LDP Extensions for Optimized MAC Address Withdrawal in H-VPLS
draft-ietf-l2vpn-vpls-ldp-mac-opt-07
The information below is for an old version of the document.
| Document | Type |
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|---|---|---|---|
| Authors | Pranjal Dutta , Florin Balus , Olen Stokes , Geraldine Calvignac | ||
| Last updated | 2012-09-09 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-l2vpn-vpls-ldp-mac-opt-07
Network Working Group P. Dutta
Internet-Draft F. Balus
Intended status: Standards Track Alcatel-Lucent
Expires: March 13, 2013 O. Stokes
Extreme Networks
G. Calvinac
France Telecom
September 09, 2012
LDP Extensions for Optimized MAC Address Withdrawal in H-VPLS
draft-ietf-l2vpn-vpls-ldp-mac-opt-07
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 [I-D.ietf-l2vpn-pbb-vpls-pe-model] .
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 13, 2013.
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. MAC Flush on activation of backup spoke PW . . . . . . . . 5
2.1.1. PE-rs initiated MAC Flush . . . . . . . . . . . . . . 5
2.1.2. MTU-s initiatied MAC flush . . . . . . . . . . . . . . 6
2.2. MAC Flush on failure . . . . . . . . . . . . . . . . . . . 7
2.3. MAC Flush in PBB-VPLS . . . . . . . . . . . . . . . . . . 7
3. Problem Description . . . . . . . . . . . . . . . . . . . . . 7
3.1. MAC Flush Optimization in VPLS Resiliency . . . . . . . . 7
3.1.1. MAC Flush Optimization for regular H-VPLS . . . . . . 8
3.1.2. MAC Flush Optimization for native Ethernet access . . 9
3.2. Black holing issue in PBB-VPLS . . . . . . . . . . . . . . 10
4. Solution Description . . . . . . . . . . . . . . . . . . . . . 11
4.1. MAC Flush Optimization for VPLS Resiliency . . . . . . . . 11
4.1.1. MAC Flush Parameters TLV . . . . . . . . . . . . . . . 11
4.1.2. Application of MAC Flush TLV in Optimized MAC Flush . 13
4.1.3. MAC Flush TLV Processing Rules for Regular VPLS . . . 13
4.1.4. Optimized MAC Flush Procedures . . . . . . . . . . . . 14
4.2. LDP MAC Flush Extensions for PBB-VPLS . . . . . . . . . . 15
4.2.1. MAC Flush TLV Processing Rules for PBB-VPLS . . . . . 16
4.2.2. Applicability of MAC Flush Parameters TLV . . . . . . 18
5. Operational Considerations . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 19
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Terminology
This document uses the terminology defined in
[I-D.ietf-l2vpn-pbb-vpls-pe-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-rs devices offering the VPLS [RFC4762].
The terms "Spoke Node" and "MTU-s" in H-VPLS are used
interchangeably.
"Spoke PW" means the PW (Pseudowire) that provides connectivity
between MTU-s and PE-rs nodes.
"Mesh PW" means the PW that provides connectivity between PE-rs nodes
in a VPLS full mesh core.
"MAC Flush Message" means LDP Address Withdraw Message with MAC List
TLV.
MAC Flush Message in the "context of a PW" means the Message that has
been received over the LDP session that is used to set up the PW used
to provide connectivity in VPLS. The MAC Flush Message carries the
context of the PW in terms on FEC TLV associated with the PW
[RFC4762][RFC4447].
In general, "MAC Flush" means the method of initiating and processing
of MAC Flush Messages across a VPLS instance.
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]. Throughout this document this
configuration is referred to as "regular" H-VPLS.
[I-D.ietf-l2vpn-pbb-vpls-pe-model] describes how Provider Backbone
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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-MAC (Customer MAC) Addresses 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. Note that the H-VPLS topology
in [RFC4762] describes two tier hierarchy to VPLS as the basic
building block of H-VPLS, but it is possible to have multi-tier
hierarchy in an H-VPLS.
The figure 1. described below is taken from [RFC4762] that describes
dual-homing in H-VPLS.
PE2-rs
+--------+
| |
| -- |
| / \ |
CE-1 | \S / |
\ | -- |
\ +--------+
\ MTU-s PE1-rs / |
+--------+ +--------+ / |
| | | | / |
| -- | Primary PW | -- |---/ |
| / \ |- - - - - - - - - - - | / \ | |
| \S / | | \S / | |
| -- | | -- |---\ |
+--------+ +--------+ \ |
/ \ \ |
/ \ +--------+
/ \ | |
CE-2 \ | -- |
\ Secondary PW | / \ |
- - - - - - - - - - - - - - - - - | \S / |
| -- |
+--------+
PE3-rs
Figure 1: An example of a dual-homed MTU-s
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
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spoke PW or primary PE device. There could be multiple methods of
dual homing in H-VPLS that are not described in [RFC4762]. For
example, note the following statement from section 10.2.1 in .
"How a spoke is designated primary or secondary is outside the scope
of this document. For example, a spanning tree instance running
between only the MTU-s and the two PE-rs nodes is one possible
method. Another method could be configuration".
This document intends to clarify several H-VPLS dual-homing models
that are deployed in practice and various use cases of LDP based MAC
flush in such models.
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. This is accomplished by sending an LDP Address
Withdraw Message with the list of MAC addresses to be removed to all
other PEs over the corresponding LDP sessions [RFC4762].
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. The
solutions describes in this document are applicable only to LDP
Address Withdraw Message with empty MAC List.
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.
Throughout this document we use the terminology "Positive" MAC Flush
or "Flush-all-but-mine" for this type of MAC Flush Message and its
actions.
2.1. MAC Flush on activation of backup spoke PW
This section describes scenerios where MAC Flush withdrawal is
initiated on activation of backup PW in H-VPLS.
2.1.1. PE-rs initiated MAC Flush
[RFC4762] specifies that on failure of the primary PW, it is the
PE3-rs (Figure 1) that initiates MAC flush towards the core. However
note that PE3-rs can initiate MAC Flush only when PE3-rs is dual
homing "aware" - that is, there is some redundancy management
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protocol running between MTU-s and its host PE-rs devices. The scope
of this document is not specific to any dual homing protocols. One
example could be BGP based multi-homing in LDP based VPLS that uses
the procedures defined in [I-D.ietf-l2vpn-vpls-multihoming]. In this
method of dual-homing, PE3-rs would neither forward any traffic to
MTU-s neither would receive any traffic from MTU-s while PE1-rs is
acting a primary (or designated forwarder).
2.1.2. MTU-s initiatied MAC flush
When dual homing is achieved by manual configuration in MTU-S, the
hosting PE-rs devices are dual homing "agnostic" and PE3-rs can not
initiate MAC Flush message. PE3-rs can send or receive traffic over
the backup PW since the dual-homing control is with MTU-s only. When
the backup PW is made active by the MTU-s, it triggers MAC Flush
Message. The message is sent over the LDP session associated with
the newly activated PW. On receiving the MAC Flush Message from
MTU-s, PE3-rs (PE-rs device with now-active PW) would flush all the
MAC addresses it has learned except the ones learned over the newly
activated spoke PW. PE3-rs further forwards the MAC Flush Message to
all other PE devices in the core. Note that forced switchover to
backup PW can be also performed at MTU-s administratively due to
maintenance activities on the "erstwhile" primary spoke PW.
MTU-s initiated 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.
The MAC Flush forwarding rules in LDP control plane strictly follow
the "split-horizon" forwarding rules in H-VPLS data plane (Refer to
section 4.4 in [RFC4762]). So a MAC Flush is forwarded in the
context of mesh PW(s) when it is received in the context of a spoke
PW. When a PE-rs node receives a MAC Flush in the context of a mesh
PW then it is not forwarded to other mesh PWs.
Irrespective of whether a MAC Flush is initiated by a PE-rs or MTU-s,
when a PE-rs 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 that it flushes only the set of
MAC addresses that require relearning when topology changes in
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H-VPLS.
2.2. MAC Flush on failure
This is a method of MAC Flush introduced by this document. In this
model of dual-homing the MAC Flush is initiated by PE1-rs (Figure 1)
on detection of failure of the primary spoke PW and is sent to all
participating PE-rs devices in the VPLS full-mesh. It is needless to
say that PE1-rs can initiate MAC flush only if PE1-rs is dual homing
aware. The dual-homing protocols for this scenerio are outside the
scope of this document. For example, the case of PE1-rs initiated
MAC flush on failure may arise when the dual-homing segment is native
ethernet as opposed to spoke PWs. In this case the PE-rs devices
that receives the MAC flush from PE1-rs are required to flush all the
MAC addresses learned over the PW connected to PE1-rs. This cannot
be achieved with the MAC Flush Mechanism defined in [RFC4762]. This
document describes extensions to MAC Flush procedures defined in
[RFC4762] in order to implement MAC Flush on Failure. We use the
term "negative" MAC flush or "Flush-all-from-me" for this kind of
flushing action as opposed to "positive" MAC Flush action in
[RFC4762]
2.3. MAC Flush in PBB-VPLS
[I-D.ietf-l2vpn-pbb-vpls-pe-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 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 PE-rs devices. This document describes
extensions to LDP MAC Flush procedures described in [RFC4762]
required to build desirable capabilities to PBB-VPLS solution.
The solution proposed in this document is generic and is applicable
when MS-PWs are used in interconnecting PE devices in H-VPLS. There
could be other H-VPLS models not defined in this document where the
solution may be applicable.
3. Problem Description
This document describes the problems in detail with respective to
various MAC flush actions described in section 2.
3.1. MAC Flush Optimization in VPLS Resiliency
This section decribes the optimizations required in MAC flush
procedures when H-VPLS resiliency is provided by primary and backup
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spoke PWs.
3.1.1. MAC Flush Optimization for regular H-VPLS
Figure 2. describes a dual-homed H-VPLS scenario for a VPLS instance
where the problem with the existing MAC flush method (section 1.1) in
is explained. [RFC4762]
PE1-rs PE3-rs
+--------+ +--------+
| | | |
| -- | | -- |
Customer Site 1 | / \ |------------------| / \ |->Z
X->CE-1 /-----| \ s/ | | \S / |
\ primary spoke PW | -- | /------| -- |
\ / +--------+ / +--------+
\ (MTU-s)/ | \ / |
+--------+/ | \ / |
| | | \ / |
| -- | | \ / |
| / \ | | H-VPLS Full Mesh Core|
| \S / | | / \ |
| -- | | / \ |
/+--------+\ | / \ |
/ backup spoke PW | / \ |
/ \ +--------+ \--------+--------+
Y->CE-2 \ | | | |
Customer Site 2 \------| -- | | -- |
| / \ |------------------| / \ |->
| \s / | | \S / |
| -- | | -- |
+--------+ +--------+
PE2-rs PE4-rs
Figure 2: Dual homed MTU-s in two tier hierarchy H-VPLS
In Figure 2, the MTU-s is dual-homed to PE1-rs and PE2-rs. Only the
primary spoke PW is active at MTU-s, thus PE1-rs is acting as the
active device (designated forwarder) 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 PE1-rs over the primary spoke PW.
Let's say X represets a set of such MAC addresses ocated behind CE-1.
As packet flows from X to Z, PE2-rs, PE3-rs and PE4-rs learn about X
on their respective mesh PWs terminating at PE1-rs. When MTU-s
switches to the backup spoke PW and activates it, PE2-rs becomes the
active device (designated forwarder) 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 spoke PW to PE2-rs. Traffic destinated from PE2-rs,
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PE3-rs and PE4-rs to X will be blackholed till MAC address ageing
timer expires (default is 5 minutes) or a packet flows from X to Z
through PE2-rs. To avoid traffic blackholing the MAC addresses that
have been learned in the upstream VPLS full-mesh through PE1-rs,
those must be relearned or removed from the MAC FIBs in the VSIs at
PE2-rs, PE3-rs and PE4-rs. If PE1-rs and PE2-rs are dual-homing
agnostic then on activation of the standby PW from MTU-s, a MAC flush
message will be sent by MTU-s to PE2-rs that will flush all the MAC
addresses learned in the VPLS from all the other PWs but the PW
connected to MTU-s.
PE2-rs further relays MAC flush messages to all other PE-rs devices
in the full mesh. Same processing rule applies at all those PE-rs
devices: all the MAC addresses are flushed but the ones learned on
the PW conneced to to PE2-rs. For example, at PE3-rs all of the MAC
addresses learned from the PWs connected to PE1-rs and PE4-rs are
flushed and relearned subsequently. Before the relearning happens
flooding of unknown destination MAC addresses takes place throughout
the network. As the number of PE-rs 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. An optimization is required that will flush
only the MAC addresses learned from the respective PWs between PE1-rs
and other PE devices in the full-mesh in order to minimize the
relearning and flooding in the network. In the above case, only the
MAC addresses in set X and Y needs to be flushed across the core.
The same case is applicable when PE1-rs and PE2-rs are dual homing
aware and participates in a designated forwarder election. When
PE2-rs becomes the active device for MTU-s then PE2-rs may initiate
MAC flush towards the core. The receiving action of the MAC Flush in
other PE-rs devices is same as in MTU-s initiated MAC Flush.
3.1.2. MAC Flush Optimization for native Ethernet access
The analysis in section 2.1.1 applies also to the native Ethernet
access into a VPLS. In such a scenerio one active and one or more
standby endpoints terminate into two or more VPLS or H-VPLS PE-rs
devices. Example of these kind of access are ITU-T G.8032 access
rings or any proprietary multi-chassis LAG emulations. Upon failure
of the active native Ethernet endpoint on PE1-rs, an optimized MAC
flush is required to be initiated by PE1-rs to ensure that on PE2-rs,
PE3-rs and PE4-rs only the MAC addresses learned from the respective
PWs connected to PE1-rs are being flushed.
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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 to support 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 3 describes the case of a CE
device (node A) dual-homed to two I-component instances located on
two PBB-VPLS PEs (PE1-rs and PE2-rs).
IP/MPLS Core
+--------------+
|PE2-rs |
+----+ |
|PBB | +-+ |
|VPLS|---|P| |
S/+----+ /+-+\ |PE3-rs
/ +----+ / \+----+
+---+/ |PBB |/ +-+ |PBB | +---+
CMAC X--|CE |---|VPLS|---|P|--|VPLS|---|CE |--CMAC Y
+---+ A +----+ +-+ +----+ +---+
A |PE1-rs | B
| |
+--------------+
Figure 3: PBB Black holing Issue - CE Dual-Homing use case
The link between PE1-rs and CE-A is active (marked with A) while the
link between CE-A and PE2-rs 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 B-VPLS
instances on PE1-rs are associated with "Backbone" MAC (BMAC) B1 and
PE2-rs with BMAC B2.
As the packets flow from CMAC X to CMAC Y through PE1-rs with BMAC
B1, the remote PE-rs devices participating in the I-VPLS (for
example, PE3-rs) will learn the CMAC X associated with BMAC B1 on
PE1-rs. Under failure of the link between CE-A and PE1-rs and on
activation of link to PE2-rs, the remote PE-rs devices (for example,
PE3-rs) 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 the BMAC associated with the
PE-rs in the B-VPLS domain where the failure occurred. This will
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automatically flush the CMAC to BMAC association in the remote PE-rs
devices. 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 CMAC to BMAC associations in the remote PBB-VPLS capable PE-rs
devices. As there are no I-VPLS 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
This section describes the solution for the requirements described in
section 3.
4.1. MAC Flush Optimization for VPLS Resiliency
The basic principle of the optimized MAC flush mechanism is explained
with reference to Figure 2. The optimization is achieved by
initiating MAC Flush on failure as described in section 1.2
PE1-rs would initiate MAC Flush towards the core on detection of
failure of primary spoke PW between MTU-S and PE1-rs (or status
change from active to standby [I-D.ietf-pwe3-redundancy] ). This
method is referred as "MAC Flush on Failure" throughout this
document. The MAC Flush message would indicate to receiving PE-rs
devices to flush all MACs learned over the PW in the context of the
VPLS over which the MAC flush message is received. Each PE-rs device
in the full mesh that receives the message identifies the VPLS
instance and its respective PW that terminates in PE1-rs from the FEC
TLV received in the message. Thus the PE-rs device flushes only the
MAC addresses learned from that PW connected to PE1-rs, minimizing
the required relearning and the flooding throughout the VPLS domain.
This section defines a generic MAC Flush Parameters TLV for LDP
[RFC5036]. Through out this document the MAC Flush Parameters TLV is
referred as MAC Flush TLV. A MAC Flush TLV carries information on
the desired action at the PE-rs device receiving the message and is
used for optimized MAC flushing in VPLS. The MAC Flush TLV can also
be used for [RFC4762] style of MAC Flush as explained in section 2.1.
4.1.1. MAC Flush Parameters TLV
The MAC Flush Parameters TLV is described as below:
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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|1| MAC Flush Params TLV(TBD) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Sub-TLV Type | Sub-TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLV Variable Length Value |
| " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The U and F bits are set to forward if unknown so that potential
intermediate VPLS PE-rs devices 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 a 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. In the regular H-VPLS case the C flag must
be ZERO (C=0) to indicate the flush applies to the current VPLS
context.
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. For the optimized MAC Flush
procedure described in this section the flag must be set (N=1).
Detailed usage in the context of PBB-VPLS is explained in section
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3.2.
MBZ flags, the rest of the flags should be set to zero on
transmission and ignored on reception.
The MAC Flush TLV SHOULD be placed after the existing TLVs in MAC
Flush message in [RFC4762].
4.1.2. Application of MAC Flush TLV in Optimized MAC Flush
For optimized MAC flush, the MAC Flush TLV MAY be sent as in existing
LDP Address Withdraw Message with empty MAC List but from the core
PE-rs on detection of failure of its local/primary spoke PW. The N
bit in TLV MUST be set to 1 to indicate Flush-all-from-me. If the
optimized MAC Flush procedure is used in a Backbone VPLS or regular
VPLS/H-VPLS context the C bit must be ZERO (C=0). If it is used in
an I-VPLS context the C bit must be set (C= 1). See section 3.2 for
details of its usage in PBB-VPLS context.
Note that if MAC Flush TLV is not understood by a receiver (i.e. a
legacy PE-rs then it may result in undesired action. For example if
a MAC Flush Parameters TLV is received with N=1 and receiver does not
understand that TLV then it would result in flushing of all MACs
learned in the VSI except the ones learned over the PW (positive MAC
Flushing action).
To emulate the MAC flush initiation procedures defined in [RFC4762],
MTU-s or PE2-rs MAY send MAC Flush TLV as an OPTIONAL TLV in the MAC
Flush Message with N = 0. This would result in same flushing action
at receiving PE-rs devices.
4.1.3. MAC Flush TLV Processing Rules for Regular VPLS
This section describes the processing rules of MAC Flush TLV that
SHOULD be followed in the context of MAC flush procedures in VPLS.
For optimized MAC Flush a multi-homing PE-rs initiates MAC flush
message towards the other related VPLS PE-rs devices when it detects
a transition (failure or to standby) in its active spoke PW. In such
case the MAC Flush TLV MUST be sent with N= 1. A PE-rs device
receiving the MAC Flush 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-rsdevice signifies only T-PE in MS-PW case unless specified
otherwise.
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When a PE-rs device receives a MAC Flush TLV with N = 1, it SHOULD
flush all the MAC addresses learned from the PW in the VPLS in the
context on which the MAC Flush message is received.
If a MAC Flush TLV is received with N = 0 in the MAC flush message
then the receiving PE-rs SHOULD flush the MAC addresses learned from
all PWs in the VPLS instance except the ones learned over the PW on
which the message is received.
If a PE-rs device receives a MAC flush with the MAC Flush 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-rs device that doesn't support MAC Flush TLV receives a MAC
flush message with this option, it MUST ignore the option and follow
the processing rules as per [RFC4762]. However if MAC Flush
Parameters TLV was sent with N = 1 then it may result in wrong
flushing action (Positive MAC Flush).
4.1.4. Optimized MAC Flush Procedures
This section explains the optimized MAC flush procedure in the
scenario in Figure 2. When the primary spoke PW transition (failure
or standby transition) is detected by PE1-rs, it may send MAC flush
messages to PE2-rs, PE3-rs and PE4-rs with MAC Flush TLV and N = 1.
Upon receipt of the MAC flush message, PE2-rs identifies the VPLS
instance that requires MAC flush from the FEC element in the FEC TLV.
On receiving N=1, PE-2 removes all MAC addresses learned from that PW
over which the message is received. Same action is followed by
PE3-rs and PE4-rs.
Figure 4 shows another redundant H-VPLS topology to protect against
failure of MTU-s 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-rs devices at the edge. It
is assumed that PE-rs devices can detect failure on PWs in either
direction through OAM mechanisms such as VCCV procedures for
instance.
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MTU-1================PE-1===============PE-3
|| || \ /||
|| Redundancy || \ / ||
|| Provider RSTP || Full-Mesh . ||
|| || / \ ||
|| || / \||
MTU-2----------------PE-2===============PE-4
Backup PW
Figure 4: Redundancy with Provider RSTP
MTU-1, MTU-2, PE1-rs and PE2-rs participate in provider RSTP. By
configuration in RSTP it is ensured that the PW between MTU-1 and
PE1-rs is active and the PW between MTU-2 and PE2-rs 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 PE2-rs. When PE1-rs
detects the failing PW to MTU-1, it may trigger MAC flush into the
full mesh with MAC Flush TLV that carries N=1. Other PE-rs devices
in the full mesh that receive the MAC flush message identify their
respective PWs terminating on PE1-rs and flush all the MAC addresses
learned from it.
[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-rs devices. To provide
redundancy against failure of the inter-domain spoke, full mesh of
inter-domain spokes can be setup between border PE-rs devices and
provider RSTP may be used for selection of the active inter-domain
spoke. In case of inter-domain spoke PW failure, PE-rs initiated MAC
withdrawal may be used for optimized MAC flushing within individual
domains.
Further, the procedures are applicable with any native Ethernet
access topologies multi-homed to two or more VPLS PE-rs devices. The
text in section 3.1 applies for the native Ethernet case where
active/standby PWs are replaced with the active/standby Ethernet
endpoints. An optimized MAC Flush message can be generated by the
VPLS PE-rs that detects the failure in the primary Ethernet access.
4.2. LDP MAC Flush 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-rs
device 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.
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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 including the 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).
At least one of 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
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.
4.2.1. MAC Flush TLV Processing Rules for PBB-VPLS
The following steps describe the details of the processing rules for
MAC Flush TLV in the context of PBB-VPLS:
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- The MAC Flush Message 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).
- 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).
- The PBB Sub-TLVs (BMAC and ISID Lists) are included according to
the context of topology change.
- On reception of the MAC Flush 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:
- The PBB ISID List is used to determine the particular ISID FIBs
(I-VPLS) that need to be considered for flushing action. If the PBB
ISID List sub-tlv is not included in a received message then all the
ISID FIBs associated with the receiving B-VPLS SHOULD be considered
fo flushing action.
- 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. If PBB BMAC List Sub-TLV is
not included in a received message then all BMAC to CMAC association
in all ISID FIBs (I-VPLS) as specified by the ISID List are
considered for required flushing action, again depending on the N
flag specified below.
- Next, depending on the N flag value the following actions apply:
- 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").
- N=1, all the resulted CMACs 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").
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4.2.2. 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-rs devices
participating in PBB-VPLS support MAC Flush Parameters TLV.
The MAC Flush Parameters TLV is also applicable to regular VPLS
context as well as explained in section 3.1 . 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. Operational Considerations
As mentioned before, if MAC Flush Parameters TLV is not understood by
a receiver then it may result in undesired flushing action. An LDP
based capability negotiation mechanism may be defined to negotiate
support of various MAC Flushing capability between PE-rs devices in a
VPLS instance. This is a subject of future study.
In a VPLS instance it is possible that some PE-s devices does not
support the solutions defined in this document. From operational
standpoint, it is RECOMMENDED that implementations of the solution
provide administrative control to selectively desired MAC Flushing
action towards a PE-rs device in the VPLS. Thus in the topology
figure 2. it is possible that PE1-rs would initiate optimized MAC
Flush torwards the PE-rs devices that supports the solution , whereas
PE2-rs would initiate [RFC4762] style of MAC Flush towards the PE-rs
devices that does not support the optimized solution.
6. IANA Considerations
This document requests code point for following LDP TLV:
- MAC Flush Parameters TLV.
7. Security Considerations
Control plane aspects:
- LDP security (authentication) methods as described in [RFC5036] is
applicable here. Further this document implements security
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considerations as in [RFC4447] and [RFC4762].
Data plane aspects:
- This specification does not have any impact on the VPLS forwarding
plane.
8. Contributing Authors
The authors would like to thank Marc Lasserre and Don Fedyk who made
a major contribution to the deveopment of this document.
Marc Lasserre
Alcatel-Lucent
Email: marc.lasserre@alcatel-lucent.com
Don Fedyk
Alcatel-Lucent
Groton, MA 01450 USA
Email: Donald.Fedyk@alcatel-lucent.com
9. Acknowledgements
The authors would like to thank the following people who have
provided valuable comments and feedback on the topics discussed in
this document: Dimitri Papadimitriou, Jorge Rabadan, Prashanth
Ishwar, Vipin Jain, John Rigby, Ali Sajassi, Wim Henderickx, Paul
Kwok, Jorge Rabadan, Maarten Vissers, Daniel Cohn, Nabil Bitar and
Giles Heron.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
Heron, "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", RFC 4447, April 2006.
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[RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service
(VPLS) Using Label Distribution Protocol (LDP) Signaling",
RFC 4762, January 2007.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
10.2. Informative References
[I-D.ietf-l2vpn-pbb-vpls-pe-model]
Balus, F., Bocci, M., Sajassi, A., Bitar, N., and R.
Zhang, "Extensions to VPLS PE model for Provider Backbone
Bridging", draft-ietf-l2vpn-pbb-vpls-pe-model-05 (work in
progress), August 2012.
[I-D.ietf-l2vpn-vpls-multihoming]
Kothari, B., Kompella, K., Henderickx, W., Balus, F., and
J. Uttaro, "BGP based Multi-homing in Virtual Private LAN
Service", draft-ietf-l2vpn-vpls-multihoming-03 (work in
progress), July 2011.
[I-D.ietf-pwe3-redundancy]
Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
Redundancy", draft-ietf-pwe3-redundancy-09 (work in
progress), June 2012.
[RFC4664] Andersson, L. and E. Rosen, "Framework for Layer 2 Virtual
Private Networks (L2VPNs)", RFC 4664, September 2006.
[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.
[G.8032] "Ethernet ring protection switching", ITU-T G.8032.
Authors' Addresses
Pranjal Kumar Dutta
Alcatel-Lucent
701 E Middlefield Road
Mountain View, California 94043
USA
Email: pranjal.dutta@alcatel-lucent.com
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Florin Balus
Alcatel-Lucent
701 E Middlefield Road
Mountain View, California 94043
USA
Email: florin.balus@alcatel-lucent.com
Olen Stokes
Extreme Networks
PO Box 14129, RTP
Raleigh, North Carolina 27709
USA
Email: ostokes@extremenetworks.com
Geraldine Calvinac
France Telecom
2, avenue Pierre-Marzin
Lannion Cedex, 22307
France
Email: geraldine.calvignac@orange-ftgroup.com
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