One document matched: draft-ietf-l2vpn-vpls-ldp-mac-opt-03.txt
Differences from draft-ietf-l2vpn-vpls-ldp-mac-opt-02.txt
L2VPN Working Group Pranjal Kumar Dutta
Florin Balus
Internet Draft Alcatel-Lucent
Intended status: Standard
Expires: January 21, 2011 Olen Stokes
Extreme Networks
Geraldine Calvignac
France Telecom
October 25, 2010
LDP Extensions for Optimized MAC Address Withdrawal in H-VPLS
draft-ietf-l2vpn-vpls-ldp-mac-opt-03.txt
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Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Abstract
[RFC4762] describes a mechanism to remove or unlearn MAC addresses
that have been dynamically learned in a VPLS Instance for faster
convergence on topology change. The procedure also removes MAC
addresses in the VPLS that do not require relearning due to such
topology change.
This document defines an enhancement to the MAC Address Withdrawal
procedure with empty MAC List [RFC4762], which enables a Provider
Edge(PE) device to remove only the MAC addresses that need to be
relearned.
Additional extensions to [RFC4762] MAC Withdrawal procedures are
specified to provide optimized MAC flushing for the PBB-VPLS
specified in [PBB-VPLS Model].
Table of Contents
1.1. Conventions used in this document.........................3
2. Introduction...................................................3
3. Problem Description............................................5
3.1. MAC Flush in regular H-VPLS...............................5
3.2. Black holing issue in PBB-VPLS............................7
4. Solution description...........................................8
4.1. MAC Flush Optimization for regular H-VPLS.................8
4.1.1. PE-ID TLV Format.....................................8
4.1.2. Application of PE-ID TLV in Optimized MAC Flush.....11
4.1.3. PE-ID TLV Processing Rules..........................11
4.1.4. Optimized MAC Flush Procedures......................12
4.2. LDP MAC Withdraw Extensions for PBB-VPLS.................14
4.2.1. MAC Flush Parameters TLV format.....................14
4.2.2. MAC Flush Parameters TLV Processing Rules...........16
5. Security Considerations.......................................17
6. IANA Considerations...........................................18
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7. Acknowledgments...............................................18
8. References....................................................18
8.1. Normative References.....................................18
8.2. Informative References...................................18
Author's Addresses...............................................19
1.1. 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.
This document uses the terminology defined in [PBB-VPLS Model],
[RFC5036], [RFC4447] and [RFC4762]. Throughout this document VPLS
means the emulated bridged LAN service offered to a customer. H-VPLS
means the hierarchical connectivity or layout of MTU-s and PE devices
offering the VPLS [RFC4762]. The terms spoke node and MTU-s in H-VPLS
are used interchangeably.
2. Introduction
A method of Virtual Private LAN Service (VPLS), also known as
Transparent LAN Service (TLS) is described in [RFC4762]. A VPLS is
created using a collection of one or more point-to-point pseudowires
(PWs) [RFC4664] configured in a flat, full-mesh topology. The mesh
topology provides a LAN segment or broadcast domain that is fully
capable of learning and forwarding on Ethernet MAC addresses at the
PE devices.
This VPLS full mesh core configuration can be augmented with
additional non-meshed spoke nodes to provide a Hierarchical VPLS (H-
VPLS) service [RFC4762].
[PBB-VPLS Model] describes how Provider Backbone Bridging (PBB) can
be integrated with VPLS to allow for useful PBB capabilities while
continuing to avoid the use of MSTP in the backbone. The combined
solution referred to as PBB-VPLS results in better scalability in
terms of number of service instances, PWs and C-MACs that need to be
handled in the VPLS PEs.
A MAC Address Withdrawal mechanism for VPLS is described in [RFC4762]
to remove or unlearn MAC addresses for faster convergence on topology
change in resilient H-VPLS topologies.
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An example of usage of the MAC Flush mechanism is the dual-homed
H-VPLS where an edge device termed as MTU-s is connected to two PE
devices via primary spoke PW and backup spoke PW respectively. Such
redundancy is designed to protect against the failure of primary
spoke PW or primary PE device. When the MTU-s switches over to the
backup PW, it is required to flush the MAC addresses learned in the
corresponding VSI in peer PE devices participating in full mesh, to
avoid black holing of frames to those addresses. Note that forced
switchover to backup PW can be also performed at MTU-s
administratively due to maintenance activities on the primary spoke
PW. When the backup PW is made active by the MTU-s, it triggers LDP
Address Withdraw Message with a list of MAC addresses to be flushed.
The message is forwarded over the LDP session(s) associated with the
newly activated PW. In order to minimize the impact on LDP
convergence time and scalability when a MAC List TLV contains a large
number of MAC addresses, many implementations use a LDP Address
Withdraw Message with an empty MAC List. Throughout this document the
term MAC Flush Message is used to specify LDP Address Withdraw
Message with empty MAC List described in [RFC4762] unless specified
otherwise.
As per the MAC Address Withdrawal processing rules in [RFC4762] a PE
device on receiving a MAC flush message removes all MAC addresses
associated with the specified VPLS instance (as indicated in the FEC
TLV) except the MAC addresses learned over the newly activated PW.
The PE device further triggers a MAC flush message to each remote PE
device connected to it in the VPLS full mesh.
This method of MAC flushing is modeled after Topology Change
Notification (TCN) in Rapid Spanning Tree Protocol (RSTP)[802.1w].
When a bridge switches from a failed link to the backup link, the
bridge sends out a TCN message over the newly activated link. The
upstream bridge upon receiving this message flushes its entire MAC
addresses except the ones received over this link and sends the TCN
message out of its other ports in that spanning tree instance. The
message is further relayed along the spanning tree by the other
bridges. When a PE device in the full-mesh of H-VPLS receives a MAC
flush message it also flushes MAC addresses which are not affected
due to topology change, thus leading to unnecessary flooding and
relearning. This document describes the problem and a solution to
optimize the MAC flush procedure in [RFC4762] so it flushes only the
set of MAC addresses that require relearning when topology changes in
H-VPLS. The solution proposed in this document is generic and is
applicable when MS-PWs are used in interconnecting PE devices in
H-VPLS.
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[PBB-VPLS Model] describes how PBB can be integrated with VPLS to
allow for useful PBB capabilities while continuing to avoid the use
of MSTP in the backbone. The combined solution referred as PBB-VPLS
results in better scalability in terms of number of service
instances, PWs and C-MACs that need to be handled in the VPLS PEs.
This document describes also extensions to LDP MAC Flush procedures
described in [RFC4762] required to build desirable capabilities to
PBB-VPLS solution.
Section 3 covers the problem space. Section 4 describes the solution
and the required TLV extensions.
3. Problem Description
3.1. MAC Flush in regular H-VPLS
Figure 1 describes a dual-homed H-VPLS scenario for a VPLS instance
where the problem with the existing MAC flush method in [RFC4762] is
explained.
PE-1 PE-3
+--------+ +--------+
| | | |
| -- | | -- |
Customer Site 1 | / \ |------------------| / \ |->
CE-1 /------| \ s/ | | \S / |
\ primary spoke PW | -- | /------| -- |
\ / +--------+ / +--------+
\ (MTU-s)/ | \ / |
+--------+/ | \ / |
| | | \ / |
| -- | | \ / |
| / \ | | H-VPLS Full Mesh Core|
| \S / | | / \ |
| -- | | / \ |
/+--------+\ | / \ |
/ backup spoke PW | / \ |
/ \ +--------+ \--------+--------+
CE-2 \ | | | |
Customer Site 2 \------| -- | | -- |
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| / \ |------------------| / \ |->
| \s / | | \S / |
| -- | | -- |
+--------+ +--------+
PE-2 PE-4
Figure 1: Dual homed MTU-s in two tier hierarchy H-VPLS
In Figure 1, the MTU-s is dual-homed to PE-1 and PE-2. Only the
primary spoke PW is active at MTU-s, thus PE-1 is acting as the
active device to reach the full mesh in the VPLS instance. The MAC
addresses of nodes located at access sites (behind CE1 and CE2) are
learned at PE-1 over the primary spoke PW. PE-2, PE-3 and PE-4 learn
those MAC addresses on their respective mesh PWs terminating to PE-1.
When MTU-s switches to the backup spoke PW and activates it, PE-2
becomes the active device to reach the full mesh core. Traffic
entering the H-VPLS from CE-1 and CE-2 is diverted by the MTU-s to
the backup spoke PW. For faster convergence MTU-s may desire to
unlearn or remove the MAC addresses that have been learned in the
upstream VPLS full-mesh through PE-1. MTU-s may send a MAC flush
message to PE-2 once the backup PW has been made active. As per the
processing rules defined in [RFC4762], PE-2 flushes the MAC addresses
learned in the VPLS from the PWs terminating at PE-1, PE-3 and PE-4.
In the H-VPLS core, PE devices are connected in full mesh unlike the
spanning tree connectivity in bridges. So the MAC addresses that
require flushing and relearning at PE-2 are only the MAC addresses
those have been learned on the PW connected to PE-1.
PE-2 further relays MAC flush messages to all other PE devices in the
full mesh. Same processing rule applies at all those PE devices. For
example, at PE-3 all of the MAC addresses learned from the PWs
connected to PE-1 and PE-4 are flushed and relearned subsequently. As
the number of PE devices in the full-mesh increases, the number of
unaffected MAC addresses flushed in a VPLS instance also increases,
thus leading to unnecessary flooding and relearning. With large
number of VPLS instances provisioned in the H-VPLS network topology
the amount of unnecessary flooding and relearning increases.
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3.2. Black holing issue in PBB-VPLS
In PBB-VPLS solution a B-component VPLS (B-VPLS) may be used as
infrastructure for one or more I-component instances. B-VPLS control
plane (LDP Signaling) replaces I-component control plane throughout
the MPLS core. This is raising an additional challenge related to
black hole avoidance in the I-component domain as described in this
section. Figure 2 describes the case of a CE device (node A) dual-
homed to two I-component instances located on two PBB-VPLS PEs (PE1
and PE2).
IP/MPLS Core
+--------------+
|PE2 |
+----+ |
|PBB | +-+ |
_ |VPLS|---|P| |
S/+----+ /+-+\ |PE3
/ +----+ / \+----+
+---+/ |PBB |/ +-+ |PBB | +---+
CMAC X--|CE |---|VPLS|---|P|--|VPLS|---|CE |--CMAC Y
+---+ A +----+ +-+ +----+ +---+
A |PE1 | B
| |
+--------------+
Figure 2: PBB Black holing Issue - CE Dual-Homing use case
The link between PE1 and CE A is active (marked with A) while the
link between CE A and PE2 is in Standby/Blocked status. In the
network diagram CMAC X is one of the MAC addresses located behind CE
A in the customer domain, CMAC Y is behind CE B and the BVPLS
instances on PE1 are associated with backbone MAC (BMAC) B1 and PE2
with BMAC B2.
As the packets flow from CMAC X to CMAC Y through PE1 of BMAC B1, the
remote PEs participating in the IVPLS (for example, PE3) will learn
the CMAC X associated with BMAC B1 on PE1. Under failure of the link
between CE A and PE1 and activation of link to PE2, the remote PEs
(for example, PE3) will black-hole the traffic destined for customer
MAC X to BMAC B1 until the aging timer expires or a packet flows from
X to Y through the PE B2. This may take a long time (default aging
timer is 5 minutes) and may affect a large number of flows across
multiple I-components.
A possible solution to this issue is to use the existing LDP MAC
Flush as specified in [RFC4762] to flush in the BVPLS domain the BMAC
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associated with the PE where the failure occurred. This will
automatically flush the CMAC to BMAC association in the remote PEs.
This solution though has the disadvantage of producing a lot of
unnecessary MAC flush in the B-VPLS domain as there was no failure or
topology change affecting the Backbone domain.
A better solution is required to propagate the I-component events
through the backbone infrastructure (B-VPLS) in order to flush only
the customer MAC to BMAC entries in the remote PBB-VPLS PEs. As there
are no IVPLS control plane exchanges across the PBB backbone,
extensions to B-VPLS control plane are required to propagate the I-
component MAC Flush events across the B-VPLS.
4. Solution description
4.1. MAC Flush Optimization for regular H-VPLS
The basic principle of the optimized MAC flush mechanism is explained
with reference to Figure 1. On switching over to the backup spoke PW
when MTU-s triggers MAC flush message to PE-2, it also communicates
the unique PW endpoint identifier (PE-ID) in PE-1, the formerly
active PE device. In VPLS a PW terminates on a Virtual Switching
Instance (VSI) in a PE device. The PE-ID is relayed in all the
subsequent MAC flush messages triggered by PE-2 to its peer PE
devices in the full mesh. Each PE device that receives the message
identifies the VPLS (From FEC TLV) and its respective PW that
terminates in PE-1 (from PE-ID). Thus the PE device flushes only the
MAC addresses learned from that PW connected to PE-1.
This section defines a PW Endpoint Identifier (PE-ID) TLV for LDP
[RFC5036]. The PE-ID TLV carries the unique identifier of a generic
PW endpoint.
4.1.1. PE-ID TLV Format
The encoding of PE-ID TLV follows standard LDP TLV encoding in
[RFC5036]. A PE-ID TLV contains a list of one or more PE-ID Elements.
Its encoding is:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| PE-ID TLV (0x0405) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PE-ID Element 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PE-ID Element n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U (Unknown) bit of thus LDP TLV MUST be set to 1. If the PE-ID TLV is
not understood then it is ignored the receiving device.
F (Forward) MUST be set to 0. Since the LDP mechanism used here is
targeted, the TLV is not forwarded if it is not understood by the
receiving device.
The Type field MUST be set to 0x405 (subject to IANA approval). This
identifies the TLV type as PE-ID TLV.
Length field specifies the total length in octets of the Value in PE-
ID TLV.
PE-ID Element 1 to PE-ID Element n: there are several types of PE-ID
Elements. The PE-ID Element Encoding depends on the type of the PE-ID
Element. A PE-ID Element uniquely identifies a PW Endpoint.
A PE-ID Element value is encoded as 1 octet field that specifies the
element type, 1 octet field that identifies the length in octets of
the element value, and a variable length field that is type dependent
element value.
The PE-ID Element value encoding is:
PE-ID name Type Length Value
FEC-128 specific 0x01 12 octets See below.
FEC-129 specific 0x02 Variable See below.
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The type of PE-ID Element depends on the type of FEC Element used to
provision the respective PW. [RFC4447] defines two types of FEC
elements that may be used for provisioning PWs - Pwid FEC (type 128)
and the Generalized ID (GID) FEC (type 129). The Pwid FEC element
includes a fixed-length 32 bit value called the PWid. The same PWid
value must be configured on the local and remote PE prior to PW
setup. The GID FEC element includes TLV fields for attachment
individual identifiers (AII) that, in conjunction with an attachment
group identifier (AGI), serve as PW endpoint identifiers. The
endpoint identifier on the local PE (denoted as <AGI, source AII or
SAII>) is called the source attachment identifier (SAI) and the
endpoint identifier on the remote PE (denoted as <AGI, target AII or
TAII>) is called the target attachment identifier (TAI). The SAI and
TAI can be distinct values. This is useful for provisioning models
where the local PE (with a particular SAI) does not know and must
somehow learn (e.g. via MP-BGP auto-discovery) of remote TAI values
prior to launching PW setup messages towards the remote PE.
FEC-128 specific PE-ID Element
This sub-type is to be used to identify a PW endpoint only if Pwid
FEC Element is used for signaling the PW. The encoding of this PE-ID
element is as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x01 | Length | PW type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Endpoint Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PW type: The PW Type value from PWid FEC element.
PW ID: The PW ID value from the Pwid FEC element.
Endpoint Address: 32-bit LSR-ID from the LDP-ID used in LDP
signaling Session by a PW endpoint.
FEC-129 specific PE-ID element
This sub-type is to be used to indentify a PW endpoint only if GID
FEC Element is used for signaling the PW. The encoding of this PE-ID
element is as follows:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x02 | Length | PW type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AGI TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PW type: The PW Type value from GID FEC element.
PW ID: The PW ID value from the GID FEC element.
AGI TLV: The AGI from the corresponding GID Element
AII TLV: The AII associated with the PW endpoint.
4.1.2. Application of PE-ID TLV in Optimized MAC Flush
For optimized MAC flush, the PE-ID TLV MAY be sent as an OPTIONAL
parameter in existing LDP Address Withdraw Message with empty MAC
List. The PE-ID TLV carries the unique PW endpoint identifier in a
VPLS as described in section 4.
It is to note that for optimized MAC flush the PE-ID TLV carries
sufficient information for identifying the VPLS instance and the
unique VSI Identifier. For backward compatibility with MAC flush
procedures in [RFC4762] both FEC TLV and PE-ID TLV should be sent in
the MAC flush message. However the inclusion of the FEC-TLV should be
based on what would be the desired effect should the PE-ID not be
understood by the receiver. In cases where the desired action when
the PE-ID is not understood would be to behave as described in
[RFC4762], then the FEC TLV SHOULD be always included. In cases
where the desired action when the PE-ID is not understood is no mac
flushing, then the FEC TLV SHOULD NOT be included. The PE-ID TLV
SHOULD carry the unique VSI identifier in the VPLS instance
(specified in the FEC TLV). The PE-ID TLV SHOULD be placed after the
existing TLVs in MAC Flush message in [RFC4762].
4.1.3. PE-ID TLV Processing Rules
This section describes the processing rules of PE-ID TLV that SHOULD
be followed in the context of MAC flush procedures in an H-VPLS.
When an MTU-s triggers MAC flush after activation of backup spoke PW,
it MAY send the PE-ID TLV that identifies VSI in the formerly active
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PE device. There may be cases where a PE device in full mesh
initiates MAC flush towards the core when it detects a spoke PW
failure. In such a case the PE-ID TLV in MAC flush message MAY
identify its own VSI. Irrespective of whether it is the MTU-s or PE
device that initiates the MAC flush, a PE device receiving the PE-ID
TLV SHOULD follow the same processing rules as described in this
section.
Note that if MS-PW is used in VPLS then a MAC flush message is
processed only at the T-PE nodes since S-PE(s) traversed by the MS-PW
propagate MAC flush messages without any action. In this section, a
PE device signifies only T-PE in MS-PW case unless specified
otherwise.
When a PE device receives a MAC flush with PE-ID TLV, it SHOULD flush
all the MAC addresses learned from the PW that terminates in the
remote VSI identified by the PE-ID element.
If a PE-ID element received in the MAC flush message identifies the
local VSI, it SHOULD flush the MAC addresses learned from its local
spoke PW(s) in the VPLS instance.
If a PE device receives a MAC flush with the PE-ID TLV option and a
valid MAC address list, it SHOULD ignore the option and deal with MAC
addresses explicitly as per [RFC4762].
If a PE device that doesn't support PE-ID TLV receives a MAC flush
message with this option, it MUST ignore the option and follow the
processing rules as per [RFC4762].
4.1.4. Optimized MAC Flush Procedures
This section explains the optimized MAC flush procedure in the
scenario in Figure 1. When the backup PW is activated by MTU-s, it
may send MAC flush message to PE-2 with the FEC TLV and the optional
PE-ID TLV. The PE-ID element carries the VSI identifier in PE-1 for
the VPLS. Upon receipt of the MAC flush message, PE-2 identifies the
VPLS instance that requires MAC flush from the FEC element in the FEC
TLV. From the PE-ID TLV, PE-2 identifies the PW in the VPLS that
terminates in PE-1. PE-2 removes all MAC addresses learned from that
PW. PE-2 relays MAC flush messages with the received PE-ID to all its
peer PE devices. When the message is received at PE-3, it identifies
the PW that terminates in the remote VSI in PE-1. PE-3 removes all
MAC addresses learned on the PW that terminated in PE1. There may be
redundancy scenerios where a PE device in the full mesh may be
required to initiate optimized MAC Address Withdrawal. Figure 3 shows
a redundant H-VPLS topology to protect against failure of MTU-s
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device. Provider RSTP may be used as selection algorithm for active
and backup PWs in order to maintain the connectivity between MTU
devices and PE devices at the edge. It is assumed that PE devices can
detect failure on PWs in either direction through OAM mechanisms such
as VCCV procedures for instance.
MTU-1================PE-1===============PE-3
|| || \ /||
|| Redundancy || \ / ||
|| Provider RSTP || Full-Mesh . ||
|| || / \ ||
|| || / \||
MTU-2----------------PE-2===============PE-4
Backup PW
Figure 3: Redundancy with Provider RSTP
MTU-1, MTU-2, PE-1 and PE-2 participate in provider RSTP. By
configuration in RSTP it is ensured that the PW between MTU-1 and PE-
1 is active and the PW between MTU-2 and PE-2 is blocked (made
backup) at MTU-2 end. When the active PW failure is detected by RSTP,
it activates the PW between MTU-2 and PE-2. When PE-1 detects the
failing PW to MTU-1, it may trigger MAC flush into the full mesh
with PE-ID TLV that carries its own VSI identifier in the VPLS. Other
PE devices in the full mesh that receive the MAC flush message
identify their respective PWs terminating on PE-1 and flush all the
MAC addresses learned from it.
By default, MTU-2 should still trigger MAC flush as currently defined
in [RFC4762] after the backup PW is made active by RSTP. Mechanisms
to prevent two copies of MAC withdraws to be sent in such scenarios
is out of scope of this document.
[RFC4762] describes multi-domain VPLS service where fully meshed VPLS
networks (domains) are connected together by a single spoke PW per
VPLS service between the VPLS "border" PE devices. To provide
redundancy against failure of the inter-domain spoke, full mesh of
inter-domain spokes can be setup between border PE devices and
provider RSTP may be used for selection of the active inter-domain
spoke. In case of inter-domain spoke PW failure, PE initiated MAC
withdrawal may be used for optimized MAC flushing within individual
domains.
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4.2. LDP MAC Withdraw Extensions for PBB-VPLS
The use of Address Withdraw message with MAC List TLV is proposed in
[RFC4762] as a way to expedite removal of MAC addresses as the result
of a topology change (e.g. failure of a primary link of a VPLS PE and
implicitly the activation of an alternate link in a dual-homing use
case). These existing procedures apply individually to B-VPLS and I-
component domains.
When it comes to reflecting topology changes in access networks
connected to I-component across the B-VPLS domain certain additions
should be considered as described below.
MAC Switching in PBB is based on the mapping of Customer MACs (CMACs)
to Backbone MAC(s) (BMACs). A topology change in the access (I-
domain) should just invoke the flushing of CMAC entries in PBB PEs'
FIB(s) associated with the I-component(s) impacted by the failure.
There is a need to indicate the PBB PE (BMAC source) that originated
the MAC Flush message to selectively flush only the MACs that are
affected.
These goals can be achieved by adding a new MAC Flush Parameters TLV
in the LDP Address Withdraw message to indicate the particular
domain(s) requiring MAC flush. On the other end, the receiving PEs
may use the information from the new TLV to flush only the related
FIB entry/entries in the I-component instance(s).
4.2.1. MAC Flush Parameters TLV format
The MAC Flush Parameters TLV is described as below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|1| MAC Flush Params TLV(TBD) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Sub-TLV Type | Sub-TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLV Variable Length Value |
| " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The U and F bits are set to forward if unknown so that potential
intermediate VPLS PEs unaware of the new TLV can just propagate it
transparently. The MAC Flush Parameters TLV type is to be assigned by
IANA. The encoding of the TLV follows the standard LDP TLV encoding
in [RFC5036].
The TLV value field contains an one byte Flag field used as described
below. Further the TLV value may carry one or more sub-TLVs. Any sub-
TLV definition to the above TLV MUST address the actions in
combination with other existing sub-TLVs.
The detailed format for the Flags bit vector is described below:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|C|N| MBZ | (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+
1 Byte Flag field is mandatory. The following flags are defined :
C flag, used to indicate the context of the PBB-VPLS component in
which MAC flush is required. For PBB-VPLS there are two contexts of
MAC flushing - The Backbone VPLS (B-component VPLS) and Customer
VPLS (I-component VPLS). C flag MUST be ZERO (C=0) when a MAC Flush
for the B-VPLS is required. C flag MUST be set (C=1) when the MAC
Flush for I-VPLS is required.
N flag, used to indicate whether a positive (N=0, Flush-all-but-
mine) or negative (N=1 Flush-all-from-me) MAC Flush is required.
The source (mine/me) is defined either as the PW associated with
the LDP session on which the LDP MAC Withdraw was received or with
the BMAC(s) listed in the BMAC Sub-TLV.
MBZ flags, the rest of the flags should be set to zero on
transmission and ignored on reception.
The following sub-TLVs MUST be included in the MAC Flush Parameters
TLV if the C-flag is set to 1:
- PBB BMAC List sub-TLV:
Type: 0x01
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Length: value length in octets. At least one BMAC address must be
present in the list.
Value: one or a list of 48 bits BMAC addresses. These are the source
BMAC addresses associated with the B-VPLS instance that originated
the MAC Withdraw message. It will be used to identify the CMAC(s)
mapped to the BMAC(s) listed in the sub-TLV.
- PBB ISID List sub-TLV:
Type: 0x02,
Length: value length in octets. Zero indicates an empty ISID list. An
empty ISID list means that the flush applies to all the ISIDs mapped
to the B-VPLS indicated by the FEC TLV.
Value: one or a list of 24 bits ISIDs that represent the I-component
FIB(s) where the MAC Flush needs to take place.
4.2.2. MAC Flush Parameters TLV Processing Rules
The following steps describe the details of the processing for the
related LDP Address Withdraw message:
. The LDP MAC Withdraw Message, including the MAC Flush Parameters
TLV is initiated by the PBB PE(s) experiencing a Topology Change
event in one or multiple customer I-component(s).
o The flags are set accordingly to indicate the type of MAC
Flush required for this event: N=0 (Flush-all-but-mine),
C=1 (Flush only CMAC FIBs).
o The PBB Sub-TLVs (BMAC and ISID Lists) are included
according to the context of topology change.
. On reception of the LDP Address Withdrawal message, the B-VPLS
instances corresponding to the FEC TLV in the message must
interpret the content of MAC Flush Parameters TLV. If the C-bit is
set to 1 then Backbone Core Bridges (BCB) in the PBB-VPLS SHOULD
NOT flush their BMAC FIBs. The B-VPLS control plane SHOULD
propagate the MAC Flush following the split-horizon grouping and
the established B-VPLS topology.
. The usage and processing rules of MAC Flush Parameters TLV in the
context of Backbone Edge Bridges (BEB) is as follows:
.
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o The PBB ISID List is used to determine the particular ISID
FIBs (I-VPLS) that need to be flushed. If the ISID List is
empty then all the ISID FIBs associated with the receiving
B-VPLS SHOULD be flushed.
o The PBB BMAC List is used to identify from the ISID FIBs
in the previous step to selectively flush BMAC to CMAC
associations depending on the N flag specified below.
. Next, depending on the N flag value the following actions apply:
o N=0, all the CMACs in the selected ISID FIBs SHOULD be
flushed with the exception of the resulted CMAC list from
the BMAC List mentioned in the message. ("Flush all but the
CMACs associated with the BMAC(s) in the BMAC List Sub-TLV
from the FIBs associated with the ISID list").
o N=1, the resulted CMAC list SHOULD be flushed ("Flush all
the CMACs associated with the BMAC(s) in the BMAC List Sub-
TLV from the FIBs associated with the ISID list").
4.2.3 Applicability of MAC Flush Parameters TLV
If MAC Flush Parameters TLV is received by a BEB in a PBB-VPLS
that does not understand the TLV then it may result in undesirable
MAC flushing action. It is RECOMMENDED that all PE devices
participating in PBB-VPLS support MAC Flush Parameters TLV.
The MAC Flush Parameters TLV is also applicable to regular VPLS
context as well. To achieve negative MAC Flush (flush-all-from-me) in
regular VPLS context, the MAC Flush Parameters TLV SHOULD be encoded
with C=0 and N = 1 without inclusion of any Sub-TLVs. Negative MAC
flush is highly desirable in scenarios when VPLS access redundancy is
provided by Ethernet Ring Protection as specified in ITU-T G.8032
specification etc.
5. Security Considerations
Control plane aspects:
- LDP security (authentication) methods as described in [RFC5036] is
applicable here. Further this document implements security
considerations as in [RFC4447] and [RFC4762].
Data plane aspects:
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- This specification does not have any impact on the VPLS forwarding
plane.
6. IANA Considerations
The Type field in PE-ID TLV is defined as 0x405 and is subject to
IANA approval.
The Type field in MAC Flush Parameters TLV is defined as 0x406 and is
subject to IANA approval.
7. Acknowledgments
The authors would like to thank the following people who have
provided valuable comments and feedback on the topics discussed in
this document: Marc Lasserre, Dimitri Papadimitriou, Jorge Rabadan,
Prashanth Ishwar, Vipin Jain, John Rigby, Ali Sajassi, Wim
Henderickx, Jorge Rabadan and Maarten Vissers.
8. References
8.1. Normative References
[RFC4762] Lasserre, M. and Kompella, V. (Editors), "Virtual Private
LAN Service (VPLS) Using Label Distribution Protocol (LDP)
Signaling", RFC 4762, January 2007.
[RFC5036] Andersson, L., et al. "LDP Specification", RFC5036, October
2007.
[RFC4447] Martini. and et al., "Pseudowire Setup and Maintenance
Using Label Distribution Protocol (LDP)", RFC 4447, April
2006.
8.2. Informative References
[PBB-VPLS Model] F. Balus, et Al. "Extensions to VPLS PE model for
Provider Backbone Bridging", draft-ietf-l2vpn-pbb-vpls-pe-
model-00.txt, May 2009 (work in progress)
[RFC4664] Andersson, L., et al. "Framework for Layer 2 Virtual
Private Networks (L2VPNs)", RFC 4664, September 2006.
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[802.1w] "IEEE Standard for Local and metropolitan area networks.
Common specifications Part 3: Media Access Control (MAC)
Bridges. Amendment 2: Rapid Reconfiguration", IEEE Std
802.1w-2001.
Author's Addresses
Pranjal Kumar Dutta
Alcatel-Lucent
701 E Middlefield Road,
Mountain View, CA 94043
USA
Email: pranjal.dutta@alcatel-lucent.com
Florin Balus
Alcatel-Lucent
701 E. Middlefield Road
Mountain View, CA, USA 94043
Email: florin.balus@alcatel-lucent.com
Geraldine Calvignac
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
France
Email: geraldine.calvignac@orange-ftgroup.com
Olen Stokes
Extreme Networks
PO Box 14129
RTP, NC 27709
USA
Email: ostokes@extremenetworks.com
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