Hi Ravi,
Thanks for your comments. Please see my replies inline.
From: Ravi Singh <[email protected]<mailto:[email protected]>>
Date: Tuesday, August 15, 2017 at 11:56 PM
To: "[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Cc: "[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>,
"[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>,
"[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Subject: RtgDir review: draft-ietf-bess-evpn-etree-12
Resent-From: <[email protected]<mailto:[email protected]>>
Resent-To: Cisco Employee <[email protected]<mailto:[email protected]>>,
<[email protected]<mailto:[email protected]>>,
<[email protected]<mailto:[email protected]>>,
<[email protected]<mailto:[email protected]>>,
<[email protected]<mailto:[email protected]>>,
<[email protected]<mailto:[email protected]>>
Resent-Date: Tuesday, August 15, 2017 at 11:56 PM
Hello,
I have been selected as the Routing Directorate reviewer for this draft. The
Routing Directorate seeks to review all routing or routing-related drafts as
they pass through IETF last call and IESG review, and sometimes on special
request. The purpose of the review is to provide assistance to the Routing ADs.
For more information about the Routing Directorate, please see
http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir
Although these comments are primarily for the use of the Routing ADs, it would
be helpful if you could consider them along with any other IETF Last Call
comments that you receive, and strive to resolve them through discussion or by
updating the draft.
Document: draft-ietf-bess-evpn-etree-12
Reviewer: Ravi Singh
Review Date: 08/15/2017
Intended Status: Standards track
Summary: I have some concerns about this document that I think should be
resolved before publication.
I've reviewed this draft.
Most of my comments fall under the category of "minor comments" and "nits".
The only major comments pertain to
a. Sections 5.2/8.1: which appear like an overkill and could be
considered for dropping from text.
Section 3.3.1 describes the need and the use for composite tunnel type
described in 5.2/8.1. This has been discussed in length with your colleague
Eric Rosen, Jeffrey Zhang, and John Drake. After discussing with them, if you
still think it is “overkill”, then please elaborate as to why.
b. Need for a new section on the doc:
Include section to address this specifically: "Is (PBB-)EVPN being a *more
efficient* implementation of E-Tree functions demonstrated?" This is relevant
since the abstract makes a pitch for this draft addressing how PBB(-EVPN)
implement E-tree functionality more efficientlky. However, it takes a
fine-toothed comb to glean that info. Eg. First para in section 3.1. Nowhere
else in the text has the efficiency aspect been explicitly addressed. This
aspect could use a section of its own.
OK, the new section is 3.1 :-) It is not just the first paragraph of section
3.1 but the entire section that describes it - i.e., first paragraph says that
if filtering is done on the ingress PE, it provides an efficient filtering and
the rest of the section describes what it takes to do ingress filtering.
Feedback:
1. Abstract: very clear
2. Section1 : Introduction:
a. How about referring to "[RFC7432] is a solution for multipoint L2VPN
services" as EVPN more directly?
OK, changed it to "EVPN (RFC7432) is a solution …"
3. Section 2: E-tree scenarios
a. Section 2.1: for the sake of terminology clarification, please edit
the text to not mention the acronym until the full-expansion has been listed.
The draft does list the full-expansion. Just not before first using the acronym.
Done. Also added a new section to define acronyms/terminology.
b. Section 2.2: "
thus color MAC addresses via a "color" flag in a new extended community as
detailed in section 3.1." should be referring to section 5.1 instead.
Done. Thanks for the catch.
4. Section 3: Operation of EVPN
a. 3.1: "Extended Community with a Leaf indication flag is introduced
[section5.2]" ->
"Extended Community with a Leaf indication flag is introduced [section 5.1]"
Already corrected.
b. 3.3.1 (& section 5.2 as well): specifying (as this draft does) that the
ingress PE X acting for a root entity, be able to dictate to a PE Y acting on
behalf of a leaf entity, that PE Y should "ingress replication" or otherwise
sounds excessive. Also, this draft does not make a strong enough case for the
need for the modification to "PMSI Tunnel Attribute". Even if the foregoing was
ignored, the draft does not address how PE X behaves should PE Y choose not to
honor the setting of the "composite-tunnel bit".
Section 3.3.1 describes why ingress replication from leaf to roots would be
sufficient and how to signal it efficiently. The co-authors as well as other
reviewers (e.g., Eric Rosen, Jeffrey Zhang, and others listed in the ack
section) have consensus on the current description in section 3.3.1.
5. Section 4: Operation of PBB-EVPN: no specific comments. However, a
little more detail would be useful to avoid having the reader repeatedly refer
back to the PBB-EPVN RFC7623.
Both RFC 7432 and RFC7623 are prerequistes to this RFC and it is assumed the
reader has full knowledge of both.
6. Section 5: BGP encoding
a. This looks like an unexpected section given the "abstract" and the
"introduction" section.
The abstract and the introduction seem to indicate that no signaling changes
are needed to make (PBB-)EVPN provide E-tree services. Abstract/introduction
could use some rewording on this count.
Updated both abstract and introduction to say “a solution based on EVPN”
instead of “EVPN”.
b. Minor typo:
5.1: "The received PE" -> "The receiving PE"
Corrected it.
5.2: it would enhance readability if the flags were presented as
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|C |reserved |L|
+-+-+-+-+-+-+-+-+
C = composite-tunnel bit
C bit is in Tunnel Type field (and not the flag field).
Anyway, as stated above this draft does not make a strong enough case for the
need for the modification to "PMSI Tunnel Attribute". The value added by this
modification to the PMSI tunnel-attribute seems marginal. A leaf
7. Section 8: IANA considerations: it would be useful to include text
about the name of "E-Tree Flags" registry in section 5.1 and correlate these 2
sections.
Already addressed because of a similar comment (please refer to the attachment).
a. Section 8.1: could be considered for dropping, in view of the previous
comments on PMSI etc.
8. Appendix A: too wordy. Could do with fewer better-chosen words to
communicate the same message. Some minor singular/plural typos.
OK.
Thanks,
Ali
Regards
Ravi
BESS Workgroup A. Sajassi, Ed.
INTERNET-DRAFT S. Salam
Intended Status: Standards Track Cisco
Updates: 7385 J. Drake
Juniper
J. Uttaro
ATT
S. Boutros
VMware
J. Rabadan
Nokia
Expires: February 20, 2018 August 20, 2017
E-TREE Support in EVPN & PBB-EVPN
draft-ietf-bess-evpn-etree-13
Abstract
The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
Ethernet service known as Ethernet Tree (E-Tree). A solution
framework for supporting this service in MPLS networks is described
in RFC7387 ("A Framework for Ethernet Tree (E-Tree) Service over a
Multiprotocol Label Switching (MPLS) Network"). This document
discusses how those functional requirements can be met with a
solution based on Ethernet VPN (EVPN) [RFC7432] and how such solution
can offer a more efficient implementation of these functions. This
document makes use of the most significant bit of the PMSI tunnel
type governed by the IANA registry created by RFC7385, and hence
updates RFC7385 accordingly.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
Sajassi et al. Expires February 20, 2018 [Page 1]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Copyright and License Notice
Copyright (c) 2017 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
(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
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Specification of Requirements . . . . . . . . . . . . . . . 4
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
2 E-Tree Scenarios . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Scenario 1: Leaf OR Root site(s) per PE . . . . . . . . . . 5
2.2 Scenario 2: Leaf OR Root site(s) per AC . . . . . . . . . . 6
2.3 Scenario 3: Leaf OR Root site(s) per MAC . . . . . . . . . . 8
3 Operation for EVPN . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Known Unicast Traffic . . . . . . . . . . . . . . . . . . . 9
3.2 Broadcast, Unkonwn, and Multicast (BUM) Traffic . . . . . . 10
3.2.1 BUM traffic originated from a single-homed site on a
leaf AC . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.2 BUM traffic originated from a single-homed site on a
root AC . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2.3 BUM traffic originated from a multi-homed site on a
leaf AC . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2.4 BUM traffic originated from a multi-homed site on a
root AC . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3 E-TREE Traffic Flows for EVPN . . . . . . . . . . . . . . . 11
3.3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . . 12
3.3.2 E-Tree without MAC Learning . . . . . . . . . . . . . . 13
4 Operation for PBB-EVPN . . . . . . . . . . . . . . . . . . . . . 13
Sajassi et al. Expires February 20, 2018 [Page 2]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
4.1 Known Unicast Traffic . . . . . . . . . . . . . . . . . . . 14
4.2 Broadcast, Unkonwn, and Multicast (BUM) Traffic . . . . . . 14
4.3 E-Tree without MAC Learning . . . . . . . . . . . . . . . . 14
5 BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1 E-Tree Extended Community . . . . . . . . . . . . . . . . . 15
5.2 PMSI Tunnel Attribute . . . . . . . . . . . . . . . . . . . 16
6 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 17
7 Security Considerations . . . . . . . . . . . . . . . . . . . . 17
8 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 17
8.1 Considerations for PMSI Tunnel Types . . . . . . . . . . . . 18
9 References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1 Normative References . . . . . . . . . . . . . . . . . . . 18
9.2 Informative References . . . . . . . . . . . . . . . . . . 19
Appendix-A . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
Sajassi et al. Expires February 20, 2018 [Page 3]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
1 Introduction
The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
Ethernet service known as Ethernet Tree (E-Tree) [MEF6.1]. In an E-
Tree service, Attachment Circuits (ACs) are labeled as either Root or
Leaf ACs. Root ACs can communicate with all other ACs. Leaf ACs can
communicate with Root ACs but not with other Leaf ACs.
[RFC7387] describes 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 (RFC7432) 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. [RFC7623] combines the functionality of EVPN with
[802.1ah] Provider Backbone Bridging (PBB) for MAC address
scalability.
This document discusses how the functional requirements for E-Tree
service can be met with a solution based on (PBB-)EVPN and how such
solution can offer a more efficient implementation of these
functions. This document makes use of the most significant bit of the
PMSI tunnel type governed by the IANA registry created by RFC7385,
and hence updates RFC7385 accordingly. Section 2 discusses E-TREE
scenarios. Section 3 and 4 describe E-TREE solutions for EVPN and
PBB-EVPN respectively, and section 5 covers BGP encoding for E-TREE
solutions.
1.1 Specification of Requirements
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].
1.2 Terminology
Broadcast Domain: In a bridged network, the broadcast domain
corresponds to a Virtual LAN (VLAN), where a VLAN is typically
represented by a single VLAN ID (VID) but can be represented by
several VIDs where Shared VLAN Learning (SVL) is used per [802.1Q].
Bridge Table: An instantiation of a broadcast domain on a MAC-VRF.
CE: Customer Edge device, e.g., a host, router, or switch.
Sajassi et al. Expires February 20, 2018 [Page 4]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
EVI: An EVPN instance spanning the Provider Edge (PE) devices
participating in that EVPN.
MAC-VRF: A Virtual Routing and Forwarding table for Media Access
Control (MAC) addresses on a PE.
Ethernet Segment (ES): When a customer site (device or network) is
connected to one or more PEs via a set of Ethernet links, then that
set of links is referred to as an 'Ethernet segment'.
Ethernet Segment Identifier (ESI): A unique non-zero identifier that
identifies an Ethernet segment is called an 'Ethernet Segment
Identifier'.
Ethernet Tag: An Ethernet tag identifies a particular broadcast
domain, e.g., a VLAN. An EVPN instance consists of one or more
broadcast domains.
P2MP: Point to Multipoint.
PE: Provider Edge device.
2 E-Tree Scenarios
This document categorizes E-Tree scenarios into the following three
scenarios, depending on the nature of the Root/Leaf site association:
- Leaf OR Root site(s) per PE
- Leaf OR Root site(s) per Attachment Circuit (AC)
- Leaf OR Root site(s) per MAC
2.1 Scenario 1: Leaf OR Root site(s) per PE
In this scenario, a PE may receive traffic from either Root ACs OR
Leaf ACs for a given MAC-VRF/bridge table, but not both concurrently.
In other words, a given EVPN Instance (EVI) on a Provider Edge (PE)
device is either associated with root(s) or leaf(s). The PE may have
both Root and Leaf ACs albeit for different EVIs.
Sajassi et al. Expires February 20, 2018 [Page 5]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+---AC1----+--+ | | | MPLS | | | +--+----AC2-----+CE2|
+---+ (Root) | |MAC| | | /IP | | |MAC| | (Leaf) +---+
| |VRF| | | | | |VRF| |
| | | | | | | | | | +---+
| | | | | | | | +--+----AC3-----+CE3|
| +---+ | +------+ | +---+ | (Leaf) +---+
+---------+ +---------+
Figure 1: Scenario 1
In such scenario, using tailored BGP Route Target (RT) import/export
policies among the PEs belonging to the same EVI, can be used to
restrict the communications among Leaf PEs. To restrict the
communications among Leaf ACs connected to the same PE and belonging
to the same EVI, split-horizon filtering is used to block traffic
from one Leaf AC to another Leaf AC on a MAC-VRF for a given E-TREE
EVI. The purpose of this topology constraint is to avoid having PEs
with only Leaf sites importing and processing BGP MAC routes from
each other. 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 (Root ACs) and the other is associated
with the Leaf sites (Leaf ACs). 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.
2.2 Scenario 2: Leaf OR Root site(s) per AC
In this scenario, a PE can receive traffic from both Root ACs and
Leaf ACs for a given EVI. In other words, a given EVI on a PE can be
associated with both root(s) and leaf(s).
Sajassi et al. Expires February 20, 2018 [Page 6]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+-----AC1----+--+ | | | | | | +--+---AC2--+CE2|
+---+ (Leaf) | |MAC| | | MPLS | | |MAC| | (Leaf) +---+
| |VRF| | | /IP | | |VRF| |
| | | | | | | | | | +---+
| | | | | | | | +--+---AC3--+CE3|
| +---+ | +------+ | +---+ | (Root) +---+
+---------+ +---------+
Figure 2: Scenario 2
In this scenario, just like the previous scenario (in section 2.1),
two Route Targets (one for Root and another for Leaf) can be used.
However, the difference is that on a PE with both Root and Leaf ACs,
all remote MAC routes are imported and thus there needs to be a way
to differentiate remote MAC routes associated with Leaf ACs versus
the ones associated with Root ACs in order to apply the proper
ingress filtering.
In order to recognize the association of a destination MAC address to
a Leaf or Root AC and thus support ingress filtering on the ingress
PE with both Leaf and Root ACs, MAC addresses need to be colored with
Root or Leaf indication before advertisements to other PEs. There are
two approaches for such coloring:
A) To always use two RTs (one to designate Leaf RT and another for
Root RT)
B) To allow for a single RT be used per EVI just like [RFC7432] and
thus color MAC addresses via a "color" flag in a new extended
community as detailed in section 5.1.
Approach (A) would require the same data plane enhancements as
approach (B) if MAC-VRF/bridge tables used per broadcast domain
(e.g., VLAN), are to remain consistent with [RFC7432] (section 6). In
order to avoid data-plane enhancements for approach (A), multiple
bridge tables per VLAN may be considered; however, this has major
drawbacks as described in appendix-A and thus is not recommended.
Given that both approaches (A) and (B) would require exact same data-
plane enhancements, approach (B) is chosen here in order to allow for
RT usage consistent with baseline EVPN [RFC7432] and for better
generality. It should be noted that if one wants to use RT constrain
in order to avoid MAC advertisements associated with a Leaf AC to PEs
with only Leaf ACs, then two RTs (one for Root and another for Leaf)
can still be used with approach (B); however, in such applications
Sajassi et al. Expires February 20, 2018 [Page 7]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
Leaf/Root RTs will be used to constrain MAC advertisements and they
are not used to color the MAC routes for ingress filtering - i.e., in
approach (B), the coloring is always done via the new extended
community.
For this scenario, if for a given EVI, significant number of PEs have
both Leaf and Root sites attached, even though they may start as
Root-only or Leaf-only PEs, then a single RT per EVI should be used.
The reason for such recommendation is to alleviate the configuration
overhead associated with using two RTs per EVI at the expense of
having some unwanted MAC addresses on the Leaf-only PEs.
2.3 Scenario 3: Leaf OR Root site(s) per MAC
In this scenario, a PE may receive traffic from both Root AND Leaf
sites on a single Attachment Circuit (AC) of an EVI. This scenario is
not covered in both [RFC7387] and [MEF6.1]; however, it is covered in
this document for the sake of completeness. In this scenario, since
an AC carries traffic from both Root and Leaf sites, the granularity
at which Root or Leaf sites are identified is on a per MAC address.
This scenario is considered in this document for EVPN service with
only known unicast traffic because the Designated Forwarding (DF)
filtering per [RFC7432] would not be compatible with the required
egress filtering - i.e., Broadcast, Unknown, and Multicast (BUM)
traffic is not supported in this scenario and it is dropped by the
ingress PE.
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+-----AC1----+--+ | | | | | | +--+-----AC2----+CE2|
+---+ (Root) | | E | | | MPLS | | | E | | (Leaf/Root)+---+
| | V | | | /IP | | | V | |
| | I | | | | | | I | | +---+
| | | | | | | | +--+-----AC3----+CE3|
| +---+ | +------+ | +---+ | (Leaf) +---+
+---------+ +---------+
Figure 3: Scenario 3
3 Operation for EVPN
[RFC7432] defines the notion of Ethernet Segment Identifier (ESI)
Sajassi et al. Expires February 20, 2018 [Page 8]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
MPLS label used for split-horizon filtering of BUM traffic at the
egress PE. Such egress filtering capabilities can be leveraged in
provision of E-TREE services as seen shortly. In other words,
[RFC7432] has inherent capability to support E-TREE services without
defining any new BGP routes but by just defining a new BGP Extended
Community for leaf indication as shown later in this document
(section 5.1).
3.1 Known Unicast Traffic
Since in EVPN, MAC learning is performed in control plane via
advertisement of BGP routes, the filtering needed by E-TREE service
for known unicast traffic can be performed at the ingress PE, thus
providing very efficient filtering and avoiding sending known unicast
traffic over MPLS/IP core to be filtered at the egress PE as done in
traditional E-TREE solutions (e.g., E-TREE for VPLS [RFC7796]).
To provide such ingress filtering for known unicast traffic, a PE
MUST indicate to other PEs what kind of sites (root or leaf) its MAC
addresses are associated with by advertising a leaf indication flag
(via an Extended Community) along with each of its MAC/IP
Advertisement routes. The lack of such flag indicates that the MAC
address is associated with a root site. This scheme applies to all
scenarios described in section 2.
Tagging MAC addresses with a leaf indication enables remote PEs to
perform ingress filtering for known unicast traffic - i.e., 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 Leaf site or not. The ingress PE cross-
checks this flag with the status of the originating AC, and if both
are Leafs, then the packet is not forwarded.
In situation where MAC moves are allowed among Leaf and Root sites
(e.g., non-static MAC), PEs can receive multiple MAC/IP
advertisements routes for the same MAC address with different
Leaf/Root indications (and possibly different ESIs for multi-homing
scenarios). In such situations, MAC mobility procedures (section 15
of [RFC7432]) take precedence to first identify the location of the
MAC before associating that MAC with a Root or a Leaf site.
To support the above ingress filtering functionality, a new E-TREE
Extended Community with a Leaf indication flag is introduced [section
5.1]. This new Extended Community MUST be advertised with MAC/IP
Advertisement route. Besides MAC/IP Advertisement route, no other
EVPN routes are required to carry this new extended community.
Sajassi et al. Expires February 20, 2018 [Page 9]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
3.2 Broadcast, Unkonwn, and Multicast (BUM) Traffic
This specification does not provide support for filtering BUM
(Broadcast, Unknown, and Multicast) traffic on the ingress PE because
it is not possible to perform filtering of BUM traffic on the ingress
PE, as is the case with known unicast described above, due to the
multi-destination nature of BUM 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 Leaf AC or a
root AC, the MPLS-encapsulated frames MUST be tagged with an
indication that they originated from a Leaf AC - i.e., to be tagged
with a Leaf label as specified in section 5.1.
The Leaf label can be upstream assigned for P2MP LSP or downstream
assigned for ingress replication tunnels. The main difference between
downstream and upstream assigned Leaf label is that in case of
downstream assigned not all egress PE devices need to receive the
label just like ESI label for ingress replication procedures defined
in [RFC7432].
On the ingress PE, the PE needs to place all its Leaf ACs for a given
bridge domain in a single split-horizon group in order to prevent
intra-PE forwarding among its Leaf ACs. This intra-PE split-horizon
filtering applies to BUM traffic as well as known-unicast traffic.
There are four scenarios to consider as follows. In all these
scenarios, the ingress PE imposes the right MPLS label associated
with the originated Ethernet Segment (ES) depending on whether the
Ethernet frame originated from a Root or a Leaf site on that Ethernet
Segment (ESI label or Leaf label). The mechanism by which the PE
identifies whether a given frame originated from a Root or a Leaf
site on the segment is based on the AC identifier for that segment
(e.g., Ethernet Tag of the frame for 802.1Q frames). Other mechanisms
for identifying root or leaf (e.g., on a per MAC address basis) is
beyond the scope of this document.
3.2.1 BUM traffic originated from a single-homed site on a leaf AC
In this scenario, the ingress PE adds a Leaf label advertised using
the E-Tree Extended Community (Section 5.1) indicating a Leaf site.
This Leaf label, used for single-homing scenarios, is not on a per ES
basis but rather on a per PE basis - i.e., a single Leaf MPLS label
is used for all single-homed ES's on that PE. This Leaf label is
advertised to other PE devices, using the E-TREE Extended Community
(section 5.1) along with an Ethernet A-D per ES route with ESI of
zero and a set of Route Targets (RTs) corresponding to all EVIs on
the PE with at least one leaf site per EVI. The set of Ethernet A-D
per ES routes may be needed if the number of Route Targets (RTs) that
Sajassi et al. Expires February 20, 2018 [Page 10]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
need to be sent exceed the limit on a single route per [RFC7432]. The
ESI for the Ethernet A-D per ES route is set to zero to indicate
single-homed sites.
When a PE receives this special Leaf label in the data path, it
blocks the packet if the destination AC is of type Leaf; otherwise,
it forwards the packet.
3.2.2 BUM traffic originated from a single-homed site on a root AC
In this scenario, the ingress PE does not add any ESI label or Leaf
label and it operates per [RFC7432] procedures.
3.2.3 BUM traffic originated from a multi-homed site on a leaf AC
In this scenario, it is assumed that while different ACs (VLANs) on
the same ES could have different root/leaf designation (some being
roots and some being leafs), the same VLAN does have the same
root/leaf designation on all PEs on the same ES. Furthermore, it is
assumed that there is no forwarding among subnets - ie, the service
is EVPN L2 and not EVPN IRB [EVPN-IRB]. IRB use cases described in
[EVPN-IRB] are outside the scope of this document.
In such scenarios, If a multicast or broadcast packet is originated
from a leaf AC, then it only needs to carry Leaf label described in
section 3.2.1. This label is sufficient in providing the necessary
egress filtering of BUM traffic from getting sent to leaf ACs
including the leaf AC on the same Ethernet Segment.
3.2.4 BUM traffic originated from a multi-homed site on a root AC
In this scenario, both the ingress and egress PE devices follows the
procedure defined in [RFC7432] for adding and/or processing an ESI
MPLS label.
3.3 E-TREE Traffic Flows for EVPN
Per [RFC7387], a generic E-Tree service supports all of the following
traffic flows:
- Ethernet known unicast from Root to Roots & Leaf
- Ethernet known unicast from Leaf to Root
- Ethernet BUM traffic from Root to Roots & Leafs
- Ethernet BUM traffic 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
Sajassi et al. Expires February 20, 2018 [Page 11]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
application. In the case where unicast flows need not be supported,
the L2VPN PEs can avoid performing any MAC learning function.
The following subsections 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
unicast traffic flows must be supported among Root and Leaf sites. In
this case, the PE(s) with Root sites performs MAC learning in the
data-path over the Ethernet Segments, and advertises reachability in
EVPN MAC/IP Advertisement Routes. These routes will be imported by
all PEs for that EVI (i.e., PEs that have Leaf sites as well as PEs
that have Root sites). Similarly, the PEs with Leaf sites perform MAC
learning in the data-path over their Ethernet Segments, and advertise
reachability in EVPN MAC/IP Advertisement Routes. For the scenario
described in section 2.1 (or possibly section 2.2), these routes are
imported only by PEs with at least one Root site in the EVI - i.e., 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 per
[RFC7432].
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 (section 16 of [RFC7432]). The multicast tunnels are set
up through the exchange of the EVPN Inclusive Multicast route, as
defined in [RFC7432].
To support multicast/broadcast from Leaf to Root sites, ingress
replication should be sufficient for most scenarios where there are
only a few Roots (typically two). Therefore, in a typical scenario, a
root PE needs to support both a P2MP tunnel in transmit direction
from itself to leaf PEs and at the same time it needs to support
ingress-replication tunnels in receive direction from leaf PEs to
itself. In order to signal this efficiently from the root PE, a new
composite tunnel type is defined per section 5.2. This new composite
tunnel type is advertised by the root PE to simultaneously indicate a
P2MP tunnel in transmit direction and an ingress-replication tunnel
in the receive direction for the BUM traffic.
If the number of Roots is large, P2MP tunnels originated at the PEs
with Leaf sites may be used and thus there will be no need to use the
modified PMSI tunnel attribute in section 5.2 for composite tunnel
type.
Sajassi et al. Expires February 20, 2018 [Page 12]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
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 mainly
multicast or broadcast. In this case, the PEs do not exchange EVPN
MAC/IP Advertisement Routes. Instead, the Inclusive Multicast
Ethernet Tag route is used to support BUM traffic.
The fields of this route are populated per the procedures defined in
[RFC7432], and the multicast tunnel setup criteria are as described
in the previous section.
Just as in the previous section, if the number of PEs with root sites
are only a few and thus ingress replication is desired from leaf PEs
to these root PEs, then the modified PMSI attribute as defined in
section 5.2 should be used.
4 Operation for PBB-EVPN
In PBB-EVPN, the PE advertises a Root/Leaf indication along with each
B-MAC Advertisement route, to indicate whether the associated B-MAC
address corresponds to a Root or a Leaf site. Just like the EVPN
case, the new E-TREE Extended Community defined in section [5.1] is
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 advertised: one B-MAC
address is per ES as specified in [RFC7623] and implicitly denoting
Root, and the other B-MAC address is per PE and explicitly denoting
Leaf. The former B-MAC address is not advertised with the E-TREE
extended community but the latter B-MAC denoting Leaf is advertised
with the new E-TREE extended community where "Leaf-indication" flag
is set. In such multi-homing scenarios where an Ethernet Segment has
both Root and Leaf ACs, it is assumed that While different ACs
(VLANs) on the same ES could have different root/leaf designation
(some being roots and some being leafs), the same VLAN does have the
same root/leaf designation on all PEs on the same ES. Furthermore, it
is assumed that there is no forwarding among subnets - ie, the
service is L2 and not IRB. IRB use case is outside the scope of this
document.
The ingress PE uses the right B-MAC source address depending on
whether the Ethernet frame originated from the Root or Leaf AC 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.
Sajassi et al. Expires February 20, 2018 [Page 13]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
Furthermore, a PE advertises two special global B-MAC addresses: one
for Root and another for Leaf, and tags the Leaf one as such in the
MAC Advertisement route. These B-MAC addresses are used as source
addresses for traffic originating from single-homed segments. The B-
MAC address used for indicating Leaf sites can be the same for both
single-homed and multi-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.
4.2 Broadcast, Unkonwn, and Multicast (BUM) Traffic
For BUM traffic, the PEs must perform egress filtering. When a PE
receives a MAC advertisement route (which will be used as a source B-
MAC for BUM traffic), it updates its egress filtering (based on the
source B-MAC 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 its B-MAC list used for egress
filtering - i.e., to block traffic from that B-MAC address.
- 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 [RFC7623] and
does not require any additional flags in the data-plane.
Just as in section 3.2, 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 as known-unicast traffic.
4.3 E-Tree without MAC Learning
In scenarios where the traffic of interest is only Multicast and/or
broadcast, the PEs implementing an E-Tree service do not need to do
any MAC learning. In such scenarios the filtering must be performed
on egress PEs. For PBB-EVPN, the handling of such traffic is per
Sajassi et al. Expires February 20, 2018 [Page 14]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
section 4.2 without C-MAC learning part of it at both ingress and
egress PEs.
5 BGP Encoding
This document defines a new BGP Extended Community for EVPN.
5.1 E-Tree Extended Community
This Extended Community is a new transitive Extended Community
[RFC4360] having a Type field value of 0x06 (EVPN) and the Sub-Type
0x05. It is used for leaf indication of known unicast and BUM
traffic.
The E-TREE Extended Community is encoded as an 8-octet value as
follows:
0 1 2 3
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=0x06 | Sub-Type=0x05 | Flags(1 Octet)| Reserved=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved=0 | Leaf Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: E-TREE Extended Community
The Flags field has the following format:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |L| (MBZ = Must Be Zero)
+-+-+-+-+-+-+-+-+
This document defines the following flags:
+ Leaf-Indication (L)
A value of one indicates a Leaf AC/Site. The rest of flag bits are
reserved and should be set to zero.
When this Extended Community (EC) is advertised along with MAC/IP
Advertisement route (for known unicast traffic) per section 3.1, the
Leaf-Indication flag MUST be set to one and Leaf Label SHOULD be set
to zero. The label value is encoded in the high-order 20 bits of the
Sajassi et al. Expires February 20, 2018 [Page 15]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
Leaf Label field. The receiving PE SHOULD ignore Leaf Label and only
processes Leaf-Indication flag. A value of zero for Leaf-Indication
flag is invalid when sent along with MAC/IP advertisement route and
an error should be logged.
When this EC is advertised along with Ethernet A-D per ES route (with
ESI of zero) for BUM traffic to enable egress filtering on
disposition PEs per sections 3.2.1 and 3.2.3, the Leaf Label MUST be
set to a valid MPLS label (i.e., non-reserved assigned MPLS label
[RFC3032]) and the Leaf-Indication flag SHOULD be set to zero. The
receiving PE SHOULD ignore the Leaf-Indication flag. A non-valid MPLS
label when sent along with the Ethernet A-D per ES route, should be
ignored and logged as an error.
The reserved bits SHOULD be set to zero by the transmitter and SHOULD
be ignored by the receiver.
5.2 PMSI Tunnel Attribute
[RFC6514] defines PMSI Tunnel attribute which is an optional
transitive attribute with the following format:
+---------------------------------+
| Flags (1 octet) |
+---------------------------------+
| Tunnel Type (1 octets) |
+---------------------------------+
| MPLS Label (3 octets) |
+---------------------------------+
| Tunnel Identifier (variable) |
+---------------------------------+
Figure 5: PMSI Tunnel Attribute
This document defines a new Composite tunnel type by introducing a
new 'Composite Tunnel' bit in the Tunnel Type field and adding a MPLS
label to the Tunnel Identifier field of PMSI Tunnel attribute as
detailed below. This document uses all other remaining fields per
existing definition. Composite tunnel type is advertised by the root
PE to simultaneously indicate a non-ingress replication tunnel (e.g.,
P2MP tunnel) in transmit direction and an ingress-replication tunnel
in the receive direction for the BUM traffic.
When receiver ingress-replication label is needed, the high-order bit
of the tunnel type field (Composite Tunnel bit) is set while the
remaining low-order seven bits indicate the tunnel type as before
Sajassi et al. Expires February 20, 2018 [Page 16]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
(for the existing tunnel types). When this Composite Tunnel bit is
set, the "tunnel identifier" field would begin with a three-octet
label, followed by the actual tunnel identifier for the transmit
tunnel. PEs that don't understand the new meaning of the high-order
bit would treat the tunnel type as an undefined tunnel type and would
treat the PMSI tunnel attribute as a malformed attribute [RFC6514].
For the PEs that do understand the new meaning of the high-order, if
ingress replication is desired when sending BUM traffic, the PE will
use the the label in the Tunnel Identifier field when sending its BUM
traffic.
Using the Composite Tunnel bit for Tunnel Types 0x00 'no tunnel
information present' and 0x06 'Ingress Replication' is invalid, and a
PE that receives a PMSI Tunnel attribute with such information,
considers it as malformed and it SHOULD treat this Update as though
all the routes contained in this Update had been withdrawn per
section 5 of [RFC6514].
6 Acknowledgement
We would like to thank Eric Rosen, Jeffrey Zhang, Dennis Cai, and
Antoni Przygienda for their valuable comments. The authors would also
like to thank Thomas Morin for shepherding this document and
providing valuable comments.
7 Security Considerations
Since this document uses the EVPN constructs of [RFC7432] and
[RFC7623], the same security considerations in these documents are
also applicable here. Furthermore, this document provides additional
security check by allowing sites (or ACs) of an EVPN instance to be
designated as "Root" or "Leaf" and preventing any traffic exchange
among "Leaf" sites of that VPN through ingress filtering for known
unicast traffic and egress filtering for BUM traffic.
8 IANA Considerations
IANA has allocated value 5 in the "EVPN Extended Community Sub-Types"
registry defined in [RFC7153] as follow:
SUB-TYPE VALUE NAME Reference
0x05 E-TREE Extended Community This document
This document creates a one-octet registry called "E-Tree Flags".
Sajassi et al. Expires February 20, 2018 [Page 17]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
New registrations will be made through the "RFC Required" procedure
defined in [RFC5226]. Initial registrations are as follows:
bit Name Reference
0-6 Unassigned
7 Leaf-Indication This document
8.1 Considerations for PMSI Tunnel Types
The "P-Multicast Service Interface Tunnel (PMSI Tunnel) Tunnel Types"
registry in the "Border Gateway Protocol (BGP) Parameters" registry
needs to be updated to reflect the use of the most significant bit as
"Composite Tunnel" bit (section 5.2).
For this purpose, this document updates [RFC7385].
The registry is to be updated, by removing the entries for 0xFB-0xFE
and 0x0F, and replacing them by:
Value Meaning Reference
0x0C-0x7A Unassigned
0x7B-0x7E Experimental this document
0x7F Reserved this document
0x80-0xFA Reserved for Composite tunnel this document
0xFB-0xFE Experimental [RFC7385]
0xFF Reserved [RFC7385]
The allocation policy for values 0x00 to 0x7A is IETF Review
[RFC5226]. The range for experimental use is now 0x7B-0x7E, and value
in this range are not to be assigned. The status of 0x7F may only be
changed through Standards Action [RFC5226].
9 References
9.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC8126] Cotton et al, "Guidelines for Writing an IANA
Considerations Section in RFCs", June, 2017.
[RFC7387] Key et al., "A Framework for E-Tree Service over MPLS
Sajassi et al. Expires February 20, 2018 [Page 18]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
Network", October 2014.
[MEF6.1] Metro Ethernet Forum, "Ethernet Services Definitions - Phase
2", MEF 6.1, April 2008.
[RFC7432] Sajassi et al., "BGP MPLS Based Ethernet VPN", February,
2015.
[RFC7623] Sajassi et al., "Provider Backbone Bridging Combined with
Ethernet VPN (PBB-EVPN)", September, 2015.
[RFC7385] Andersson et al., "IANA Registry for P-Multicast Service
Interface (PMSI) Tunnel Type Code Points", October, 2014.
[RFC7153] Rosen et al., "IANA Registries for BGP Extended
Communities", March, 2014.
[RFC6514] Aggarwal et al., "BGP Encodings and Procedures for
Multicast in MPLS/BGP IP VPNs", February, 2012.
[RFC4360] Sangli et al., "BGP Extended Communities Attribute",
February, 2006.
9.2 Informative References
[RFC4360] S. Sangli et al, "BGP Extended Communities Attribute",
February, 2006.
[RFC3032] E. Rosen et al, "MPLS Label Stack Encoding", January 2001.
[RFC7796] Y. Jiang et al, "Ethernet-Tree (E-Tree) Support in Virtual
Private LAN Service (VPLS)", March 2016.
[EVPN-IRB] A. Sajassi et al, "Integrated Routing and Bridging in
EVPN", draft-ietf-bess-evpn-inter-subnet-forwarding-03, February 8,
2017.
Appendix-A
When two MAC-VRFs (two bridge tables per VLANs) are used for an E-
TREE service (one for root ACs and another for Leaf ACs) on a given
PE, then the following complications in data-plane path can result.
Maintaining two MAC-VRFs (two bridge tables) per VLAN (when both Leaf
and Root ACs exists for that VLAN) would either require two lookups
be performed per MAC address in each direction in case of a miss, or
duplicating many MAC addresses between the two bridge tables
Sajassi et al. Expires February 20, 2018 [Page 19]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
belonging to the same VLAN (same E-TREE instance). Unless two lookups
are made, duplication of MAC addresses would be needed for both
locally learned and remotely learned MAC addresses. Locally learned
MAC addresses from Leaf ACs need to be duplicated onto Root bridge
table and locally learned MAC addresses from Root ACs need to be
duplicated onto Leaf bridge table. Remotely learned MAC addresses
from Root ACs need to be copied onto both Root and Leaf bridge
tables. Because of potential inefficiencies associated with data-
plane implementation of additional MAC lookup or duplication of MAC
entries, this option is not believed to be implementable without
dataplane performance inefficiencies in some platforms and thus this
document introduces the coloring as described in section 2.2 and
detailed in section 3.1.
Contributors
In addition to the authors listed on the front page, the following
co-authors have also contributed to this document:
Wim Henderickx
Nokia
Aldrin Isaac
Wen Lin
Juniper
Authors' Addresses
Ali Sajassi
Cisco
Email: [email protected]
Samer Salam
Cisco
Email: [email protected]
John Drake
Juniper
Email: [email protected]
Jim Uttaro
AT&T
Sajassi et al. Expires February 20, 2018 [Page 20]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 22, 2017
Email: [email protected]
Sami Boutros
VMware
Email: [email protected]
Jorge Rabadan
Nokia
Email: [email protected]
Sajassi et al. Expires February 20, 2018 [Page 21]
_______________________________________________
BESS mailing list
[email protected]
https://www.ietf.org/mailman/listinfo/bess
