Internet DRAFT - draft-sajassi-bess-evpn-etree
draft-sajassi-bess-evpn-etree
L2VPN Workgroup Ali Sajassi
INTERNET-DRAFT Samer Salam
Intended Status: Standards Track Sami Boutros
Cisco
Wim Henderickx Jim Uttaro
Jorge Rabadan AT&T
Alcatel-Lucent
Aldrin Isaac
Bloomberg
Expires: April 27, 2015 October 27, 2014
E-TREE Support in EVPN & PBB-EVPN
draft-sajassi-bess-evpn-etree-00
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 EVPN.
Status of this Memo
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Copyright and License Notice
Copyright (c) 2013 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
Provisions Relating to IETF Documents
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described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2 E-Tree Scenarios and EVPN / PBB-EVPN 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 for EVPN . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 Known Unicast Traffic . . . . . . . . . . . . . . . . . . . 5
3.2 BUM Traffic . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3 E-TREE Traffic Flows for EVPN . . . . . . . . . . . . . . . 7
3.3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . . 7
3.3.2 E-Tree without MAC Learning . . . . . . . . . . . . . . 8
4 Operation for PBB-EVPN . . . . . . . . . . . . . . . . . . . . . 8
4.1 Known Unicast Traffic . . . . . . . . . . . . . . . . . . . 9
4.2 BUM Traffic . . . . . . . . . . . . . . . . . . . . . . . . 9
5 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 10
6 Security Considerations . . . . . . . . . . . . . . . . . . . . 10
7 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10
8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1 Normative References . . . . . . . . . . . . . . . . . . . 10
8.2 Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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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.
[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. [PBB-
EVPN] combines the functionality of EVPN with [802.1ah] Provider
Backbone Bridging for MAC address scalability.
This document discusses how the functional requirements for E-Tree
service can be easily met with EVPN and PBB-EVPN.
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 EVPN / PBB-EVPN 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
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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
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 for EVPN
[EVPN] 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, [EVPN] has inherent capability to support E-TREE services
without defining any new BGP routes. It only requires a minor
modification to the existing procedures and a modification to a BGP
attribute as shown in this section.
The following procedures are used consistently for all the scenarios
highlighted in the previous section.
3.1 Known Unicast Traffic
For known unicast traffic, the PE must advertise a Root/Leaf
indication along with each MAC Advertisement route, to indicate
whether the associated MAC address was learnt from a Root or a Leaf.
This enables remote PEs to perform ingress filtering for known
unicast traffic: On the ingress PE, the MAC destination address
lookup yields, in addition to the forwarding adjacency, a flag which
indicates whether the target MAC is associated with a Root or a Leaf
site. The ingress PE cross-checks this flag with the status of the
originating site, and if both are a Leaf, then the packet is not
forwarded.
The PE places all Leaf Ethernet Segments of a given bridge domain in
a single split-horizon group in order to prevent intra-PE forwarding
among Leaf segments. This split-horizon function applies to BUM
traffic as well.
To support the above ingress filtering functionality, a new Root/Leaf
indication flag will added to the Tunnel Encapsulation Type Extended
Community [RFC5512]. This extended community will be advertised with
each EVPN MAC Advertisement route.
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3.2 BUM Traffic
For BUM traffic, it is not possible to perform filtering on the
ingress PE, as is the case with known unicast, because of the multi-
destination nature of the traffic. As such, the solution relies on
egress filtering. 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 EVPN through the use of the ESI MPLS label, since
this label identifies the Ethernet Segment of origin of a given
frame. The egress PE determines whether or not to forward a
particular frame to an Ethernet Segment depending on the split-
horizon rule defined in [EVPN]:
- 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
Flags field of the ESI MPLS label Extended Community attribute
([EVPN] 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 based on the Ethernet Tag associated with the frame. Other
mechanisms of identification, beyond the Ethernet Tag, are outside
the scope of this document. It should be noted that support for both
Root and Leaf sites on a single Ethernet Segment requires that the PE
performs the Ethernet Segment split-horizon check on a per Ethernet
Tag basis. 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
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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
EVPN 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 EVPN, two BGP
Route-Targets (RTs) are used for every EVPN 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.
3.3 E-TREE Traffic Flows for EVPN
Per [ETREE-FMWK], a generic E-Tree service supports all of the
following traffic flows:
- Ethernet Unicast from Root to Roots & Leaf
- 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
EVPN to support E-Tree service with and without MAC learning.
3.3.1 E-Tree with MAC Learning
The PEs implementing an E-Tree service must perform MAC learning when
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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 EVPN 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 EVPN 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 EVPN Inclusive Multicast route, as defined in [EVPN].
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.
3.3.2 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 EVPN MAC
Advertisement routes. Instead, the Ethernet A-D routes are used to
exchange the EVPN labels.
The fields of the Ethernet A-D route are populated per the procedures
defined in [EVPN], and the route import rules are as described in
previous sections.
4 Operation for PBB-EVPN
In PBB-EVPN, the PE must advertise a Root/Leaf indication along with
each MAC Advertisement route, to indicate whether the associated B-
MAC address corresponds to a Root or a Leaf site. Similar to the EVPN
case, this flag will be added to the Tunnel Encapsulation Type
Extended Community [RFC5512], and advertised with each MAC
Advertisement route.
In the case where a multi-homed Ethernet Segment has both Root and
Leaf sites attached, two B-MAC addresses are allocated and
advertised: one B-MAC address denotes Root and the other denotes
Leaf. The ingress PE uses the right B-MAC source address depending on
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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 based on the Ethernet Tag associated with the frame. Other
mechanisms of identification, beyond the Ethernet Tag, are outside
the scope of this document. It should be noted that support for both
Root and Leaf sites on a single Ethernet Segment requires that the PE
performs the Ethernet Segment split-horizon check on a per Ethernet
Tag basis. In the case where a multi-homed Ethernet Segment has
either Root or Leaf sites attached, then a single B-MAC address is
allocated and advertised per segment.
Furthermore, a PE advertises two global B-MAC addresses: one for Root
and another for Leaf, and tags them as such in the MAC Advertisement
routes. These B-MAC addresses are used as source addresses for
traffic originating from single-homed segments.
4.1 Known Unicast Traffic
For known unicast traffic, the PEs perform ingress filtering: On the
ingress PE, the C-MAC destination address lookup yields, in addition
to the target B-MAC address and forwarding adjacency, a flag which
indicates whether the target B-MAC is associated with a Root or a
Leaf site. The ingress PE cross-checks this flag with the status of
the originating site, and if both are a Leaf, then the packet is not
forwarded.
The PE places all Leaf Ethernet Segments of a given bridge domain in
a single split-horizon group in order to prevent intra-PE forwarding
among Leaf segments. This split-horizon function applies to BUM
traffic as well.
4.2 BUM Traffic
For BUM traffic, the PEs must perform egress filtering. When a PE
receives a MAC advertisement route, it updates its Ethernet Segment
egress filtering function (based on the B-MAC source address), as
follows:
- If the MAC Advertisement route indicates that the advertised B-MAC
is a Leaf, and the local Ethernet Segment is a Leaf as well, then the
source B-MAC address is added to the B-MAC filtering list.
- Otherwise, the B-MAC filtering list is not updated.
When the egress PE receives the packet, it examines the B-MAC source
address to check whether it should filter or forward the frame. Note
that this uses the same filtering logic as baseline [PBB-EVPN] and
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does not require any additional flags in the data-plane.
5 Acknowledgement
We would like to thank Sami Boutros and Dennis Cai for their
comments.
6 Security Considerations
Same security considerations as [EVPN].
7 IANA Considerations
Allocation of Extended Community Type and Sub-Type for EVPN.
8 References
8.1 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.
[RFC5512] Mohapatra, P. and E. Rosen, "The BGP
Encapsulation Subsequent Address Family Identifier (SAFI)
and the BGP Tunnel Encapsulation Attribute", RFC 5512,
April 2009.
8.2 Informative References
[ETREE-FMWK] Key et al., "A Framework for E-Tree Service over MPLS
Network", draft-ietf-l2vpn-etree-frwk-03, work in progress, September
2013.
[EVPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
l2vpn-evpn-04.txt, work in progress, July, 2013.
[PBB-EVPN] Sajassi et al., "PBB-EVPN", draft-ietf-l2vpn-pbb-evpn-
05.txt, work in progress, October, 2013.
Authors' Addresses
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Ali Sajassi
Cisco
Email: sajassi@cisco.com
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
Aldrin
Bloomberg Issac
Email: aisaac71@bloomberg.net
Sami Boutros
Cisco
Email: sboutros@cisco.com
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