Internet DRAFT - draft-boutros-pwe3-mpls-tp-mac-wd
draft-boutros-pwe3-mpls-tp-mac-wd
Network Working Group S. Sivabalan
Internet-Draft S. Boutros
Intended status: Standards Track Cisco Systems, Inc.
Expires: August 12, 2014 H. Shah
Ciena Corp.
S. Aldrin
Huawei Technologies.
February 08, 2014
MAC Address Withdrawal over Static Pseudowire
draft-boutros-pwe3-mpls-tp-mac-wd-03.txt
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.
Requirements 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].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on August 12, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. MAC Withdraw OAM Message . . . . . . . . . . . . . . . . . . 3
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Operation of Sender . . . . . . . . . . . . . . . . . . . 5
4.2. Operation of Receiver . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
An LDP-based MAC Address Withdrawal Mechanism is specified in
[RFC4762] 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. [MAC-OPT] describes an
optimized MAC 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. This is analogous to the problem and solution described in
[RFC4762] where PW OAM message has been introduced to carry PW
status TLV using in-band PW Associated Channel. In this document, we
propose to use PW OAM message to withdraw MAC address(es) learned via
static PW.
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2. Terminology
The following terminologies are used in this document:
ACK: Acknowledgement for MAC withdraw message.
LDP: Label Distribution Protocol.
MAC: Media Access Control.
PE: Provide Edge Node.
MPLS: Multi Protocol Label Switching.
PW: PseudoWire.
PW OAM: PW Operations, Administration and Maintenance.
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 [RFC6478]. 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
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. The PW OAM message header is exactly the same as what is
defined in [RFC6478]. Since the MAC withdrawal PW OAM message is not
refreshed forever. 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 [MAC-OPT] when
static PWs are deployed in H-VPLS and PBB-VPLS scenarios. The first
2 bits of the sequence number TLV are reserved and MUST be set to 0
on transmit and ignored on receipt.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved |0xZZ MAC Withdraw OAM Message |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | TLV Length |A|R| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Res| Sequence Number TLV (TBD) | Sequence Number TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MAC List TLV |
~ MAC Flush Parameter TLV (optional) ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: MAC Address Withdraw PW OAM Packet Format
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 are governed by [RFC4762], and the corresponding rules
of MAC Flush Parameter TLV are governed by [MAC-OPT].
"TLV Length" is the total length of all TLVs in the message, and
"Sequence Number TLV Length" is the length of the sequence number
field.
A single bit (called A-bit) is set to indicate if a MAC withdraw
message is for ACK. Also, ACK does not include MAC TLV(s).
Only half of the sequence number space is used. Modular arithmetic
is used to detect wrapping of sequence number. When sequence number
wraps, all MAC addresses are flushed and the sequence number is
reset.
A single bit (called R-bit) is set to indicate if the sender is
requesting reset of the sequence numbers. The sender sets this bit
when the Pseudowire is restarted and has no local record of send and
expected receive sequence number.
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.
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4.1. 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 transmit sequence number is initialized to 1 at the onset.
The sender expects an ACK from the receiver within a time interval
which we call "Retransmit Time" which can be either a default (1
second) or configured value. If the ACK does not arrive within the
Retransmit Time, the sender retransmits the message with the same
sequence number as the original message. The retransmission is
ceased anytime when ACK is received or after three retries. This
avoids unended retransmissions in the absence of acknowledgements.
In addition, if during the period of retransmission, if a need to
send a new MAC withdraw message with updated sequence number arises
then retransmission of the older unacknowledged withdraw message is
suspended and retransmit time for the new sequence number is
initiated. In essence, sender engages in retrasmission logic only
for the latest send withdraw message for a given PW.
In the event that a Pseudowire was deleted and re-added or the router
is restarted with configuration, the local node may lose information
about the send sequence number of previous incarnation. This becomes
problematic for the remote peer as it will continue to ignore the
received MAC withdraw messages with lower sequence numbers. In such
cases, it is desirable to reset the sequence numbers at both ends of
the Pseudowire. The 'R' reset bit is set in the first MAC withdraw
to notify the remote peer to reset the send and receive sequence
numbers. The 'R' bit must be cleared in subsequent MAC withdraw
messages after the acknowledgement is received
4.2. Operation of Receiver
Each PW is associated with a register 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 value in the register, the MAC
address(es) contained in the MAC TLV(s) is/are removed, and the
register is updated with the received sequence number. The receiver
sends an ACK whose sequence number is the same as that in the
received message.
If the sequence number in the received message is smaller than or
equal to the value in the register, the MAC TLV(s) is/are not
processed. However, an ACK with the received sequence number MUST be
sent as a response. The receiver processes the ACK message as an
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acknowledgement for all the MAC withdraw messages sent up to the
sequence number present in the ACK message and terminates
retransmission.
As mentioned above, since only half of the sequence number space is
used, the receiver MUST use modular arithmetic to detect wrapping of
the sequence number.
A MAC withdraw message with 'R' bit set MUST be processed by
resetting the send and receive sequence number first. The rest of
MAC withdraw message processing is performed as described above. The
acknowledgement is sent with 'R' bit cleared.
5. IANA Considerations
The proposed mechanism requests IANA to a assign new channel type
(recommended value 0x0028) 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.
6. References
6.1. Normative References
[MAC-OPT] Dutta, P., Balus, F., Stokes, O., and G. Calvinac, "LDP
Extensions for Optimized MAC Address Withdrawal in
H-VPLS", draft-ietf-l2vpn-vpls-ldp-mac-opt-10.txt (work in
progress), January 2014.
[RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service
(VPLS) Using Label Distribution Protocol (LDP) Signaling",
RFC 4762, January 2007.
[RFC6478] Martini, L., Swallow, G., Heron, G., and M. Bocci,
"Pseudowire Status for Static Pseudowires", RFC 6478, May
2012.
6.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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Authors' Addresses
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
Email: msiva@cisco.com
Sami Boutros
Cisco Systems, Inc.
170 West Tasman Dr.
San Jose, CA 95134
US
Email: sboutros@cisco.com
Himanshu Shah
Ciena Corp.
3939 North First Street
San Jose, CA 95134
US
Email: hshah@ciena.com
Sam Aldrin
Huawei Technologies.
2330 Central Express Way
Santa Clara, CA 95051
US
Email: aldrin.ietf@gmail.com
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