Network Working Group Siva Sivabalan (Ed.)
Internet Draft Sami Boutros (Ed.)
Intended status: Standards Track Neil McGill
Expires: September 4, 2012
Cisco Systems, Inc.
March 4, 2012
MAC Address Withdrawal over Static Pseudowire
draft-boutros-l2vpn-mpls-tp-mac-wd-00.txt
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Abstract
This document specifies a mechanism to signal MAC address withdrawal
notification using PW Associated Channel (ACH). Such notification is
useful when statically provisioned PWs are deployed in VPLS/H-VPLS
environment.
This document is a product of a joint Internet Engineering Task
Force(IETF) / International Telecommunication Union
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Telecommunication Standardization Sector (ITU-T) effort to include
an MPLS Transport Profile within the IETF MPLS and PWE3
architectures to support the capabilities and functionalities of a
packet transport network.
Table of Contents
1. Introduction...................................................2
2. Terminology....................................................3
3. MAC Withdraw OAM Message.......................................3
4. Operation......................................................5
4.1.1. Operation of Sender..................................5
4.1.2. Operation of Receiver................................5
5. Security Considerations........................................6
6. IANA Considerations............................................6
7. References.....................................................6
7.1. Normative References......................................6
7.2. Informative References....................................6
Author's Addresses................................................7
Full Copyright Statement..........................................7
Intellectual Property Statement...................................8
1. Introduction
An LDP-based MAC Address Withdrawal Mechanism is specified in
RFC4762 [2] to remove dynamically learned MAC addresses when the
source of those addresses can no longer forward traffic. This is
accomplished by sending an LDP Address Withdraw Message with a MAC
List TLV containing the MAC addressed to be removed to all other PEs
over LDP sessions. When the number of MAC addresses to be removed is
large, empty MAC List TLV may be used. [3] describes an optimized AC
withdrawal mechanism which can be used to remove only the set of MAC
addresses that need to be re-learned in H-VPLS networks. The
solution also provides optimized MAC Withdrawal operations in PBB-
VPLS networks.
A PW can be signaled via LDP or can be statically provisioned. In
the case of static PW, LDP based MAC withdrawal mechanism cannot be
used.
In this document, we propose to use PW OAM message to withdraw MAC
address(es) learned via static PW.
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This document is a product of a joint Internet Engineering Task
Force (IETF) / International Telecommunication Union
Telecommunication Standardization Sector (ITU-T) effort to include
an MPLS Transport Profile within the IETF MPLS and PWE3
architectures to support the capabilities and functionalities of a
packet transport network.
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 [1].
2. Terminology
ACK: Acknowledgement.
LDP: Label Distribution Protocol.
MAC: Media Access Control
MPLS: Multi Protocol Label Switching.
OAM: MPLS Operations, Administration and Maintenance.
PE: Provide Edge Node.
PW: PseudoWire.
TLV: Type, Length, and Value.
VPLS: Virtual Private LAN Services.
3. MAC Withdraw OAM Message
LDP provides a reliable packet transport for control plackets for
dynamic PWs. This can be contrasted with static PWs which rely on
re-transmission and acknowledgments (ACK) for reliable OAM packet
delivery as described in [4]. The proposed solution for MAC
withdrawal over static PW also relies on re-transmissions and ACKs.
However, ACK is mandatory. A given MAC withdrawal notification is
sent as a PW OAM message, and the sender keeps re-transmitting the
message until it receives an ACK for that message. Once a receiver
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successfully remove MAC address(es) in response to a MAC address
withdraw OAM message, it should not unnecessarily remove MAC
address(es) upon getting refresh message(s). To facilitate this, the
proposed mechanism uses sequence number, and defines a new TLV to
carry the sequence number.
The format of the MAC address withdraw OAM message is shown in
Figure 1. A MAC address withdraw OAM message MUST contain a
"Sequence Number TLV" otherwise the entire message is dropped. It
may contain MAC Flush Parameter TLVs defined in [3] when static PWs
are deployed in H-VPLS and PBB-VPLS scenarios. The sequence number
TLV has U (Unknown) and F (Forward) bits set to 1 and 0 respectively
so that if a receiver does not recognize the TLV, it drops the whole
message.
In this section, MAC List TLV and MAC Flush Parameter TLV are
collectively referred to as "MAC TLV(s)". The processing rules of
MAC List TLV is governed by [2], and the corresponding rules of MAC
Flush Parameter TLV are governed by [3].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | 0xZZ PW MAC-WD OAM Message |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | TLV Length |A| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Sequence Number TLV (TBD) | TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MAC List TLV |
~ MAC Flush Parameter TLV (optional) ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: MAC Address Withdraw PW OAM Packet Format.
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Only half of the sequence number space is used. Modular arithmetic
is used to detect wrapping of sequence number. When sequence number
wraps (i.e., when it becomes 0), all MAC addresses are flushed and
the sequence number is reset.
An ACK for MAC withdraw OAM message is the same as the one shown in
Figure 1 except that:
. A-bit is set.
. It does not include MAC TLV(s).
. It must include the Sequence Number TLV.
4. Operation
This section describes how the initial MAC withdraw OAM messages are
sent and retransmitted, as well as how the messages are processed
and retransmitted messages are identified.
4.1.1. Operation of Sender
Each PW is associated with a counter to keep track of the sequence
number of the transmitted MAC withdrawal messages. Whenever a node
sends a new set of MAC TLVs, it increments the transmitted sequence
number counter, and include the new sequence number in the message.
The sender expects an ACK from the receiver within a time interval
which we call "Retransmit Time" which can be either a default or
configured value. If the ACK arrives within the Retransmit Time, the
sender assumes that the message transmission is successful.
Otherwise, it retransmits the message with the same sequence number
as the original message.
4.1.2. Operation of Receiver
Each PW is associated with a counter to keep track of the sequence
number of the MAC withdrawal message received last. Whenever a MAC
withdrawal message is received, and if the sequence number on the
message is greater than the receive counter, the MAC address(es)
contained in the MAC TLV(s) is/are removed, and the receive counter
is incremented. The receiver sends an ACK whose sequence number is
the same as the received message.
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If the sequence number in the received message is smaller than or
equal to the receive counter, the MAC TLV(s) is/are not processed.
However, an ACK whose sequence number is the same as the received
message is sent.
5. Security Considerations
This document does not introduce any additional security
constraints.
6. IANA Considerations
The proposed mechanism requests IANA to a assign new channel type
(recommended value 0x0023) from the registry named "Pseudowire
Associated Channel Types". The description of the new channel type
is "Pseudowire MAC Withdraw OAM Channel".
IANA needs to create a new registry for Pseudowire Associated
Channel TLVs, and create an entry for "Sequence Number TLV". The
recommended value is 0x0001.
7. References
7.1. Normative References
[1] Bradner. S, "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March, 1997.
7.2. Informative References
[2] Mark Lassere, et. al, "Virtual Private LAN Service (LAN) Using
Label Distribution Protocol (LDP) Signaling", RFC4762, January
2007.
[3] Pranjal Kumar Dutta, et. al, "LDP Extensions for Optimized MAC
Address Withdrawal in H-VPLS", draft-ietf-l2vpn-vpls-ldp-mac-
opt-02.txt (work in progress), July 2010.
[4] Luca Martini, et. al, "Pseudowire Status for Static
Pseudowires", draft-ietf-pwe3-static-pw-status-00.txt (work in
progress), February 2010.
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Author's Addresses
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario, K2K 3E8
Canada
Email: msiva@cisco.com
Sami Boutros
Cisco Systems, Inc.
3750 Cisco Way
San Jose, California 95134
USA
Email: sboutros@cisco.com
Neil McGill
Cisco Systems, Inc.
7100-9 Kit Creek Road
PO Box 14987
Research Triangle Park, North Carolina 27709-4987
USA
Email: nmcgill@cisco.com
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