L2VPN Workgroup Ali Sajassi
INTERNET-DRAFT Samer Salam
Intended Status: Standards Track Cisco
Wim Henderickx
Alcatel-Lucent
Jim Uttaro
AT&T
Expires: April 22, 2012 October 22, 2012
E-TREE Support in E-VPN
draft-sajassi-l2vpn-evpn-etree-01
Abstract
The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
Ethernet service known as Ethernet Tree (E-Tree). [ETREE-FMWK]
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
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This document is subject to BCP 78 and the IETF Trust's Legal
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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 . . . . . . . . . . 4
2.3 Scenario 3: Leaf AND Root site(s) per Ethernet Segment . . . 4
3 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . . . . 7
3.2 E-Tree without MAC Learning . . . . . . . . . . . . . . . . 7
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 . . . . . . . . . . . . . . . . . . . . . . . . 8
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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-FMWK] 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.
[E-VPN] 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 [KEYWORDS].
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
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
connected to the PE is uniquely identified as either a Root or a Leaf
site.
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+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+-----ES1----+--+ | | | MPLS | | | +--+----ES2-----+CE2|
+---+ (Root) | | E | | | /IP | | | E | | (Leaf) +---+
| | V | | | | | | V | |
| | I | | | | | | I | | +---+
| | | | | | | | +--+----ES3-----+CE3|
| +---+ | +------+ | +---+ | (Leaf) +---+
+---------+ +---------+
Figure 1: Scenario 1
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
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.
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+---------+ +---------+
| 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
3 Operation
[E-VPN] defines the notion of an Ethernet Segment which can be
readily used to identify a Root and/or Leaf site in E-TREE services.
In other words, [E-VPN] has inherent capability to support E-TREE
services without defining any new BGP routes and/or attributes. It
only requires a minor modification to the existing procedures as
shown in this section.
The following procedure is used consistently for all the scenarios
highlighted in the previous section. In order to apply the proper
egress filtering, which varies based on whether a packet is sent from
a Root or a Leaf, the MPLS-encapsulated frames MUST be tagged with an
indication of whether they originated from a Root or a Leaf Ethernet
Segment. 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 the split-
horizon rule defined in [E-VPN]:
- 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 encoding the Root or Leaf indication in the
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Flags field of the ESI MPLS label Extended Community attribute ([E-
VPN] Section 8) to indicate Root/Leaf status.
In the case where a multi-homed Ethernet Segment 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 the case where a
multi-homed Ethernet Segment has either Root or Leaf sites attached,
then a single ESI MPL label is allocated and advertised.
Furthermore, a PE advertises 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. Note that these special
labels are advertised on a per PE basis (i.e. each PE advertises only
two such special labels).
In addition to egress filtering (which is a MUST requirement), an E-
VPN PE implementation MAY provide topology constraint among the PEs
belonging to the same EVI associated with an E-TREE service. The
purpose of this topology constraint is to avoid having PEs with only
host Leaf sites importing and processing BGP MAC routes from each
other, thereby unnecessarily exhausting their RIB tables. However, as
soon as a Root site is added to a Leaf PE, then that PE needs to
process MAC routes from all other Leaf PEs and add them to its
forwarding table. To support such topology constrain in E-VPN, two
BGP Route-Targets (RTs) are used for 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. If for a given EVI, the PEs can
eventually have both Leaf and Root sites attached, even though they
may start as Root-only or Leaf-only PEs, then it is recommended to
use a single RT per EVI and avoid additional configuration and
operational overhead. If the number of EVIs is very large (e.g., more
than 32K or 64K), then RT type 0 as defined in [RFC4360] SHOULD be
used; otherwise, RT type 2 is sufficient.
Per [ETREE-FMWK], a generic E-Tree service supports all of the
following traffic flows:
- Ethernet Unicast from Root to Roots & Leaf
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- Ethernet Unicast from Leaf 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
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
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defined in [E-VPN], and the route import rules are as described in
previous sections.
4 Acknowledgement
We would like to thank Sami Boutros and Dennis Cai for their
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.
[RFC4360] S. Sangli et al, ""BGP Extended Communities Attribute",
February, 2006.
7.2 Informative References
[ETREE-FMWK] Key et al., "A Framework for E-Tree Service over MPLS
Network", draft-ietf-l2vpn-etree-frwk-01, work in progress, January
2012.
[E-VPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
l2vpn-evpn-01.txt, work in progress, February, 2012.
[ETREE-REQ] Key et al., "Requirements for MEF E-Tree Support in
L2VPN", draft-ietf-l2vpn-etree-reqt-03, work in progress, October
2012.
Authors' Addresses
Ali Sajassi
Cisco
Email: sajassi@cisco.com
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Samer Salam
Cisco
Email: ssalam@cisco.com
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.com
Jim Uttaro
AT&T
Email: ju1738@att.com
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