One document matched: draft-jiang-l2vpn-vpls-ring-00.txt
Networking Working Group A. Jiang
Internet Draft X. Song
Intended status: Informational X. Qu
Expires: March, 2010 S. Wu
J. Luo
ZTE
October 16, 2009
VPLS Ring
draft-jiang-l2vpn-vpls-ring-00.txt
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Abstract
This document describes ring based VPLS architecture. This
architecture is an alternative to existing VPLS architecture. It can
simplify the full mesh connection overhead and provide a standard
based protection mechanism, especially when the underlying cable or
fiber infrastructure is ring based. It is also an optimal
architecture for customer multicast traffic compared with existing
VPLS.
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Table of Contents
1. Introduction.................................................2
2. Conventions used in this document............................3
3. Analysis of related documents................................3
4. Ethernet Ring Based VPLS.....................................3
4.1. Native Ethernet Ring....................................3
4.2. MPLS Services & Their Native Form.......................5
4.3. CE-PE Ring..............................................5
4.4. PE-PE Ring..............................................6
4.5. Inter-VPLS Ring.........................................6
4.6. Customer Multicast Traffic..............................7
5. Security Considerations......................................7
6. IANA Considerations..........................................7
7. Conclusions..................................................7
8. References...................................................7
8.1. Normative References....................................7
8.2. Informative References..................................8
9. Acknowledgments..............................................8
1. Introduction
VPLS is to use MPLS to deliver Ethernet service over WAN.
Currently, VPLS architecture is based on VPLS framework [RFC 4664].
And full mesh +split horizon is one of the most widely deployed modes.
In this mode, VSIs in the same service VPN connect with each other
via full mesh PWs, and use split horizon forwarding scheme. This
design is to prevent loop in the forwarding path.
Full mesh imposes heavy load on forwarding, control & management
plane, and not scalable. Hierarchical VPLS discussed in LDP VPLS [RFC
4762] (Hub-Spoke) and BGP VPLS [RFC 4761] (Route Reflector) are
proposed to fix the problem.
However, in certain scenario like ring network, it can be optimized.
Ring is a common network topology for many service provider's cable
or fiber infrastructure.
Mapping basic full mesh or hierarchical connections to ring is not
very elegant. It will also cause unnecessary customer multicast
traffic copies, which will be explained in following section.
There are some ring based Ethernet forwarding and protection designs
that we can use to construct a more elegant and simple VPLS solution.
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2. 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].
3. Analysis of related documents
There are several works on ring based VPLS.
1) VPLS protection switching with ring access [draft-song-l2vpn-vpls-
ring-access]
In this document, ring based technology is deployed in the access
part of VPLS, which includes CE and the connected PE. They can use
ring for multi-homing access and protection. It covers single, dual
and multiple CE multi-homing scenarios.
2) Pseudowire (PW) Redundancy Framework [draft-ietf-pwe3-redundancy]
In this document, PW redundancy is used to provide multi-homing
solution for VPLS. It has discussed the scenario of PW redundancy for
dual-homing between PEs in ring topology, and has a very brief
overview of the possible solutions.
3) BGP based VPLS Multi-homing [draft-kothari-henderickx-l2vpn-vpls-
multihoming]
This is to use BGP as provisioning mechanism for multi-homing VPLS.
4) There are also some ring solutions for MPLS-TP. But VPLS
forwarding is closely related to Ethernet, these 2 are inherently
different.
4. Ethernet Ring Based VPLS
4.1. Native Ethernet Ring
There are some documents on this topic.
In [ITU-T G.8032] Ethernet Ring Protection Switching, native Ethernet
ring protection protocol and switching mechanism is defined.
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In [RFC 3619] Ethernet Automatic Protection Switching, a similar
design is presented.
The main idea is to define a control node adjacent to a protection
link. As shown in figure below, Node 1 is the control node and the
link between 1 and 6 is the protection link.
2 ----- 1 o---- 6 2 ----- 1 ----- 6
| Ring | <----> | Ring |
3 ----- 4 ----- 5 3 ----- 4 o---- 5
Node 1 will block its port in the protection link to prevent loop.
When there is link or node failure, node adjacent to the failure will
detect the failure and inform the control node via protection control
protocol. Or control node itself can do the job via fault detection
protocol.
When control node is informed, it will unblock the previously blocked
port. When fault is cleared, control node will block the port again
to prevent loop.
In this example, when link between node 4 and 5 is broken, control
node 1 will detect the failure and will unblock port in the
protection link. When the failure is cleared, node 1 will block the
port in protection link again.
N ----- N o---- N
| Sub-ring |
N ----- N ----- 2 ----- 1 o---- 6 ----- N ----- N
o Sub-ring | Ring | Sub-ring o
N ----- N ----- 3 ----- 4 ----- 5 ----- N ----- N
| Sub-ring |
N o---- N ----- N
Interconnected rings are also supported, as shown above. This is a
hierarchical structure of a ring and several sub-rings. Ring is
viewed by sub-ring as a permanent link. Each sub-ring will run its
own ring control protocol for loop prevention and protection.
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4.2. MPLS Services & Their Native Form
MPLS provides a scalable encapsulation mechanism for multiple
services. MPLS has been adapted by wide range of services including
L3VPN, L2VPN (PW, VPLS), TE, FRR, multicast, QoS, BGP free core
network, transport (MPLS-TP), etc.
Some of these services are widely deployed and deemed a success, such
as L3VPN, L2VPN (PW, VPLS), TE and FRR. Some are still under
development, such as Transport and multicast. And some may have
difficulty to take off, such as BGP free core.
When we look at the winner, we can find that all successful MPLS
services are successful in their native form, and vice versa.
Native form of L3VPN is IP service, which is the foundation of
Internet and broadband network. Native form of PW is legacy WAN
services, which is dominant in traditional telecom world. Native form
of VPLS is Ethernet, which is dominant in enterprise world.
While multicast in its native form is not as widely deployed as
unicast due to its inherent complexity. So does multicast in MPLS
encapsulation.
If we apply the same rule to Ethernet ring, we expect its native form
to be deployed and accepted before its MPLS flavored version to be
success.
4.3. CE-PE Ring
(CE) ----- CE1 ------ PE1
o o |
(CE) ---- (CE2) ----- PE2
: : |
(CE)...... (CE)..... (PE)
Ring is formed among CE and PE. It can be 1 CE & 2 PE ring, 2 CE &
2PE ring, n CE & n PE ring. It can be single ring or interconnected
rings. PW between PE is treated by PE as virtual link. Ethernet ring
control protocol is running in CE and PE for loop prevention and
protection. We can use this mechanism to build scalable and flexible
VPLS access network. It is also the convenient way to build CE-PE
multi-homing.
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4.4. PE-PE Ring
PE ---- PE o --- PE
| Sub-ring |
PE----- PE-----PE ---- PE o --- PE----- PE -----PE ----- CE
O Sub-ring | Ring | Sub-ring o |
PE----- PE-----PE ---- PE ----- PE----- PE -----PE ----- CE
| Sub-ring |
PE o - PE ----- PE
Ring can be among PEs. It can be single ring or interconnected rings.
This design is simple & neat for service provider with ring
fiber/cable resources. PE ring can also interconnect with CE-PE ring.
Its forwarding process is different from that of VPLS. There is only
1 bi-directional PW between each pair of PEs serving as virtual link.
N PWs in this case compared with N*(N-1)/2 PWs in full mesh case for
N nodes is one of the benefits, other benefits include customer
multicast optimization, which will be explained in following section.
There is also certain cost. In ring, each PE will turn on MAC
learning. Ethernet packet will go through each PE in ring, and PE
will forward Ethernet packet based on MAC forwarding table.
The whole network is Ethernet ring using PW as virtual link between
nodes. MPLS protection mechanism is used to protect the PW locally.
Ethernet ring protection mechanism is used to protect the VPLS
service. It is also the convenient way to build PE redundancy.
4.5. Inter-VPLS Ring
(VPLS 1 Border PE) ----- (VPLS 2 Border PE) o --- (VPLS 2 Border PE)
| |
(VPLS 1 Border PE) ----- (VPLS 3 Border PE) ----- (VPLS 3 Border PE)
Ring can also be used to provide inter-VPLS connection. Each VPLS can
connect to other VPLS via border PE. inter-VPLS ring can also
interconnect with PE ring or CE-PE ring. Protection mechanism is
similar to PE ring. It also provides inter-VPLS PE redundancy.
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4.6. Customer Multicast Traffic
CE1 -----PE1 ==>== PE2 -->-- CE2
| |
V v
CE3 -----PE3 ---- PE4 -->-- CE4
In full mesh VPLS, there will be multiple copy of customer multicast
traffic in inter-PE PW and waste the bandwidth.
For example, multicast traffic from CE1 to CE2-4 will be sent in PW
from PE1 to PE2-4. There will be 2 copies of traffic in link between
PE1 and PE2. If the number of multicast receiving node is N, there
will be copies of traffic along the root to leaf path from around N/2
to 1.
In ring VPLS, there will be only 1 copy of customer multicast traffic
along the path from root to leaf. Its forwarding mechanism is similar
to Ethernet multicast forwarding mechanism.
5. Security Considerations
6. IANA Considerations
7. Conclusions
In this document, Ethernet ring based VPLS is presented. This
architecture is most suitable to be deployed on infrastructure with
fiber/cable ring. It can greatly reduce the number of inter-PE PWs in
full mesh design. It can also eliminate the unnecessary copies of
customer multicast traffic due to full mesh design. Ring can also
provide a convenient way for node and link protection.
8. References
8.1. Normative References
[RFC 2119] Bradner, S., Editor, "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC2119, March
1997.
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[RFC 4664] Andersson, L., Rosen, E., "Framework for Layer 2
Virtual Private Networks (L2VPNs)", RFC 4664,
September 2006.
8.2. Informative References
[VPLS RING ACCESS] Song, X., Wu, S., Shao, H., "VPLS protection
switching with ring access", ID draft-song-l2vpn-vpls-
ring-access-00, October 2008.
9. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
Albert Jiang
ZTE
Email: albert.john@zte.com.cn
Xiaojuan Song
ZTE
Email: song.xiaojuan@zte.com.cn
Yanfeng Qu
ZTE
Email: qu.yanfeng@zte.com.cn
Shaoyong Wu
ZTE
Email: wu.shaoyong@zte.com.cn
Jiang Luo
ZTE
Email: lu.jian@zte.com.cn
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