E-TREE Support in E-VPN
draft-sajassi-l2vpn-evpn-etree-00
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| Document | Type |
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|---|---|---|---|
| Authors | Ali Sajassi , Samer Salam | ||
| Last updated | 2012-07-02 | ||
| Replaced by | draft-sajassi-bess-evpn-etree | ||
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draft-sajassi-l2vpn-evpn-etree-00
L2VPN Workgroup Ali Sajassi
INTERNET-DRAFT Samer Salam
Intended Status: Standards Track Cisco
Expires: December 29, 2012 June 29, 2012
E-TREE Support in E-VPN
draft-sajassi-l2vpn-evpn-etree-00
Abstract
The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
Ethernet service known as Ethernet Tree (E-Tree). [ETREE-FRAMEWORK]
proposes a solution framework for supporting this service in MPLS
networks. This document discusses how those functional requirements
can be easily met with E-VPN.
Status of this Memo
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Copyright and License 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
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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
carefully, as they describe your rights and restrictions with respect
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2 E-Tree Scenarios and E-VPN Support . . . . . . . . . . . . . . 3
2.1 Scenario 1: Leaf OR Root site(s) per PE . . . . . . . . . . 3
2.2 Scenario 2: Leaf AND Root site(s) per PE . . . . . . . . . . 5
2.3 Scenario 3: Leaf AND Root site(s) per Ethernet Segment . . . 6
3 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . . . . 7
3.2 E-Tree without MAC Learning . . . . . . . . . . . . . . . . 8
4 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 8
5 Security Considerations . . . . . . . . . . . . . . . . . . . . 8
6 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
7 References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1 Normative References . . . . . . . . . . . . . . . . . . . 8
7.2 Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1 Introduction
The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
Ethernet service known as Ethernet Tree (E-Tree). In an E-Tree
service, endpoints are labeled as either Root or Leaf sites. Root
sites can communicate with all other sites. Leaf sites can
communicate with Root sites but not with other Leaf sites.
[ETREE-FRAMEWORK] proposes the solution framework for supporting E-
Tree service in MPLS networks. The document identifies the functional
components of the overall solution to emulate E-Tree services in
addition to Ethernet LAN (E-LAN) services on an existing MPLS
network.
[EVPN] is a solution for multipoint L2VPN services, with advanced
multi-homing capabilities, using BGP for distributing customer/client
MAC address reach-ability information over the MPLS/IP network.
This document discusses how the functional requirements for E-Tree
service can be easily met with E-VPN.
1.1 Terminology
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 [RFC2119].
2 E-Tree Scenarios and E-VPN Support
In this section, we will categorize support for E-Tree into three
different scenarios, depending on the nature of the site association
(Root/Leaf) per PE or per Ethernet Segment:
- Leaf OR Root site(s) per PE
- Leaf AND Root site(s) per PE
- Leaf AND Root site(s) per Ethernet Segment
For each scenario, we will describe the E-VPN mechanism for
supporting the E-Tree service.
2.1 Scenario 1: Leaf OR Root site(s) per PE
In this scenario, a PE may have Root sites OR Leaf sites for a given
VPN instance, but not both concurrently. The PE may have both Root
and Leaf sites albeit for different VPNs. Every Ethernet Segment
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connected to the PE is uniquely identified as either a Root or a Leaf
site.
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+-----ES1----+--+ | | | MPLS | | | +--+----ES2-----+CE2|
+---+ (Root) | | E | | | /IP | | | E | | (Leaf) +---+
| | V | | | | | | V | |
| | I | | | | | | I | | +---+
| | | | | | | | +--+----ES3-----+CE3|
| +---+ | +------+ | +---+ | (Leaf) +---+
+---------+ +---------+
Figure 1: Scenario 1
One approach for addressing this scenario involves associating two
BGP Route-Targets (RTs) with every E-VPN Instance (EVI): one RT is
associated with the Root sites and the other is associated with the
Leaf sites. On a per EVI basis, every PE exports the single RT
associated with its type of site(s). Furthermore, a PE with Root
site(s) imports both Root and Leaf RTs, whereas a PE with Leaf
site(s) only imports the Root RT. This approach suffers from two
shortcomings:
- Additional configuration overhead, as it requires the network
operator to configure two RTs per EVI.
- Introduces a scalability limitation where only 32K E-Tree EVIs can
be supported (due to 2 bytes RT value, and the fact that two RTs are
required per EVI).
To alleviate both of these issues, we propose a new BGP Extended
Community attribute encoded as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Sub-Type | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where,
Type = To be assigned by IANA
Sub-Type = 1 byte, value TBA1 denotes Root, value TBA2 denotes Leaf
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Value = 6 bytes uniquely identifying an EVI.
This extended community is a new transitive extended community, and
will be referred to as the EVI-Import Extended Community. This
extended community is used in lieu of the RT on the following E-VPN
routes:
- MAC Advertisement Routes
- Ethernet A-D Routes
- Inclusive Multicast Routes
On a per EVI basis, every PE exports routes with the single EVI-
Import extended community associated with its type of site(s).
Furthermore, a PE with Root site(s) imports routes with both Root and
Leaf EVI-Import extended community. Whereas, a PE with Leaf site(s)
only imports the Root EVI-Import extended community.
2.2 Scenario 2: Leaf AND Root site(s) per PE
In this scenario, a PE may have a set of one or more Root sites AND a
set of one or more Leaf sites for a given VPN instance. Every
Ethernet Segment connected to the PE is uniquely identified as either
a Root or a Leaf site.
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+-----ES1----+--+ | | | | | | +--+----ES2-----+CE2|
+---+ (Leaf) | | E | | | MPLS | | | E | | (Leaf) +---+
| | V | | | /IP | | | V | |
| | I | | | | | | I | | +---+
| | | | | | | | +--+----ES3-----+CE3|
| +---+ | +------+ | +---+ | (Root) +---+
+---------+ +---------+
Figure 2: Scenario 2
This scenario requires that the MPLS-encapsulated frames be tagged
with an indication of whether they originated from a Root or a Leaf
Ethernet Segment, so that the proper connectivity constraints can be
enforced. This can be achieved in E-VPN through the use of the ESI
MPLS label, since this label identifies the Ethernet Segment of
origin of a given frame. For E-Tree service, the ESI MPLS label must
be used to encapsulate not only multi-destination frames (i.e.
broadcast, multicast & unknown unicast), but also known unicast
frames. The egress PE determines whether or not to forward a
particular frame to an Ethernet Segment depending on a combination of
the split-horizon rule defined in [EVPN] and on the E-Tree
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connectivity constraints:
- If the ESI Label indicates that the source Ethernet Segment is a
Root, then the frame can be forwarded on a segment granted that it
passes the split-horizon check.
- If the ESI Label indicates that the source Ethernet Segment is a
Leaf, then the frame can be forwarded only on a Root segment, granted
that it passes the split-horizon check.
When advertising the ESI MPLS label for a given Ethernet Segment, a
PE must indicate whether the corresponding ESI is a Root or a Leaf
site. This can be done by re-purposing one of the Reserved bits in
the Flags field of the ESI MPLS label Extended Community attribute
([EVPN] Section 8) to indicate Root/Leaf status.
2.3 Scenario 3: Leaf AND Root site(s) per Ethernet Segment
In this scenario, a PE may have a set of one or more Root sites AND a
set of one or more Leaf sites for a given VPN instance. An Ethernet
Segment connected to the PE may be identified as both a Root and a
Leaf site concurrently.
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+-----ES1----+--+ | | | | | | +--+----ES2-----+CE2|
+---+ (Leaf/Root)| | E | | | MPLS | | | E | | (Leaf/Root)+---+
| | V | | | /IP | | | V | |
| | I | | | | | | I | | +---+
| | | | | | | | +--+----ES3-----+CE3|
| +---+ | +------+ | +---+ | (Leaf) +---+
+---------+ +---------+
Figure 3: Scenario 3
This scenario can be addressed by extending the use of the ESI MPLS
label, as described in the previous section, so that for an Ethernet
Segment that has both Root and Leaf sites attached, two ESI MPLS
labels are allocated and advertised: one ESI MPLS label denotes Root
and the other denotes Leaf. The ingress PE imposes the right ESI MPLS
label depending on whether the Ethernet frame originated from the
Root or Leaf site on that Ethernet Segment. The mechanism by which
the PE identifies whether a given frame originated from a Root or
Leaf site on the segment is outside the scope of this document.
In addition to advertising two ESI MPLS labels per Ethernet Segment
(for segments that have both Root and Leaf attached), a PE advertises
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two special ESI MPLS labels: one for Root and another for Leaf. These
are used by remote PEs for traffic originating from single-homed
segments and for multi-homed segments that are not connected to the
advertising PE.
3 Operation
Per [ETREE-FRAMEWORK], a generic E-Tree service supports all of the
following traffic flows:
- Ethernet Unicast from Root to Leaf
- Ethernet Unicast from Leaf to Root
- Ethernet Unicast from Root to Root
- Ethernet Broadcast/Multicast from Root to Roots & Leafs
- Ethernet Broadcast/Multicast from Leaf to Roots
A particular E-Tree service may need to support all of the above
types of flows or only a select subset, depending on the target
application. In the case where unicast flows need not be supported,
the L2VPN PEs can avoid performing any MAC learning function.
In the subsections that follow, we will describe the operation of E-
VPN to support E-Tree service with and without MAC learning.
3.1 E-Tree with MAC Learning
The PEs implementing an E-Tree service must perform MAC learning when
unicast traffic flows must be supported from Root to Leaf or from
Leaf to Root sites. In this case, the PE with Root sites performs MAC
learning in the data-path over the Ethernet Segments, and advertises
reachability in E-VPN MAC Advertisement routes. These routes will be
imported by PEs that have Leaf sites as well as by PEs that have Root
sites, in a given EVI. Similarly, the PEs with Leaf sites perform MAC
learning in the data-path over their Ethernet Segments, and advertise
reachability in E-VPN MAC Advertisement routes which are imported
only by PEs with at least one Root site in the EVI. A PE with only
Leaf sites will not import these routes. PEs with Root and/or Leaf
sites may use the Ethernet A-D routes for aliasing (in the case of
multi-homed segments) and for mass MAC withdrawal.
To support multicast/broadcast from Root to Leaf sites, either a P2MP
tree rooted at the PE(s) with the Root site(s) or ingress replication
can be used. The multicast tunnels are set up through the exchange of
the E-VPN Inclusive Multicast route, as defined in [E-VPN].
To support multicast/broadcast from Leaf to Root sites, ingress
replication should be sufficient for most scenarios where there is a
single Root or few Roots. If the number of Roots is large, a P2MP
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tree rooted at the PEs with Leaf sites may be used.
3.2 E-Tree without MAC Learning
The PEs implementing an E-Tree service need not perform MAC learning
when the traffic flows between Root and Leaf sites are multicast or
broadcast. In this case, the PEs do not exchange E-VPN MAC
Advertisement routes. Instead, the Ethernet A-D routes are used to
exchange the E-VPN labels.
The fields of the Ethernet A-D route are populated per the procedures
defined in [E-VPN], and the route import rules are as described in
previous sections.
4 Acknowledgement
We would like to thank Sami Boutros for his comments.
5 Security Considerations
Same security considerations as [E-VPN].
6 IANA Considerations
Allocation of Extended Community Type and Sub-Type for E-VPN.
7 References
7.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[ETREE-FRAMEWORK] Key et al., "A Framework for E-Tree Service over
MPLS Network", draft-ietf-l2vpn-etree-frwk-00, work in
progress, January 2012.
7.2 Informative References
[EVPN] Aggarwal et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
l2vpn-evpn-00.txt, work in progress, February, 2012.
[ETREE-REQ] Key et al., "Requirements for MEF E-Tree Support in
VPLS", draft-ietf-l2vpn-etree-reqt-01.txt, work in progress, April,
2012.
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Authors' Addresses
Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134, US
Email: sajassi@cisco.com
Samer Salam
Cisco
595 Burrard Street, Suite 2123
Vancouver, BC V7X 1J1, Canada
Email: ssalam@cisco.com
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