Networking Working Group R. Chen
Internet-Draft Y. Wang
Intended status: Standards Track ZTE Corporation
Expires: September 15, 2011 L. Guo
China Telecom
March 14, 2011
LDP Extensions for Optimized MAC Address Withdrawal in VPLS model 3
supporting Qualified learning
draft-chen-l2vpn-vpls-mac-opt-qualified-01
Abstract
This draft defines a method for optimized MAC Address Withdrawal in
VPLS model 3 ([RFC4664]) supporting qualified learning ([RFC4762]).
Some extensions are made based on the MAC Address Withdrawal
procedures defined in [RFC4762] and
[I-D.ietf-l2vpn-vpls-ldp-mac-opt], in order to enable a PE to remove
only the MAC addresses, which belong to MAC address space affected by
topology change.
Status of this Memo
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This Internet-Draft will expire on September 15, 2011.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Problem Description . . . . . . . . . . . . . . . . . . . . . . 5
4. Optimized MAC Flush Mechanism . . . . . . . . . . . . . . . . . 6
4.1. MAC Address Space TLV . . . . . . . . . . . . . . . . . . . 6
4.2. MAC Address Space TLV Processing Rules . . . . . . . . . . 7
4.3. Optimized MAC Flush Procedures . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
7. Normative references . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
There are operators deploying VPLS with qualified learning mode
[RFC4762], so as to reduce the number of VPLS instance. By using
VLAN within VPLS and qualified learning mode to separate customer
internally, current defined VPLS MAC address withdraw mechanism will
flush MAC addresses VLAN space which are not affected due to topology
change.
[RFC4762] defines a basic MAC Address Withdrawal mechanism to remove
or unlearn MAC addresses for faster convergence on topology change.
It defines MAC List TLV which contains a list of MAC addresses to be
flushed in LDP Address Withdraw Message, and when a MAC List TLV
contains a large number of MAC addresses, it would be preferable to
send a LDP Address Withdraw Message with an empty MAC List.
As per the rules in [RFC4762], on receiving a MAC Address Withdrawal
Message with MAC List TLV, a PE removes the association between the
MAC address and the AC or PW over which this message is received.
For a MAC Address Withdraw message with empty MAC list, a PE removes
all MAC addresses except the MAC addresses learned over the newly
activated PW. The PE further transmits a MAC Address Withdrawal
message to each remote PE in the VPLS network. The problem is that
it will flush MAC addresses which are not affected due to topology
change, thus leading to unnecessary flooding and relearning.
Draft [I-D.ietf-l2vpn-vpls-ldp-mac-opt] defines an extension to the
MAC Address Withdrawal procedure with empty MAC List ([RFC4762]). It
is accomplished by sending an LDP Address Withdraw Message with the
empty MAC addresses and PE-ID TLV. When a PE device receives a MAC
Address Withdrawal message with a PE-ID TLV, it SHOULD flush all the
MAC addresses learned from the PW, which terminates in the remote VSI
identified by the PE-ID element. Comparing with [RFC4762], this
mechanism narrows the scope of MAC address flush to PE-ID elements.
But if this mechanism is used in VPLS model 3 ([RFC4664]) supporting
qualified learning ([RFC4762]), it also flushes MAC addresses
belonging to MAC address space which are not affected due to topology
change.
This draft describes the problem and a solution to optimize the MAC
flush procedure in [RFC4762] and [I-D.ietf-l2vpn-vpls-ldp-mac-opt],
and enable it to flush only the MAC addresses belonging to the MAC
address space affected by topology change.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119.
2.1. Terminology
AC: Attachment Circuit
CE: Customer Edge device
LDP: Label Distribution Protocol
PE: Provider Edge
PW: Pseudowire
MTU-s: Multi-Tenant Unit switch
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3. Problem Description
VLAN1
VLAN2 VLAN2
CE-2 CE-3
/ /
PE-1 / PE-3 /
+--------+/ +--------+/
| | | |
| -- | PW2 | -- |
VLAN1 | / \ |------------------| / \ |
CE-1 /------| \ s/ | | \S / |
\ primary spoke PW | -- | /------| -- |
\ / +--------+ / +--------+
\ (MTU-s)/ | \ PW3 / PW6|
+--------+/ | \ / |
| | | \ / |
| -- | PW1 | \ / |
| / \ | | H-VPLS Full Mesh Core|
| \S / | | / \ |
| -- | | / \ |
+--------+\ | PW4/ \ |
backup spoke PW | / \ |
\ +--------+ \--------+--------+
\ | | | |
\------| -- | PW5 | -- |
| / \ |------------------| / \ |
| \s / | | \S / |
| -- | | -- |
/+--------+ +--------+
/ PE-2 PE-4
/
CE-4
VLAN1
VLAN2
Figure 1: Dual homed MTU-s in two tier hierarchy H-VPLS
Figure 1 is an example for the dual-homing access topology in VPLS
model 3 supporting qualified learning.
There are four VLANs in Figure 1, and each customer VLAN has its own
broadcast domain and MAC address space. CE-1 and CE-3 belong to
VLAN1, CE-2 and CE-4 belong to VLAN2.
CE-1, CE-2, CE-3 and CE-4 connect with MTU-S, PE-1, PE-4 and PE-2
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respectively. 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.
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 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 belonging to VLAN1 and learned from the PW
that terminates at PE-1 MUST be removed. Once the backup PW has been
made active, MTU-s may send a MAC flush message to PE-2.
As per the rules defined in [RFC4762], PE-2 flushes all of the MAC
addresses learned in the VPLS from the PWs terminating at PE-1, PE-3
and PE-4. PE-2 further relays MAC flush messages to PE-1, PE-3 and
PE-4. Same processing rule applies at all those PE.
As per the rules defined in [I-D.ietf-l2vpn-vpls-ldp-mac-opt], PE-2
flushes all of the MAC addresses learned in the VPLS from the PWs
terminating at PE-1. In fact, PE2 need not flush the MAC addresses
belonging to VLAN2 and learned over PW1.There are multi-Mac addresses
spaces in a single VPLS, and the affected Mac addresses spaces is
only VLAN1. PE-2 only need flush and relearn MAC addresses belong to
VLAN1 and learned over PW1.
With the number of PE 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.
4. Optimized MAC Flush Mechanism
4.1. MAC Address Space TLV
This draft proposes a MAC Address Space TLV, it is carried in the LDP
Address Withdraw Message. The MAC Address Space TLV carries a MAC
address Space which are affected due to topology change. When a PE
receives a LDP Address Withdraw message with MAC Address Space TLV,
then the PE only flushes the suspect MAC addresses belonging to the
MAC Address Space elements.
The new MAC Address Space TLV format is as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| MAC Address Space TLV(TBD)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC address space |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MAC Address Space TLV format
U bit: Unknown bit. This bit MUST be set to 1. If the MAC address
Space format is not understood, then it MUST be ignored.
F bit: Forward bit. This bit MUST be set to 0. Since the LDP
mechanism used here is targeted, the TLV MUST NOT be forwarded.
Type: Type field. This identifies the TLV type as MAC Address Space
TLV.
Length: Length field. This field specifies the total length in
octets of value in MAC Address Space TLV.
MAC Address Space: This identifies the MAC addresses Space which are
affected due to topology change.
The MAC address space TLV should immediately be after the MAC address
list TLV. It is used to indicate MAC address space that these MAC
address list belongs to.
4.2. MAC Address Space TLV Processing Rules
If a PE receives a MAC Address Withdraw with MAC Address Space TLV
and empty MAC list, it SHOULD remove all the MAC addresses belonging
to the MAC Address Spaces in a VPLS instance, except the MAC
addresses learned over the PW associated with this signaling session
over which the message was received.
If a PE receives a MAC Address Withdraw with MAC Address Space TLV
and MAC list TLV, it SHOULD remove the MAC address belonging to the
MAC Address Space in a VPLS instance.
If a PE receives a MAC Address Withdraw with MAC Address Space TLV
and PE-ID TLV, from the specified MAC Address Space which is
identified by MAC Address Space TLV, it SHOULD remove all the MAC
addresses learned from the PW, which terminates at the PE identified
by the PE-ID.
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If a PE that doesn't support MAC Address Space TLV, receives a MAC
flush message with this option, it MUST ignore the option and follow
the processing rules as per [RFC4762] and
[I-D.ietf-l2vpn-vpls-ldp-mac-opt].
4.3. Optimized MAC Flush Procedures
This section explains the optimized MAC flush procedure in the
scenario shown in Figure 1.
When the backup PW is activated by MTU-s, it may send MAC Address
Withdraw message to PE-2 with the optional PE-ID TLV and MAC Address
Space TLV. Upon receipt of the MAC Address Withdraw message, PE-2
identifies the VPLS instance that requires MAC Address Withdraw 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. From the MAC Address
Space TLV, PE-2 identifies MAC addresses Space which are affected due
to topology change. PE-2 removes all MAC addresses belong to VLAN1
and learned over PW1.
PE-2 relays MAC Address Withdraw messages with the received MAC
Address Space TLV and PE-ID to all its peer PE devices. When the
message is received at PE-3/PE-4, MAC addresses belonging to VLAN1
and learned over the PW that terminates at PE1 MUST be removed.
5. IANA Considerations
The type field in the MAC List TLV is defined as 0x406 and is subject
to IANA approval
6. Security Considerations
Security considerations discussed in [RFC4762] and [I-D.ietf-l2vpn-
vpls-ldp-mac-opt] apply to this document.
7. Normative references
[I-D.ietf-l2vpn-vpls-ldp-mac-opt]
Dutta, P., Balus, F., Calvignac, G., and O. Stokes, "LDP
Extensions for Optimized MAC Address Withdrawal in
H-VPLS", draft-ietf-l2vpn-vpls-ldp-mac-opt-03 (work in
progress), October 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[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.
[RFC4664] Andersson, L. and E. Rosen, "Framework for Layer 2 Virtual
Private Networks (L2VPNs)", RFC 4664, September 2006.
[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.
Authors' Addresses
Ran Chen
ZTE Corporation
4F,RD Building 2,Zijinghua Road
Yuhuatai District,Nanjing 210012
P.R.China
Phone: +86 025 52878135
Email: chen.ran@zte.com.cn
Yubao Wang
ZTE Corporation
4F,RD Building 2,Zijinghua Road
Yuhuatai District,Nanjing 210012
P.R.China
Phone: +86 025 52872130
Email: wang.yubao2@zte.com.cn
Liang Guo
China Telecom
26/F,109 Zhongshan Ave
Tianhe District,Guangzhou 510630
P.R.China
Phone: +86 020 38639595
Email: guoliang@gsta.com
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