, separate Address
Withdraw messages need to be sent by the PE LSR if it wishes to
withdraw MAC addresses for all or a subset of VPLS instances upon
some global failure or configuration. Per-PW (VPLS instance) MAC
Withdraw message may have some scalability implications in a large-
As stated in Section 3, this document allows use of the Typed
Wildcard PW FEC in Address Withdraw messages corresponding to VPLS
MAC Withdrawal. The use 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 those that apply to
specifications [RFC5036], [RFC4447], [RFC4762], [RFC5918], and
[RFC5920] apply to the use of the PW Typed Wildcard FEC Element types
described in this document.
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 use of the Typed Wildcard
PW FEC for VPLS MAC withdrawal.
This document was prepared using 2-Word-v2.0 template.dot.
7.1. Normative References
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, October 2007.
[RFC5918] Asati, R., Minei, I., and B. Thomas, "Label Distribution
Protocol (LDP) 'Typed Wildcard' Forward Equivalence Class
(FEC)", RFC 5918, August 2010.
[RFC5919] Asati, R., Mohapatra, P., Chen, E., and B. Thomas,
"Signaling LDP Label Advertisement Completion", RFC 5919,
[RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
G. Heron, "Pseudowire Setup and Maintenance Using the
Label Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC4762] Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private
LAN Service (VPLS) Using Label Distribution Protocol
(LDP) Signaling", RFC 4762, January 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119, March
7.2. Informative References
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[IANA-PWE3] Internet Assigned Numbers Authority, "Pseudo Wires Name
Cisco Systems, Inc.
2000 Innovation Drive
Ottawa ON K2K-3E8
Cisco Systems, Inc.
3750 Cisco Way
San Jose, CA 95134
Cisco Systems, Inc.
7200 Kit Creek Road
Research Triangle Park, NC 27709-4987