BESS Workgroup J. Rabadan, Ed.
Internet Draft J. Kotalwar
S. Sathappan
Intended status: Standards Track Nokia
E. Rosen
Z. Zhang
W. Lin
Juniper
Expires: April 25, 2019 October 22, 2018
Multicast Source Redundancy in EVPN Networks
draft-skr-bess-evpn-redundant-mcast-source-00
Abstract
EVPN supports intra and inter-subnet IP multicast forwarding.
However, EVPN (or conventional IP multicast techniques for that
matter) do not have a solution for the case where a given multicast
group carries more than one flow (i.e., more than one source), but
where it is desired that each receiver gets only one of the several
flows. Existing multicast techniques assume there are no redundant
sources sending the same flows to the same IP multicast group, and,
in case there were redundant sources, the receiver's application
would deal with the received duplicated packets. This document
extends the existing EVPN specifications and assumes that IP
Multicast source redundancy may exist. It also assumes that, in case
two or more sources send the same IP Multicast flows into the tenant
domain, the EVPN PEs need to avoid that the receivers get packet
duplication by following the described procedures.
Status of this Memo
This Internet-Draft is submitted 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.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on April 25, 2019.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Background on IP Multicast Delivery in EVPN Networks . . . . 6
1.2.1 Intra-subnet IP Multicast Forwarding . . . . . . . . . . 6
1.2.2 Inter-subnet IP Multicast Forwarding . . . . . . . . . . 7
1.3 Multi-Homed IP Multicast Sources in EVPN . . . . . . . . . . 9
1.4 The Need for Redundant IP Multicast Sources in EVPN . . . . 11
2. Solution Overview . . . . . . . . . . . . . . . . . . . . . . . 11
3. BGP EVPN Extensions . . . . . . . . . . . . . . . . . . . . . . 13
4. Warm Standby (WS) Solution for Redundant G-Sources . . . . . . 14
4.1 WS Example in an OISM Network . . . . . . . . . . . . . . . 15
4.2 WS Example in a Single-BD Tenant Network . . . . . . . . . . 17
5. Hot Standby (HS) Solution for Redundant G-Sources . . . . . . . 18
5.1 Use of BFD in the HS Solution . . . . . . . . . . . . . . . 21
5.2 HS Example in an OISM Network . . . . . . . . . . . . . . . 21
5.3 HS Example in a Single-BD Tenant Network . . . . . . . . . . 25
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6. Security Considerations . . . . . . . . . . . . . . . . . . . . 26
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 26
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.1. Normative References . . . . . . . . . . . . . . . . . . . 26
8.2. Informative References . . . . . . . . . . . . . . . . . . 27
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 27
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
Intra and Inter-subnet IP Multicast forwarding are supported in EVPN
networks. [IGMP-PROXY] describes the procedures required to optimize
the delivery of IP Multicast flows when Sources and Receivers are
connected to the same EVPN BD (Broadcast Domain), whereas [OISM]
specifies the procedures to support Inter-subnet IP Multicast in a
tenant network. Inter-subnet IP Multicast means that IP Multicast
Source and Receivers of the same multicast flow are connected to
different BDs of the same tenant.
[IGMP-PROXY], [OISM] or conventional IP multicast techniques do not
have a solution for the case where a given multicast group carries
more than one flow (i.e., more than one source), but where it is
desired that each receiver gets only one of the several flows.
Multicast techniques assume there are no redundant sources sending
the same flows to the same IP multicast group, and, in case there
were redundant sources, the receiver's application would deal with
the received duplicated packets.
As a workaround in conventional IP multicast (PIM or MVPN networks),
if all the redundant sources are given the same IP address, each
receiver will get only one flow. The reason is that, in conventional
IP multicast, (S,G) state is always created. It is always created by
the RP, and sometimes by the Last Hop Router (LHR). The (S,G) state
always binds the (S,G) flow to a source-specific tree, rooted at the
source IP address. If multiple sources have the same IP address, one
may end up with multiple (S,G) trees. However, the way the trees are
constructed ensures that any given LHR or RP is on at most one of
them. The use of an anycast address assigned to multiple sources may
be useful for warm standby redundancy solutions. However, on one
hand, it's not really helpful for hot standby redundancy solutions
and on the other hand, configuring the same IP address (in particular
IPv4 address) in multiple sources may bring issues if the sources
need to be reached by IP unicast traffic or if the sources are
attached to the same Broadcast Domain.
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In addition, in the scenario where several G-sources are attached via
EVPN/OISM, there is not necessarily any (S,G) state created for the
redundant sources. In general, the LHRs have only (*,G) state, and
there may not be an RP (creating (S,G) state) either. Therefore, this
document extends the above two specifications and assumes that IP
Multicast source redundancy may exist. It also assumes that, in case
two or more sources send the same IP Multicast flows into the tenant
domain, the EVPN PEs need to avoid that the receivers get packet
duplication.
The solution provides support for Warm Standby (WS) and Hot Standby
(HS) redundancy. WS is defined as the redundancy scenario in which
the upstream PEs attached to the redundant sources of the same
tenant, make sure that only one source of the same flow can send
multicast to the interested downstream PEs at the same time. In HS
the upstream PEs forward the redundant multicast flows to the
downstream PEs, and the downstream PEs make sure only one flow is
forwarded to the interested attached receivers.
1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
o OISM: Optimized Inter-Subnet Multicast, as in [OISM].
o Broadcast Domain (BD): an emulated ethernet, such that two systems
on the same BD will receive each other's link-local broadcasts. In
this document, BD also refers to the instantiation of a Broadcast
Domain on an EVPN PE. An EVPN PE can be attached to one or multiple
BDs of the same tenant.
o Designated Forwarder (DF): as defined in [RFC7432], an ethernet
segment may be multi-homed (attached to more than one PE). An
ethernet segment may also contain multiple BDs, of one or more
EVIs. For each such EVI, one of the PEs attached to the segment
becomes that EVI's DF for that segment. Since a BD may belong to
only one EVI, we can speak unambiguously of the BD's DF for a given
segment.
o Upstream PE: in this document an Upstream PE is referred to as the
EVPN PE that is connected to the IP Multicast source or closest to
it. It receives the IP Multicast flows on local ACs (Attachment
Circuits).
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o Downstream PE: in this document a Downstream PE is referred to as
the EVPN PE that is connected to the IP Multicast receivers and
gets the IP Multicast flows from remote EVPN PEs.
o G-traffic: any frame with an IP payload whose IP Destination
Address (IP DA) is a multicast group G.
o G-source: any system sourcing traffic to G.
o SFG: Single Flow Group, i.e., a multicast group address G which
represents traffic that contains only a single flow. However,
multiple sources - with the same or different IP - may be
transmitting an SFG.
o Redundant G-source: a host or router that transmits an SFG in a
tenant network where there are more hosts or routers transmitting
the same SFG. Redundant G-sources for the same SFG SHOULD have
different IP addresses when in the same BD, and MAY have the same
IP address when in different BDs of the same tenant network.
Redundant G-sources are assumed NOT to be "bursty" in this document
(typical example are Broadcast TV G-sources or similar).
o P-tunnel: Provider tunnel refers to the type of tree a given
upstream EVPN PE uses to forward multicast traffic to downstream
PEs. Examples of P-tunnels supported in this document are Ingress
Replication (IR), Assisted Replication (AR), BIER, mLDP or P2MP
RSVP-TE.
o Inclusive Multicast Tree or Inclusive Provider Multicast Service
Interface (I-PMSI): defined in [RFC6513], in this document it is
applicable only to EVPN and refers to the default multicast tree
for a given BD. All the EVPN PEs that are attached to a specific BD
belong to the I-PMSI for the BD. The I-PMSI trees are signaled by
EVPN Inclusive Multicast Ethernet Tag (IMET) routes.
o Selective Multicast Tree or Selective Provider Multicast Service
Interface (S-PMSI): defined in [RFC6513], in this document it is
applicable only to EVPN and refers to the multicast tree to which
only the interested PEs of a given BD belong to. There are two
types of EVPN S-PMSIs:
- EVPN S-PMSIs that require the advertisement of S-PMSI AD routes
from the upstream PE, as in [EVPN-BUM]. The interested downstream
PEs join the S-PMSI tree as in [EVPN-BUM].
- EVPN S-PMSIs that don't require the advertisement of S-PMSI AD
routes. They use the forwarding information of the IMET routes,
but upstream PEs send IP Multicast flows only to downstream PEs
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issuing Selective Multicast Ethernet Tag (SMET) routes for the
flow. These S-PMSIs are only supported with the following P-
tunnels: Ingress Replication (IR), Assisted Replication (AR) and
BIER.
This document also assumes familiarity with the terminology of
[RFC7432], [RFC4364], [RFC6513], [RFC6514], [IGMP-PROXY], [OISM],
[EVPN-RT5] and [EVPN-BUM].
1.2 Background on IP Multicast Delivery in EVPN Networks
IP Multicast is all about forwarding a single copy of a packet from a
source S to a group of receivers G along a multicast tree. That
multicast tree can be created in an EVPN tenant domain where S and
the receivers for G are connected to the same BD or different BD. In
the former case, we refer to Intra-subnet IP Multicast forwarding,
whereas the latter case will be referred to as Inter-subnet IP
Multicast forwarding.
1.2.1 Intra-subnet IP Multicast Forwarding
When the source S1 and receivers interested in G1 are attached to the
same BD, the EVPN network can deliver the IP Multicast traffic to the
receivers in two different ways (Figure 1):
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S1 + S1 +
(a) + | (b) + |
| | (S1,G1) | | (S1,G1)
PE1 | | PE1 | |
+-----+ v +-----+ v
|+---+| |+---+|
||BD1|| ||BD1||
|+---+| |+---+|
+-----+ +-----+
+-------|-------+ +-------|
| | | | |
v v v v v
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
|+---+| |-----| |-----| |+---+| |+---+| |+---+|
||BD1|| ||BD1|| ||BD1|| ||BD1|| ||BD1|| ||BD1||
|+---+| |-----| |-----| |+---+| |+---+| |+---+|
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
PE2| PE3| PE4| PE2| PE3| PE4
- | - - - | - | - | - - - | -
| | | | | | | | |
v v v v v
| R1 R2 | R3 | R1 R2 | R3
- - - G1- - - - - - G1- - -
Figure 1 - Intra-subnet IP Multicast
Model (a) illustrated in Figure 1 is referred to as IP Multicast
delivery as BUM traffic. This way of delivering IP Multicast traffic
does not require any extensions to [RFC7432], however, it sends the
IP Multicast flows to non-interested receivers, such as e.g., R3 in
Figure 1. In this example, downstream PEs can snoop IGMP/MLD messages
from the receivers so that layer-2 multicast state is created and,
for instance, PE4 can avoid sending (S1,G1) to R3, since R3 is not
interested in (S1,G1).
Model (b) in Figure 1 uses an S-PMSI to optimize the delivery of the
(S1,G1) flow. For instance, assuming PE1 uses IR, PE1 sends (S1,G1)
only to the downstream PEs that issued an SMET route for (S1,G1),
that is, PE2 and PE3. In case PE1 uses any P-tunnel different than
IR, AR or BIER, PE1 will advertise an S-PMSI A-D route for (S1,G1)
and PE2/PE2 will join that tree.
Procedures for Model (b) are specified in [IGMP-PROXY].
1.2.2 Inter-subnet IP Multicast Forwarding
If the source and receivers are attached to different BDs of the same
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tenant domain, the EVPN network can also use Inclusive or Selective
Trees as depicted in Figure 2, models (a) and (b) respectively.
S1 + S1 +
(a) + | (b) + |
| | (S1,G1) | | (S1,G1)
PE1 | | PE1 | |
+-----+ v +-----+ v
|+---+| |+---+|
||BD1|| ||BD1||
|+---+| |+---+|
+-----+ +-----+
+-------|-------+ +-------|
| | | | |
v v v v v
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
|+---+| |+---+| |+---+| |+---+| |+---+| |+---+|
||SBD|| ||SBD|| ||SBD|| ||SBD|| ||SBD|| ||SBD||
|+-|-+| |+-|-+| |+---+| |+-|-+| |+-|-+| |+---+|
| VRF | | VRF | | VRF | | VRF | | VRF | | VRF |
|+-v-+| |+-v-+| |+---+| |+-v-+| |+-v-+| |+---+|
||BD2|| ||BD3|| ||BD4|| ||BD2|| ||BD3|| ||BD4||
|+-|-+| |+-|-+| |+---+| |+-|-+| |+-|-+| |+---+|
+--|--+ +--|--+ +-----+ +--|--+ +--|--+ +-----+
PE2| PE3| PE4 PE2| PE3| PE4
- | - - - | - - | - - - | -
| | | | | | | |
v v v v
| R1 R2 | R3 | R1 R2 | R3
- - - G1- - - - - - G1- - -
Figure 2 - Inter-subnet IP Multicast
[OISM] specifies the procedures to optimize the Inter-subnet
Multicast forwarding in an EVPN network. The IP Multicast flows are
always sent in the context of the source BD. As described in [OISM],
if the downstream PE is not attached to the source BD, the IP
Multicast flow is received on the SBD (Supplementary Broadcast
Domain), as in the example in Figure 2.
[OISM] supports Inclusive or Selective Multicast Trees, and as
explained in section 1.3.1 "Intra-subnet IP Multicast Forwarding",
the Selective Multicast Trees are setup in a different way, depending
on the P-tunnel being used by the source BD. As an example, model (a)
in Figure 2 illustrates the use of an Inclusive Multicast Tree for
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BD1 on PE1. Since the downstream PEs are not attached to BD1, they
will all receive (S1,G1) in the context of the SBD and will locally
route the flow to the local ACs. Model (b) uses a similar forwarding
model, however PE1 sends the (S1,G1) flow in a Selective Multicast
Tree. If the P-tunnel is IR, AR or BIER, PE1 does not need to
advertise an S-PMSI A-D route.
[OISM] is a superset of the procedures in [IGMP-PROXY], in which
sources and receivers can be in the same or different BD of the same
tenant. [OISM] ensures every upstream PE attached to a source will
learn of all other PEs (attached to the same Tenant Domain) that have
interest in a particular set of flows. This is because the downstream
PEs advertise SMET routes for a set of flows with the SBD's Route
Target and they are imported by all the Upstream PEs of the tenant.
As a result of that, inter-subnet multicasting can be done within the
Tenant Domain, without requiring any Rendezvous Points (RP), shared
trees, UMH selection or any other complex aspects of conventional
multicast routing techniques.
1.3 Multi-Homed IP Multicast Sources in EVPN
Contrary to conventional multicast routing technologies, multi-homing
PEs attached to the same source can never create IP Multicast packet
duplication if the PEs use a multi-homed Ethernet Segment (ES).
Figure 3 illustrates this by showing two multi-homing PEs (PE1 and
PE2) that are attached to the same source (S1). We assume that S1 is
connected to an all-active ES by a layer-2 switch (SW1) with a LAG to
PE1 and PE2.
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S1
|
v
+-----+
| SW1 |
+-----+
+---- | |
(S1,G1)| +----+ +----+
IGMP | | all-active |
J(S1,G1) PE1 v | ES-1 | PE2
+----> +-----------|---+ +---|-----------+
| +---+ +---+ | | +---+ |
R1 <-----|BD2| |BD1| | | |BD1| |
| +---+---+---+ | | +---+---+ |
+----| |VRF| | | | |VRF| |----+
| | +---+---+ | | | +---+---+ | |
| | |SBD| | | | |SBD| | |
| | +---+ | | | +---+ | |
| +------------|--+ +---------------+ |
| | |
| | |
| | |
| EVPN | ^ |
| OISM v PE3 | SMET |
| +---------------+ | (*,G1) |
| | +---+ | | |
| | |SBD| | |
| | +---+---+ | |
+--------------| |VRF| |----------------+
| +---+---+---+ |
| |BD2| |BD3| |
| +-|-+ +-|-+ |
+---|-------|---+
^ | | ^
IGMP | v v | IGMP
J(*,G1) | R2 R3 | J(S1,G1)
Figure 3 - All-active Multi-homing and OISM
When receiving the (S1,G1) flow from S1, SW1 will choose only one
link to send the flow, as per [RFC7432]. Assuming PE1 is the
receiving PE on BD1, the IP Multicast flow will be forwarded as soon
as BD1 creates multicast state for (S1,G1) or (*,G1). In the example
of Figure 3, receivers R1, R2 and R3 are interested in the multicast
flow to G1. R1 will receive (S1,G1) directly via the IRB interface as
per [OISM]. Upon receiving IGMP reports from R2 and R3, PE3 will
issue an SMET (*,G1) route that will create state in PE1's BD1. PE1
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will therefore forward the IP Multicast flow to PE3's SBD and PE3
will forward to R2 and R3, as per [OISM] procedures.
When IP Multicast source multi-homing is required, EVPN multi-homed
Ethernet Segments SHOULD be used. EVPN multi-homing guarantees that
only one Upstream PE will forward a given multicast flow at the time,
avoiding packet duplication at the Downstream PEs. In addition, the
SMET route for a given flow creates state in all the multi-homing
Upstream PEs. Therefore, in case of failure on the Upstream PE
forwarding the flow, the backup Upstream PE can forward the flow
immediately.
This document assumes that multi-homing PEs attached to the same
source always use multi-homed Ethernet Segments.
1.4 The Need for Redundant IP Multicast Sources in EVPN
While multi-homing PEs to the same IP Multicast G-source provides
certain level of resiliency, multicast applications are often
critical in the Operator's network and greater level of redundancy is
required. This document assumes that:
a) Redundant G-sources for an SFG may exist in the EVPN tenant
network. A Redundant G-source is a host or a router that sends an
SFG in a tenant network where there is another host or router
sending traffic to the same SFG.
b) Those redundant G-sources may be in the same BD or different BDs
of the tenant. There must not be restrictions imposed on the
location of the receiver systems either.
c) The redundant G-sources can be single-homed to only one EVPN PE or
multi-homed to multiple EVPN PEs.
d) The EVPN PEs must avoid duplication of the same SFG on the
receiver systems.
2. Solution Overview
There are two redundant G-source solutions described in this
document:
o Warm Standby (WS) Solution
o Hot Standby (HS) Solution
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The WS solution is an upstream PE based solution (downstream PEs do
not participate in the procedures), in which all the upstream PEs
attached to redundant G-sources for an SFG will elect a "Single
Forwarder" (SF) among themselves. Once a SF is elected, the upstream
PEs add an RPF check to the (*,G) state for the SFG:
- A non-SF upstream PE discards any (*,G) packets received over a
local AC.
- The SF accepts and forwards any (*,G) packets it receives over a
single local AC. In case (*,G) packets are received over multiple
local ACs, they will be discarded in all the local ACs but one. The
procedure to choose the local AC that accepts packets is a local
implementation matter.
A failure on the SF will result in the election of a new SF. The
Election requires BGP extensions on the existing EVPN routes. These
extensions and associated procedures are described in Sections 3 and
4 respectively.
In the HS solution the downstream PEs are the ones avoiding the SFG
duplication. The upstream PEs are aware of the locally attached G-
sources and add a unique ESI-label per SFG to the SFG packets
forwarded to downstream PEs. The downstream PEs pull the SFG from all
the upstream PEs attached to the redundant G-sources and avoid
duplication on the receiver systems by adding an RPF check to the
(*,G) state for the SFG:
- A downstream PE discards any (*,G) packets it receives from the
"wrong G-source".
- The wrong G-source is identified in the data path by an ESI-label
that is different than the ESI-label used for the selected G-
source.
- Note that the ESI-label is used here for "ingress filtering" as
opposed to the [RFC7432] "egress filtering" used in the split-
horizon procedures. In [RFC7432] the ESI-label indicates what
egress ACs must be skipped when forwarding BUM traffic to the
egress. In this document, the ESI-label indicates what ingress
traffic must be discarded.
The use of ESI-labels for SFGs forwarded by upstream PEs require some
control plane and data plane extensions in the procedures used by
[RFC7432] for multi-homing. Upon failure of the selected G-source,
the downstream PE will switch over to a different selected G-source,
and will therefore change the RPF check for the (*,G) state. The
extensions and associated procedures are described in Sections 3 and
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5 respectively.
An operator should use the HS solution if they require a fast fail-
over time and the additional bandwidth consumption is acceptable (SFG
packets are received multiple times on the downstream PEs). Otherwise
the operator should use the WS solution, at the expense of a slower
fail-over time in case of a G-source or upstream PE failure. Besides
bandwidth efficiency, another advantage of the WS solution is that
only the upstream PEs attached to the redundant G-sources for the
same SFG need to be upgraded to support the new procedures.
The support of either solution is OPTIONAL.
3. BGP EVPN Extensions
This document makes use of the following BGP EVPN extensions:
1. SFG flag in the Multicast Flags Extended Community
The Single Flow Group (SFG) flag is a new bit requested to IANA
out of the registry Multicast Flags Extended Community Flag
Values. This new flag is set for S-PMSI routes that carry an SFG
(*,G) in the NLRI.
2. ESI attribute
The HS solution requires the advertisement of one or more
attributes that encode the Ethernet Segment Identifier(s)
associated to an S-PMSI (*,G) route that advertises the presence
of an SFG. The format of this attribute will be described in
future revisions of this document. The following options are being
considered for the "ESI attribute":
- Use a BGP Large Community (LC) Attribute:
If an Ethernet Segment Type 5 [RFC7432] is used for ESes
attached to redundant G-sources, a LC attribute can be used
where each value encodes the corresponding ESI in the following
format: ASN(4-bytes):Local-Discriminator(4-bytes):0x0(4-bytes);
ASN and Local-Discriminator are the same values that are used at
the upstream PE to construct the type-5 ESI. A PE receiving an
S-PMSI (*,G) route with an SFG indication should interpret the
LC Attribute as a list of ESIs associated with the redundant G-
sources.
- Use a new BGP attribute
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Another option is to define a new attribute that can encode one
or more ESI values.
- Use an IPv6 Address Specific BGP Extended Community Attribute
Another Option is to make use of the [RFC5701] IPv6 Address EC
attribute.
This section will be modified in future versions of the document.
4. Warm Standby (WS) Solution for Redundant G-Sources
The general procedure is described as follows:
1. Configuration of the upstream PEs
Upstream PEs where redundant G-sources may exist need to be
configured to know which groups are carrying only flows from
redundant G-sources, that is, the SFGs in the tenant domain. They
will also be configured to know which local BDs may be attached to
a redundant G-source. As an example, PE1 is configured to know
that G1 is an SFG and redundant G-sources for G1 may be attached
to BD1 or BD2.
2. Signaling the location of a G-source for a given SFG
Upon receiving G-traffic for an SFG on a BD, an upstream PE
configured to follow this procedure, e.g., PE1:
a. Originates an S-PMSI (*,G) route for the SFG that is imported
by all the PEs attached to the tenant domain. In order to do
that, the route will use the SBD-RT (Supplementary Broadcast
Domain Route-Target) in addition to the BD-RT of the BD over
which the G-traffic is received. The route SHOULD also carry a
DF Election Extended Community (EC) and a flag indicating that
it conveys an SFG. The DF Election EC and its use is specified
in [DF].
b. The above S-PMSI route MAY be advertised with or without PMSI
Tunnel Attribute (PTA):
- With no PTA if an I-PMSI or S-PMSI with IR/AR/BIER are to be
used.
- With PTA in any other case.
c. The S-PMSI (*,G) route is triggered by the first packet of the
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SFG and withdrawn when the flow is not received anymore.
Detecting when the G-source is no longer active is a local
implementation matter. The use of a timer is RECOMMENDED. The
timer is started when the traffic to G1 is not received. Upon
expiration of the timer, the PE will withdraw the route.
3. Single Forwarder (SF) Election
If the PE with a local G-source receives an S-PMSI route for the
same SFG from a remote PE, it will run a Single Forwarder (SF)
Election based on the information encoded in the DF Election EC.
4. RPF check on the PEs attached to a redundant G-source
All the PEs with a local G-source for the SFG will add an RPF
check to the (*,G) state for the SFG. That RPF check depends on
the SF Election result:
a. The non-SF PEs discard any (*,G) packets received over a local
AC.
b. The SF accepts any (*,G) packets it receives over one (and only
one) local AC.
The solution above provides redundancy for SFGs and it does not
require an upgrade of the downstream PEs (PEs where there is
certainty that no redundant G-sources are connected). Other G-sources
for non-SFGs may exist in the same tenant domain. This document does
not change the existing procedures for non-SFG G-sources.
The redundant G-sources can be single-homed or multi-homed to a BD in
the tenant domain. Multi-homing does not change the above procedures.
Sections 4.1 and 4.2 show two examples of the WS solution.
4.1 WS Example in an OISM Network
Figure 4 illustrates an example in which S1 and S2 are redundant G-
sources for the SFG (*,G1).
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S1 (Single S2
| Forwarder) |
(S1,G1)| (S2,G1)|
| |
PE1 | PE2 |
+--------v---+ +--------v---+
S-PMSI | +---+ | | +---+ | S-PMSI
(*,G1) | +---|BD1| | | +---|BD2| | (*,G1)
Pref200 | |VRF+---+ | | |VRF+---+ | Pref100
|SFG |+---+ | | | |+---+ | | SFG|
| +----|SBD|--+ | |-----------||SBD|--+ |---+ |
v | |+---+ | | |+---+ | | v
| +---------|--+ +------------+ |
SMET | | | SMET
(*,G1) | | (S1,G1) | (*,G1)
| +--------+------------------+ |
^ | | | | ^
| | | EVPN | | |
| | | OISM | | |
| | | | | |
PE3 | | PE4 | | PE5
+--------v---+ +------------+ | +------------+
| +---+ | | +---+ | | | +---+ |
| +---|SBD| |-------| +---|SBD| |--|---| +---|SBD| |
| |VRF+---+ | | |VRF+---+ | | | |VRF+---+ |
|+---+ | | |+---+ | | | |+---+ | |
||BD3|--+ | ||BD4|--+ | +--->|BD1|--+ |
|+---+ | |+---+ | |+---+ |
+------------+ +------------+ +------------+
| ^ | ^
| | IGMP | | IGMP
R1 | J(*,G1) R3 | J(*,G1)
Figure 4 - WS Solution for Redundant G-Sources
The WS solution works as follows:
1. Configuration of the upstream PEs, PE1 and PE2
PE1 and PE2 are configured to know that G1 is an SFG and redundant
G-sources for G1 may be attached to BD1 or BD2, respectively.
2. Signaling the location of S1 and S2 for (*,G1)
Upon receiving (S1,G1) traffic on a local AC, PE1 and PE2
originate S-PMSI (*,G1) routes with the SBD-RT, DF Election
Extended Community (EC) and a flag indicating that it conveys an
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SFG.
3. Single Forwarder (SF) Election
Based on the DF Election EC content, PE1 and PE2 elect an SF for
(*,G1). Assuming both PEs agree on e.g., Preference based Election
as the algorithm to use [DF-PREF], and PE1 has a higher
preference, PE1 becomes the SF for (*,G1).
4. RPF check on the PEs attached to a redundant G-source
a. The non-SF, PE2, discards any (*,G1) packets received over a
local AC.
b. The SF, PE1 accepts (*,G1) packets it receives over a one (and
only one) local AC.
The end result is that, upon receiving reports for (*,G1) or (S,G1),
the downstream PEs (PE3 and PE5) will issue SMET routes and will pull
the multicast SFG from PE1, and PE1 only. A failure on S1, the AC
connected to S1 or PE1 itself will trigger the S-PMSI (*,G1)
withdrawal from PE1 and PE2 will be promoted to SF.
4.2 WS Example in a Single-BD Tenant Network
Figure 5 illustrates an example in which S1 and S2 are redundant G-
sources for the SFG (*,G1), however, now all the G-sources and
receivers are connected to the same BD1 and there is no SBD.
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S1 (Single S2
| Forwarder) |
(S1,G1)| (S2,G1)|
| |
PE1 | PE2 |
+--------v---+ +--------v---+
S-PMSI | +---+ | | +---+ | S-PMSI
(*,G1) | |BD1| | | |BD1| | (*,G1)
Pref200 | +---+ | | +---+ | Pref100
|SFG | | | | | SFG|
| +---| | |-----------| |---+ |
v | | | | | | | v
| +---------|--+ +------------+ |
SMET | | | SMET
(*,G1) | | (S1,G1) | (*,G1)
| +--------+------------------------+ |
^ | | | | ^
| | | EVPN | | |
| | | | | |
| | | | | |
PE3 | | PE4 | | PE5
+--------v---+ +------------+ +-|----------+
| +---+ | | +---+ | | | +---+ |
| |BD1| |-------| |BD1| |------| +--->|BD1| |
| +---+ | | +---+ | | +---+ |
| | | | | |
| | | | | |
| | | | | |
+------------+ +------------+ +------------+
| ^ | ^
| | IGMP | | IGMP
R1 | J(*,G1) R3 | J(*,G1)
Figure 5 - WS Solution for Redundant G-Sources in the same BD
The same procedure as in Section 4.1 is valid here, being this a sub-
case of the one in Section 4.1. Upon receiving traffic for the SFG
G1, PE1 and PE2 advertise the S-PMSI routes with BD1-RT only, since
there is no SBD.
5. Hot Standby (HS) Solution for Redundant G-Sources
If fast-failover time is desired upon the failure of a G-source or PE
attached to the G-source, and in spite of the extra bandwidth
consumption in the tenant network, the HS solution should be used.
The procedure is as follows:
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1. Configuration of the PEs
As in the WS case, the upstream PEs where redundant G-sources may
exist need to be configured to know which groups are carrying only
flows from redundant G-sources, that is, the SFGs in the tenant
domain. In addition (and this is not done in WS) the individual
redundant G-sources for an SFG need to be associated with an
Ethernet Segment (ES) on the upstream PEs:
- This is irrespective of the redundant G-source being multi-homed
or single-homed. Even for single-homed redundant G-sources the
HS procedure relies on the ESI labels for the RPF check on
downstream PEs. The term "S-ESI" is used in this document to
refer to an ESI associated to a redundant G-source.
- The S-ESI SHOULD be a Type 5 ESI [RFC7432] so that it can be
mapped to a value in a BGP LC attribute, as described in Section
3. The S-ESI MAY also be configured.
Contrary to the WS method (that is transparent to the downstream
PEs), the support for the HS procedure in all downstream PEs
connected to the receivers in the tenant network is REQUIRED. The
downstream PEs do not need to be configured to know the connected
SFGs or their ESIs, since they get that information from the
upstream PEs. The downstream PEs will locally select an ESI for a
given SFG, and will program an RPF check to the (*,G) state for
the SFG that will discard (*,G) packets from the rest of the ESIs.
The selection of the ESI for the SFG is based on local policy.
2. Signaling the location of a G-source for a given SFG and its
association to the local ESIs
Based on the configuration in step 1, an upstream PE configured to
follow the HS procedures:
a. Advertises an S-PMSI (*,G) route per each configured SFG. These
routes need to be imported by all the PEs of the tenant domain,
therefore they will carry the BD-RT and SBD-RT (if the SBD
exists). The route also carries the ESI attribute that conveys
all the S-ESIs associated to the SFG in the PE.
b. The S-PMSI route will convey a PTA if the same cases as in the
WS procedure.
c. The S-PMSI (*,G) route is triggered by the configuration of the
SFG and not by the reception of G-traffic.
3. Distribution of DCB (Domain-wide Common Block) ESI-labels and G-
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source ES routes
An upstream PE advertises the corresponding ES, A-D per-EVI and A-
D per-ES routes for the local S-ESIs.
a. ES routes are used for regular DF Election for the S-ES. This
document does not introduce any change in the procedures
related to the ES routes.
b. The A-D per-EVI and A-D per-ES routes MUST include the SBD-RT
since they have to be imported by all the PEs in the tenant
domain.
c. The A-D per-ES routes convey the S-ESI labels that the
downstream PEs use to add the RPF check for the (*,G)
associated to the SFGs. This RPF check requires that all the
packets for a given G-source are received with the same S-ESI
label value on the downstream PEs. For example, if two
redundant G-sources are multi-homed to PE1 and PE2 via S-ES-1
and S-ES-2, PE1 and PE2 MUST allocate the same ESI label "Lx"
for S-ES-1 and they MUST allocate the same ESI label "Ly" for
S-ES-2. In addition, Lx and Ly MUST be different. These ESI
labels are Domain-wide Common Block (DCB) labels and follow the
procedures in [DCB].
4. Processing of A-D routes and RPF check on the downstream PEs
Unless described otherwise, "A-D routes" in this section refers to
both types, A-D per-ES and A-D per-EVI routes. The A-D routes are
received and imported in all the PEs in the tenant domain. The
processing of the A-D routes on a given PE depends on its
configuration:
a. The PEs attached to the same BD of the BD-RT that is included
in the A-D routes will process the routes as in [RFC7432] and
[DF]. If the receiving PE is attached to the same ES as
indicated in the route, [RFC7432] split-horizon procedures will
be followed and the DF Election candidate list may be modified
as in [DF] if the ES supports the AC-DF capability.
b. The PEs that are not attached to the BD-RT but are attached to
the SBD of the received SBD-RT, will import the A-D routes and
use them for redundant G-source mass withdrawal, as explained
later.
c. Upon importing A-D per-ES routes corresponding to different S-
ESes, a PE MUST select a primary S-ES and add an RPF check to
the (*,G) state in the BD or SBD. This RPF check will discard
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all ingress packets to (*,G) that are not received with the
ESI-label of the primary S-ES. The selection of the primary S-
ES is a matter of local policy.
5. G-traffic forwarding for redundant G-sources and fault detection
Assuming there is (*,G) or (S,G) state for the SFG with OIF list
entries associated to remote EVPN PEs, upon receiving G-traffic on
a S-ES, the upstream PE will add a S-ESI label at the bottom of
the stack before forwarding the traffic to the remote EVPN PEs.
This label is allocated from a DCB as described in step 3. If P2MP
or BIER PMSIs are used, this is not adding any new data path
procedures on the upstream PEs (except that the ESI-label is
allocated from a DCB). However, if IR/AR are used, this document
extends the [RFC7432] procedures by pushing the S-ESI labels not
only on packets sent to the PEs that shared the ES but also to the
rest of the PEs in the tenant domain. This allows the downstream
PEs to receive all the multicast packets from the redundant G-
sources with a S-ESI label (irrespective of the PMSI type and the
local ESes), and discard any packet that conveys a S-ESI label
different from the primary S-ESI label (that is, the label
associated to the selected primary S-ES), as discussed in step 4.
If the last A-D per-EVI or the last A-D per-ES route for the
primary S-ES is withdrawn, the downstream PE will immediately
select a new primary S-ES and will change the RPF check. Note that
if the S-ES is re-used for multiple tenant domains by the upstream
PEs, the withdrawal of all the A-D per-ES routes for a S-ES
provides a mass withdrawal capability that makes a downstream PE
to change the RPF check in all the tenant domains using the same
S-ES.
The withdrawal of the last S-PMSI route for a given (*,G) SHOULD
make the downstream PE remove the S-ESI label based RPF check on
(*,G).
5.1 Use of BFD in the HS Solution
This section will be completed in a future version of this document.
5.2 HS Example in an OISM Network
Figure 6 illustrates the HS model in an OISM network. As in previous
examples, S1 and S2 are redundant G-sources for the SFG (*,G1) in
BD1. S1 and S2 are (all-active) multi-homed to upstream PEs, PE1 and
PE2. The receivers are attached to downstream PEs, PE3 and PE5, in
BD3 and BD1, respectively. S1 and S2 are assumed to be connected by a
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LAG to the multi-homing PEs, and the multicast traffic can use the
link to either upstream PE. The diagram illustrates how S1 sends the
G-traffic to PE1 and PE1 forwards to the remote interested downstream
PEs, whereas S2 sends to PE2 and PE2 forwards further. In this HS
model, the interested downstream PEs will get duplicate G-traffic
from the two G-sources for the same SFG. While the diagram shows that
the two flows are forwarded by different upstream PEs, the all-active
multi-homing procedures may cause that the two flows come from the
same upstream PE. Therefore, finding out the upstream PE for the flow
is not enough for the downstream PEs to program the required RPF
check to avoid duplicate packets on the receiver.
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S1(ESI-1) S2(ESI-2)
| |
| +----------------------+
(S1,G1)| | (S2,G1)|
+----------------------+ |
PE1 | | PE2 | |
+--------v---+ +--------v---+
| +---+ | | +---+ | S-PMSI
S-PMSI | +---|BD1| | | +---|BD1| | (*,G1)
(*,G1) | |VRF+---+ | | |VRF+---+ | SFG
SFG |+---+ | | | |+---+ | | | ESI1,2
ESI1,2 +---||SBD|--+ | |-----------||SBD|--+ | |---+ |
| | |+---+ | | EVPN |+---+ | | | v
v | +---------|--+ OISM +---------|--+ |
| | | |
| | (S1,G1) | |
SMET | +---------+------------------+ | | SMET
(*,G1) | | | | | (*,G1)
^ | | +----------------------------+---+ | ^
| | | | (S2,G1) | | | |
| | | | | | | |
PE3 | | | PE4 | | | PE5
+-------v-v--+ +------------+ | | +------------+
| +---+ | | +---+ | | | | +---+ |
| +---|SBD| +-------| +---|SBD| |--|-|-| +---|SBD| |
| |VRF+---+ | | |VRF+---+ | | | | |VRF+---+ |
|+---+ | | |+---+ | | | | |+---+ | |
||BD3|--+ | ||BD4|--+ | | +->|BD1|--+ |
|+---+ | |+---+ | +--->+---+ |
+------------+ +------------+ +------------+
| ^ | ^
| | IGMP | | IGMP
R1 | J(*,G1) R3 | J(*,G1)
Figure 6 - HS Solution for Multi-homed Redundant G-Sources in OISM
In this scenario, the HS solution works as follows:
1. Configuration of the upstream PEs, PE1 and PE2
PE1 and PE2 are configured to know that G1 is an SFG and the
redundant G-sources for G1 use S-ESIs ESI-1 and ESI-2
respectively. Both ESes are configured in both PEs and the ESI
value can be configured or auto-derived as an ES type 5. The ESI-
label values are allocated from a DCB [DCB] and are configured
either locally or by a centralized controller. We assume ESI-1 is
configured to use ESI-label-1 and ESI-2 to use ESI-label-2.
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The downstream PEs, PE3, PE4 and PE5 are configured to support HS
mode and select the G-source with e.g., lowest ESI value.
2. PE1 and PE2 advertise S-PMSI (*,G1) and ES/A-D routes
Based on the configuration of step 1, PE1 and PE2 advertise an S-
PMSI (*,G1) route each. The route from each of the two PEs will
include the ESI attribute with ESI-1 and ESI-2, as well as BD1-RT
plus SBD-RT and a flag that indicates that G1 is an SFG.
In addition, PE1 and PE2 advertise ES and A-D routes for ESI-1 and
ESI-2. The A-D per-ES and per-EVI routes will include the SBD-RT
so that they can be imported by the downstream PEs that are not
attached to BD1, e.g., PE3 and PE4. The A-D per-ES routes will
convey ESI-label-1 for ESI-1 (on both PEs) and ESI-label-2 for
ESI-2 (also on both PEs).
3. Processing of A-D routes and RPF check
PE1 and PE2 received each other's ES and A-D routes. Regular
[RFC7432] [DF] procedures will be followed for DF Election and
programming of the ESI-labels for egress split-horizon filtering.
PE3/PE4 import the A-D routes in the SBD. Since PE3 has created a
(*,G1) state based on local interest, PE3 will add an RPF check to
(*,G1) so that packets coming with ESI-label-2 are discarded
(lowest ESI value is assumed to give the primary S-ES).
4. G-traffic forwarding and fault detection
PE1 receives G-traffic (S1,G1) on ES-1 that is forwarded within
the context of BD1. Irrespective of the tunnel type, PE1 pushes
ESI-label-1 at the bottom of the stack and the traffic gets to PE3
and PE5 with the mentioned ESI-label (PE4 has no local interested
receivers). The G-traffic with ESI-label-1 passes the RPF check
and it is forwarded to R1. In the same way, PE2 sends (S2,G1) with
ESI-label-2, but this G-traffic does not pass the RPF check and
gets discarded at PE3/PE5.
If the link from S1 to PE1 fails, S1 will forward the (S1,G1)
traffic to PE2 instead. PE1 withdraws the ES and A-D routes for
ESI-1. Now both flows will be originated by PE2, however the RPF
checks don't change in PE3/PE5.
If subsequently, the link from S1 to PE2 fails, PE2 also withdraws
the ES and A-D routes for ESI-1. Since PE3 and PE5 have no longer
A-D routes for ESI-1, they immediately change the RPF check so
that packets with ESI-label-2 are now accepted.
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Figure 7 illustrates a scenario where S1 and S2 are single-homed to
PE1 and PE2 respectively. This scenario is a sub-case of the one in
Figure 6. Now ES-1 only exists in PE1, hence only PE1 advertises the
A-D routes for ESI-1. Similarly, ES-2 only exists in PE2 and PE2 is
the only PE advertising A-D routes for ESI-2. The same procedures as
in Figure 6 applies to this use-case.
S1(ESI-1) S2(ESI-2)
| |
(S1,G1)| (S2,G1)|
| |
PE1 | PE2 |
+--------v---+ +--------v---+
| +---+ | | +---+ | S-PMSI
S-PMSI | +---|BD1| | | +---|BD2| | (*,G1)
(*,G1) | |VRF+---+ | | |VRF+---+ | SFG
SFG |+---+ | | | |+---+ | | | ESI2
ESI1 +---||SBD|--+ | |-----------||SBD|--+ | |---+ |
| | |+---+ | | EVPN |+---+ | | | v
v | +---------|--+ OISM +---------|--+ |
| | | |
| | (S1,G1) | |
SMET | +---------+------------------+ | | SMET
(*,G1) | | | | | (*,G1)
^ | | +--------------------------------+----+ | ^
| | | | (S2,G1) | | | |
| | | | | | | |
PE3 | | | PE4 | | | PE5
+-------v-v--+ +------------+ | +------v-----+
| +---+ | | +---+ | | | +---+ |
| +---|SBD| |-------| +---|SBD| |--|---| +---|SBD| |
| |VRF+---+ | | |VRF+---+ | | | |VRF+---+ |
|+---+ | | |+---+ | | | |+---+ | |
||BD3|--+ | ||BD4|--+ | +--->|BD1|--+ |
|+---+ | |+---+ | |+---+ |
+------------+ +------------+ +------------+
| ^ | ^
| | IGMP | | IGMP
R1 | J(*,G1) R3 | J(*,G1)
Figure 7 - HS Solution for single-homed Redundant G-Sources in OISM
5.3 HS Example in a Single-BD Tenant Network
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Irrespective of the redundant G-sources being multi-homed or single-
homed, if the tenant network has only one BD, e.g., BD1, the
procedures of Section 5.2 still apply, only that routes do not
include any SBD-RT and all the procedures apply to BD1 only.
6. Security Considerations
The same Security Considerations described in [OISM] are valid for
this document.
7. IANA Considerations
IANA is requested to allocate a Bit in the Multicast Flags Extended
Community.
8. References
8.1. Normative References
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based Ethernet
VPN", RFC 7432, DOI 10.17487/RFC7432, February 2015,
<https://www.rfc-editor.org/info/rfc7432>.
[RFC6513] Rosen, E., Ed., and R. Aggarwal, Ed., "Multicast in
MPLS/BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February 2012,
<https://www.rfc-editor.org/info/rfc6513>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP VPNs", RFC
6514, DOI 10.17487/RFC6514, February 2012, <https://www.rfc-
editor.org/info/rfc6514>.
[IGMP-PROXY] Sajassi, A. et al, "IGMP and MLD Proxy for EVPN", June
2018, work-in-progress, draft-ietf-bess-evpn-igmp-mld-proxy-02.
[OISM] Rosen, E. et al, "EVPN Optimized Inter-Subnet Multicast
(OISM) Forwarding", June 2018, work-in-progress, draft-ietf-bess-
evpn-irb-mcast-01.
[DF] Rabadan, J., Mohanty, S., Sajassi, A., Drake, J., Nagaraj, K.,
and S. Sathappan, "Framework for EVPN Designated Forwarder Election
Extensibility", internet-draft draft-ietf-bess-evpn-df-election-
framework-05.txt, October 2018.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March
1997, <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>.
[DCB] Zhang, Z. et al, "MVPN/EVPN Tunnel Aggregation with Common
Labels", April 2018, work-in-progress, draft-zzhang-bess-mvpn-evpn-
aggregation-label-01.
8.2. Informative References
[EVPN-RT5] Rabadan, J., Henderickx, W., Drake, J., Lin, W., and A.
Sajassi, "IP Prefix Advertisement in EVPN", internet-draft ietf-bess-
evpn-prefix-advertisement-11.txt, May 2018.
[EVPN-BUM] Zhang, Z., Lin, W., Rabadan, J., and K. Patel, "Updates
on EVPN BUM Procedures", internet-draft ietf-bess-evpn-bum-procedure-
updates-03, April 2018.
[DF-PREF] Rabadan, J., Sathappan, S., Przygienda, T., Lin, W.,
Drake, J., Sajassi, A., and S. Mohanty, "Preference-based EVPN DF
Election", internet-draft ietf-bess-evpn-pref-df-02.txt, October
2018.
[RFC5701] Rekhter, Y., "IPv6 Address Specific BGP Extended Community
Attribute", RFC 5701, DOI 10.17487/RFC5701, November 2009,
<https://www.rfc-editor.org/info/rfc5701>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006,
<https://www.rfc-editor.org/info/rfc4364>.
9. Acknowledgments
10. Contributors
Authors' Addresses
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Jorge Rabadan
Nokia
777 E. Middlefield Road
Mountain View, CA 94043 USA
Email: jorge.rabadan@nokia.com
Senthil Sathappan
Nokia
701 E. Middlefield Road
Mountain View, CA 94043 USA
Email: senthil.sathappan@nokia.com
Jayant Kotalwar
Nokia
701 E. Middlefield Road
Mountain View, CA 94043 USA
Email: jayant.kotalwar@nokia.com
Eric C. Rosen
Juniper Networks, Inc.
EMail: erosen@juniper.net
Zhaohui Zhang
Juniper Networks
EMail: zzhang@juniper.net
Wen Lin
Juniper Networks, Inc.
EMail: wlin@juniper.net
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