Internet DRAFT - draft-ietf-l2vpn-etree-frwk
draft-ietf-l2vpn-etree-frwk
L2VPN WG Raymond Key (editor)
Internet Draft Lucy Yong, Huawei (editor)
Intended status: Informational Simon Delord
Expires: February 2015 Telstra
Frederic Jounay, Orange CH
Lizhong Jin
August 25, 2014
A Framework for Ethernet Tree (E-Tree) Service over a Multiprotocol
Label Switching (MPLS) Network
draft-ietf-l2vpn-etree-frwk-10.txt
Abstract
This document describes an Ethernet-Tree (E-Tree) solution framework
for supporting the Metro Ethernet Forum (MEF) E-Tree service over a
Multiprotocol Label Switching (MPLS) network. The objective is to
provide a simple and effective approach to emulate E-Tree services
in addition to Ethernet LAN (E-LAN) services on an existing MPLS
network.
Status of this Memo
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Table of Contents
1. Introduction...................................................3
1.1. Terminology...............................................3
2. Overview.......................................................4
2.1. Ethernet Bridge Network...................................4
2.2. MEF Multipoint Ethernet Services: E-LAN and E-Tree........4
2.3. IETF L2VPN................................................5
2.3.1. Virtual Private LAN Service (VPLS)...................5
2.3.2. Ethernet VPN (EVPN)..................................5
2.3.3. Virtual Private Multicast Service (VPMS).............6
3. E-Tree Architecture Reference Model............................6
4. E-Tree Use Cases...............................................8
5. L2VPN Gaps for Emulating MEF E-Tree Service....................9
5.1. No Differentiation on AC Role.............................9
5.2. No AC Role Indication or Advertisement....................9
5.3. Other Issues..............................................9
6. Security Considerations.......................................10
7. IANA Considerations...........................................10
8. References....................................................11
8.1. Normative References.....................................11
8.2. Informative References...................................11
9. Contributing Authors..........................................12
10. Acknowledgments..............................................12
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1. Introduction
This document describes an Ethernet-Tree (E-Tree) solution framework
for supporting the Metro Ethernet Forum (MEF) E-Tree service over a
Multiprotocol Label Switching (MPLS) network. The objective is to
provide a simple and effective approach to emulate E-Tree services in
addition to Ethernet LAN (E-LAN) services on an existing MPLS
network.
This document extends the existing IETF specified Layer 2 Virtual
Private Network (L2VPN) framework [RFC4664] to provide the emulation
of E-Tree services over an MPLS network. It specifies the E-Tree
architecture reference model and describes the corresponding
functional components. It also points out the gaps and required
extension areas in existing L2VPN solutions such as Virtual Private
LAN Service (VPLS)[RFC4761][RFC4762] and Ethernet Virtual Private
Network (EVPN)[EVPN] for supporting E-Tree services.
1.1. Terminology
This document adopts all the terminologies defined in RFC4664
[RFC4664], RFC4761 [RFC4761], and RFC4762 [RFC4762]. It also uses the
following terminologies:
Leaf Attachment Circuit (AC): An AC with Leaf role. An ingress
Ethernet frame at a Leaf AC (Ethernet frame arriving over an AC at
the provider edge (PE) of an MPLS network) can only be delivered to
one or more Root ACs in an E-Tree service instance. An ingress
Ethernet frame at a Leaf AC must not be delivered to any Leaf ACs in
the E-Tree service instance.
Root AC: An AC with Root role. An ingress Ethernet frame at a Root AC
can be delivered to one or more of the other ACs in the associated E-
Tree service instance.
E-Tree: An Ethernet VPN service in which each AC is assigned the role
of a Root or Leaf. The forwarding rules in E-Tree are: Root AC can
communicate with other Root ACs and Leaf ACs; Leaf ACs can only
communicate with Root ACs.
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2. Overview
2.1. Ethernet Bridge Network
In this document, Ethernet bridge network refers to the Ethernet
bridge/switch network defined in IEEE802.1Q [IEEE802.1Q]. In a bridge
network, a data frame is an Ethernet frame; data forwarding is based
on destination MAC address; MAC reachability is learned in the data
plane based on the source MAC address and the port (or tagged port)
on which the frame arrives; and the MAC aging mechanism is used to
remove inactive MAC addresses from the MAC forwarding table on an
Ethernet switch.
Data frames arriving at a switch may be destined to known unicast MAC
destinations, unknown, multicast, or broadcast MAC destinations.
Unknown, multicast, and broadcast frames are forwarded in a similar
way, i.e. to every port except the ingress port on which the frame
arrives. Multicast forwarding can be further constrained when using
multicast control protocol snooping or multicast MAC registration
protocols. [IEEE802.1Q]
An Ethernet host receiving an Ethernet frame checks the destination
address in the frame to decide whether it is the intended
destination.
2.2. MEF Multipoint Ethernet Services: E-LAN and E-Tree
MEF6.1 [MEF6.1] defines two multipoint Ethernet Service types:
o E-LAN (Ethernet LAN), a multipoint-to-multipoint service
o E-Tree (Ethernet Tree), a rooted-multipoint service
MEF defines User-Network Interface (UNI) in a multipoint service as
the Ethernet interface between a Customer Equipment (CE) and a
Provider Edge (PE), i.e. the PE can send and receive Ethernet frames
to/from the CE. MEF also defines UNI roles in a multipoint service.
One role is Root and another is Leaf.
Note that MEF UNI in a service is equivalent to the Attachment
Circuit (AC) defined in L2VPN [RFC4664]. The Root AC and Leaf AC
defined in this document are the same as of the root UNI and leaf UNI
defined in MEF10.3 [MEF10.3]. The Root AC and Leaf AC terms are used
in the following MEF service description.
For an E-LAN service, all ACs have the Root role, which means that
any AC can communicate with other ACs in the service. The E-LAN
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service defined by MEF may be implemented by IETF L2VPN solutions
such as VPLS and EVPN [EVPN].
An E-Tree service has one or more Root ACs and at least two Leaf ACs.
An E-Tree service supports the communication among the roots and
between a root and a leaf but prohibits the communication among the
leaves. Existing IETF L2VPN solutions can't support the E-Tree
service. This document specifies the E-Tree architecture reference
model that supports the E-Tree service defined by MEF [MEF6.1].
Section 4 will discuss different E-Tree use cases.
2.3. IETF L2VPN
2.3.1. Virtual Private LAN Service (VPLS)
VPLS [RFC4761] [RFC4762] is an L2VPN solution that provides
multipoint-to-multipoint Ethernet connectivity across IP/MPLS
networks. VPLS emulates traditional Ethernet Virtual LAN Services
(VLAN) in MPLS networks, and may support MEF E-LAN services.
A data frame in VPLS is an Ethernet frame. Data forwarding in a VPLS
instance is based on the destination MAC address and the VLAN on
which the frame arrives. MAC reachability learning is performed in
the data plane based on the source address and the AC or Pseudowire
(PW) on which the frame arrives. MAC aging is also the mechanism used
to remove inactive MAC addresses from a VPLS switching instance (VSI)
on a Provider Edge (PE). VPLS supports forwarding for known unicast,
unknown unicast, broadcast, and multicast Ethernet frames.
Many service providers have deployed VPLS in their networks to
provide L2VPN services to customers.
2.3.2. Ethernet VPN (EVPN)
Ethernet VPN [EVPN] is an enhanced L2VPN solution that emulates an
Ethernet LAN or virtual LAN(s) across MPLS networks.
EVPN supports active-active multi-homing of CEs and uses
Multiprotocol Border Gateway Protocol (MP-BGP) control plane to
advertise MAC address reachability from an ingress PE to egress PEs.
Thus, a PE learns MAC addresses reachable over local ACs in the data
plane and other MAC addresses reachable across the MPLS network over
remote ACs via the EVPN MP-BGP control plane. As a result, EVPN aims
to support large-scale L2VPN with better resiliency compared to VPLS.
EVPN is relatively new technique and is still under development in
IETF L2VPN WG.
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2.3.3. Virtual Private Multicast Service (VPMS)
VPMS [VPMS] is an L2VPN solution that provides point-to-multipoint
connectivity across MPLS networks and supports various attachment
circuit (AC) types, including Frame Relay, ATM, Ethernet, PPP, etc.
In the case of Ethernet ACs, VPMS provides single coverage of
receiver membership, i.e. there is no differentiation among multicast
groups in one VPN. Destination address in the Ethernet frame is not
used in data forwarding.
VPMS supports unidirectional point-to-multipoint transport from a
sender to multiple receivers and may support reverse transport in a
point-to-point manner.
3. E-Tree Architecture Reference Model
Figure 1 illustrates E-Tree architecture reference model. Three
provider edges (PEs), PE1, PE2, and PE3 are shown in the Figure. Each
PE has a Virtual Service Instance (VSI) associated with an E-Tree
service instance. A CE attaches to the VSI on a PE via an AC. Each AC
must be configured with a root or leaf role. In Figure 1, AC1 AC2,
AC5, AC6, AC9, AC10 are Root ACs; AC3, AC4, AC7, AC8, AC11, AC12 are
Leaf ACs. This implies that a PE (local or remote) processes the
Ethernet frames from CE01, CE02, etc as if they are originated from a
Root AC; and processes the Ethernet frames from CE03, CE04, etc as if
they are originated from a Leaf AC.
Under this architecture model, the forwarding rules among the ACs,
regardless whether sending AC and receiving AC are on the same PE or
on different PEs, are described as follow:
o An egress frame (frame to be transmitted over an AC) at an AC with
Root role must be the result of an ingress frame at an AC (frame
received at an AC) that has Root or Leaf role attached to the same
E-tree service instance.
o An egress frame at the AC with Leaf role must be the result of an
ingress frame at an AC that has Root role attached to the same E-
tree service instance.
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<------------E-Tree----------->
PE1+---------+ +---------+PE2
+----+ | +---+ | | +---+ | +----+
|CE01+----AC1----+--+ | | | | +--+----AC5----+CE05|
+----+ (Root AC) | | V | | | | V | | (Root AC) +----+
+----+ | | | | | | | | +----+
|CE02+----AC2----+--+ | | | | +--+----AC6----+CE06|
+----+ (Root AC) | | S +--+---------+--+ S | | (Root AC) +----+
+----+ | | | | | | | | +----+
|CE03+----AC3----+--+ | | | | +--+----AC7----+CE07|
+----+ (Leaf AC) | | I | | | | I | | (Leaf AC) +----+
+----+ | | | | | | | | +----+
|CE04+----AC4----+--+ | | | | +--+----AC8----+CE08|
+----+ (Leaf AC) | +-+-+ | | +-+-+ | (Leaf AC) +----+
+----+----+ +----+----+
| MPLS Core |
| +----+----+
| | +-+-+ | +----+
| | | +--+----AC9----+CE09|
| | | V | | (Root AC) +----+
| | | | | +----+
| | | +--+----AC10---+CE10|
+--------------+--+ S | | (Root AC) +----+
| | | | +----+
| | +--+----AC11---+CE11|
| | I | | (Leaf AC) +----+
| | | | +----+
| | +--+----AC12---+CE12|
| +---+ | (Leaf AC) +----+
PE3 +---------+
<-------------E-Tree---------->
Figure 1 E-Tree Architecture Reference Model
These rules apply to all frame types, i.e. Known Unicast, Unknown,
Broadcast, and Multicast. For Known Unicast frames, forwarding in a
VSI context is based on the destination MAC address.
A VSI on a PE corresponds to an E-Tree service instance and maintains
a MAC forwarding table which is isolated from other VSI tables on the
PE. It also keeps the track of local AC roles. The VSI receives a
frame from an AC or across the MPLS core; and forwards the frame to
another AC over which the destination is reachable according to the
VSI forwarding table and forwarding rules described above. When the
target AC is on a remote PE, the VSI forwards the frame to the remote
PE over the MPLS core. Forwarding over the MPLS core will be
dependent on the E-tree solution. For instance, a solution may adopt
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PWs to mesh VSIs as in VPLS, and forward frames over VSIs subject to
the E-tree forwarding rules. Alternatively, a solution may adopt the
EVPN forwarding paradigm constrained by the E-tree forwarding rules.
Thus, solutions that satisfy the E-tree requirements could be
extensions to VPLS and EVPN.
In most use cases, an E-Tree service has only a few Root ACs (root CE
sites) but many Leaf ACs (leaf CE sites). Furthermore, a PE may have
only Root ACs or only Leaf ACs. Figure 1 provides a general E-Tree
architecture model.
4. E-Tree Use Cases
Table 1 below presents some major use cases for E-Tree.
+---------------------------+--------------+------------+
| Use Case | Root AC | Leaf AC |
+---+---------------------------+--------------+------------+
| 1 | Hub & Spoke VPN | Hub Site | Spoke Site |
+---+---------------------------+--------------+------------+
| 2 | Wholesale Access | Customer's | Customer's |
| | | Interconnect | Subscriber |
+---+---------------------------+--------------+------------+
| 3 | Mobile Backhaul | RAN NC | RAN BS |
+---+---------------------------+--------------+------------+
| 4 | IEEE 1588 PTPv2 [1588] | PTP Server | PTP Client |
| | Clock Synchronization | | |
+---+---------------------------+--------------+------------+
| 5 | Internet Access | BNG Router | Subscriber |
| | Reference: [TR-101] | | |
+---+---------------------------+--------------+------------+
| 6 | Broadcast Video | Video Source | Subscriber |
| | (unidirectional only) | | |
+---+---------------------------+--------------+------------+
| 7 | Broadcast/Multicast Video | Video Source | Subscriber |
| | plus Control Channel | | |
+---+---------------------------+--------------+------------+
| 8 | Device Management | Management | Managed |
| | | System | Device |
+---+---------------------------+--------------+------------+
Where:
RAN: Radio Access Network NC: Network Controller
BS: Base Station PTP: Precision Time Protocol
BNG: Broadband Network Gateway
Table 1 E-Tree Use Cases
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Common to all use cases, direct Layer2 Leaf-to-Leaf communication is
required to be prohibited. For Mobile backhaul, this may not be valid
for LTE X2 interfaces; LTE X2 interface [LTE] between two evolved
node B (eNB) enables the communication in between. E-Tree service is
appropriate for such use cases.
Also common to the use cases mentioned above, there may be single or
multiple Root ACs in one E-Tree service. The need of multiple Root-
ACs may be driven by redundancy requirement or multiple serving
sites. Whether a particular E-Tree service needs to support single or
multiple Root ACs depends on an application.
5. L2VPN Gaps for Emulating MEF E-Tree Service
E-Tree Service defines special forwarding rules that prohibit
forwarding Ethernet frames among leaves. This poses some challenges
to IETF L2VPN solutions such as VPLS and EVPN in emulating E-Tree
service over an MPLS network. There are two major issues described in
the following sections.
5.1. No Differentiation on AC Role
IP/MPLS L2VPN architecture has no distinct role on Attachment Circuit
(AC) and supports any-to-any connectivity among all ACs. It does not
have any mechanism to support forwarding constraint based on an AC
role. However, E-Tree service defines two AC roles, Root and Leaf,
and defines the forwarding rules based on the frame originating and
receiving AC roles.
5.2. No AC Role Indication or Advertisement
In an L2VPN, when a PE, say PE2, receives a frame from another PE,
say PE1, over the MPLS core, PE2 does not know if the frame from PE1
is originated from a root AC or leaf AC. This causes the forwarding
issue on PE2 because the E-Tree forwarding rules require that the
forwarder must know the role of the frame origin, i.e. from root AC
or leaf AC. This is specifically important, when PE2 has both root AC
and leaf AC attached to the VSI. E-Tree forwarding rules apply to all
types of frames (known unicast destination, unknown unicast
destination, multicast and broadcast).
5.3. Other Issues
Some desirable requirements for IETF E-Tree are specific to an
IP/MPLS L2VPN implementation such as Leaf-only PE. Leaf-only PE is
the PE that only has Leaf AC(s) in an E-Tree service instance, thus
other PEs on the same E-Tree service instance do not necessarily
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forward the frames originated from a Leaf AC to the Leaf-only PE,
which may save some network resources. It is also desirable for E-
Tree solution to work with existing PEs that support single-role AC
and the role is equivalent to the root in an E-Tree Service. These
requirements are described in the E-Tree requirement document.
[RFC7152]
6. Security Considerations
An E-tree service may be deployed for security reasons to prohibit
communication among sites (leaves). An E-tree solution must enforce
E-Tree forwarding constraints. The solution must also guarantee that
Ethernet frames do not leak outside of the E-tree service instance to
which they belong.
An E-Tree service prohibits communication among leaf sites but does
not have knowledge of higher layer security constraint. Therefore, in
general, higher layer applications can not rely on E-Tree to provide
the security protection unless all security constraints are fully
implemented by E-Tree service.
Enhancing L2VPN for E-Tree service inherits the same security issues
described in L2VPN framework [RFC4664]. These relate to both control
plane and data plane security issues that may arise in the following
areas:
o issues fully contained in the provider network
o issues fully contained in the customer network
o issues in the customer-provider interface network
The framework has substantial discussions on the security issues and
potential solutions to address them. An E-Tree solution must consider
these issues and address them properly. VPLS [RFC4761] [RFC4762]
and/or EVPN [EVPN] will likely be candidate solutions for E-Tree
Service over MPLS network. The security capabilities built in these
solutions will be naturally adopted in supporting E-Tree. For the
detail, see the security consideration section in [RFC4761],
[RFC4762], and [EVPN].
7. IANA Considerations
The document requires no IANA action.
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8. References
8.1. Normative References
[MEF6.1] MEF, "Metro Ethernet Forum, Ethernet Services Definitions -
Phase 2", MEF6.1, April 2008
[MEF10.3] MEF, "Ethernet Service Attributes Phase 3", MEF10.3,
October 2013
[RFC4664] Andersson, L., et al, "Framework for Layer 2 Virtual
Private Network (L2VPNs)", RFC4664, Sept. 2006
[RFC4761] Kompella & Rekhter, "Virtual Private LAN Service (VPLS)
Using BGP for Auto-Discovery and Signaling", RFC4761,
January 2007
[RFC4762] Lasserre & Kompella, "Virtual Private LAN Service (VPLS)
Using Label Distribution Protocol (LDP) Signaling",
RFC4762, January 2007
[RFC7152] Key, et al., "Requirements for Metro Ethernet Forum (MEF)
Ethernet-Tree (E-Tree) Support in L2VPN", RFC7152, April
2011997.
8.2. Informative References
[IEEE802.1Q] IEEE802.1, "Media Access Control (MAC) Bridges and
Virtual Bridged Local Area", IEEE802.1Q, 2011
[1588] IEEE 1588, "Precision Time Protocol", IEEE 1588, 2013
[LTE] 3GPP TS, "Evolved Universal Terrestrial Radio Access (E-
UTRA) and Evolved Universal Terrestrial Radio Access
Network (E-UTRAN)", V11.2.0, June, 2012
[TR-101] Broadband Forum, "Migration to Ethernet-Based Broadband
Aggregation Issue 2", July 2011
[VPMS] Kamite, et al., "Framework and Requirements for Virtual
Private Multicast Service (VPMS)", draft-ietf-l2vpn-vpms-
frmwk-requirements-05, work in progress
[EVPN] Sajassi, et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
l2vpn-evpn-07, work in progress
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9. Contributing Authors
The following people contribute the document as co-authors.
Yuji Kamite
NTT Communications Corporation
Granpark Tower
3-4-1 Shibaura, Minato-ku
Tokyo 108-8118, Japan
Email: y.kamite@ntt.com
Wim Henderickx
Alcatel-Lucent
Copernicuslaan 50
2018 Antwerp, Belgium
Email: wim.henderickx@alcatel-lucent.com
10. Acknowledgments
Authors like to thank Nabil Bitar for this detail review and
suggestions.
Authors' Addresses
Raymond Key (editor)
Email: raymond.key@ieee.org
Lucy Yong (editor)
Huawei USA
Email: lucy.yong@huawei.com
Simon Delord
Telstra
Email: simon.delord@gmail.com
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Frederic Jounay
Orange CH
4 rue caudray 1020 Renens
Switzerland
Email: frederic.jounay@orange.ch
Lizhong Jin
Email: lizho.jin@gmail.com
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