Optimized Ingress Replication solution for EVPN
draft-ietf-bess-evpn-optimized-ir-09
BESS Workgroup J. Rabadan, Ed.
Internet-Draft S. Sathappan
Intended status: Standards Track Nokia
Expires: March 27, 2022 W. Lin
Juniper Networks
M. Katiyar
Versa Networks
A. Sajassi
Cisco Systems
September 23, 2021
Optimized Ingress Replication solution for EVPN
draft-ietf-bess-evpn-optimized-ir-09
Abstract
Network Virtualization Overlay (NVO) networks using EVPN as control
plane may use Ingress Replication (IR) or PIM (Protocol Independent
Multicast) based trees to convey the overlay Broadcast, Unknown
unicast and Multicast (BUM) traffic. PIM provides an efficient
solution to avoid sending multiple copies of the same packet over the
same physical link, however it may not always be deployed in the NVO
core network. IR avoids the dependency on PIM in the NVO network
core. While IR provides a simple multicast transport, some NVO
networks with demanding multicast applications require a more
efficient solution without PIM in the core. This document describes
a solution to optimize the efficiency of IR in NVO networks.
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). Note that other groups may also distribute
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Drafts is at https://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on March 27, 2022.
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Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology and Conventions . . . . . . . . . . . . . . . . . 4
3. Solution requirements . . . . . . . . . . . . . . . . . . . . 6
4. EVPN BGP Attributes for optimized-IR . . . . . . . . . . . . 6
5. Non-selective Assisted-Replication (AR) Solution Description 10
5.1. Non-selective AR-REPLICATOR procedures . . . . . . . . . 11
5.2. Non-selective AR-LEAF procedures . . . . . . . . . . . . 12
5.3. RNVE procedures . . . . . . . . . . . . . . . . . . . . . 15
6. Selective Assisted-Replication (AR) Solution Description . . 15
6.1. Selective AR-REPLICATOR procedures . . . . . . . . . . . 15
6.2. Selective AR-LEAF procedures . . . . . . . . . . . . . . 18
7. Pruned-Flood-Lists (PFL) . . . . . . . . . . . . . . . . . . 20
7.1. A PFL example . . . . . . . . . . . . . . . . . . . . . . 20
8. AR Procedures for single-IP AR-REPLICATORS . . . . . . . . . 21
9. AR Procedures and EVPN All-Active Multi-homing Split-Horizon 22
9.1. Ethernet Segments on AR-LEAF nodes . . . . . . . . . . . 22
9.2. Ethernet Segments on AR-REPLICATOR nodes . . . . . . . . 22
10. Security Considerations . . . . . . . . . . . . . . . . . . . 23
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 24
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
14.1. Normative References . . . . . . . . . . . . . . . . . . 25
14.2. Informative References . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
Ethernet Virtual Private Networks (EVPN) may be used as the control
plane for a Network Virtualization Overlay (NVO) network. Network
Virtualization Edge (NVE) devices and Provider Edges (PEs) that are
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part of the same EVPN Instance (EVI) use Ingress Replication (IR) or
PIM-based trees to transport the tenant's Broadcast, Unknown unicast
and Multicast (BUM) traffic. In NVO networks where PIM-based trees
cannot be used, IR is the only option. Examples of these situations
are NVO networks where the core nodes don't support PIM or the
network operator does not want to run PIM in the core.
In some use-cases, the amount of replication for BUM traffic is kept
under control on the NVEs due to the following fairly common
assumptions:
a. Broadcast is greatly reduced due to the proxy ARP (Address
Resolution Protocol) and proxy ND (Neighbor Discovery)
capabilities supported by EVPN on the NVEs. Some NVEs can even
provide Dynamic Host Configuration Protocol (DHCP) server
functions for the attached Tenant Systems (TS) reducing the
broadcast even further.
b. Unknown unicast traffic is greatly reduced in virtualized NVO
networks where all the MAC and IP addresses are learned in the
control plane.
c. Multicast applications are not used.
If the above assumptions are true for a given NVO network, then IR
provides a simple solution for multi-destination traffic. However,
the statement c) above is not always true and multicast applications
are required in many use-cases.
When the multicast sources are attached to NVEs residing in
hypervisors or low-performance-replication TORs (Top Of Rack
switches), the ingress replication of a large amount of multicast
traffic to a significant number of remote NVEs/PEs can seriously
degrade the performance of the NVE and impact the application.
This document describes a solution that makes use of two IR
optimizations:
1. Assisted-Replication (AR)
2. Pruned-Flood-Lists (PFL)
Both optimizations may be used together or independently so that the
performance and efficiency of the network to transport multicast can
be improved. Both solutions require some extensions to [RFC7432]
that are described in Section 4.
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Section 3 lists the requirements of the combined optimized-IR
solution, whereas Section 5 and Section 6 describe the Assisted-
Replication (AR) solution, and Section 7 the Pruned-Flood-Lists (PFL)
solution.
2. Terminology and Conventions
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.
The following terminology is used throughout the document:
- AC: Attachment Circuit
- BM traffic: Refers to Broadcast and Multicast frames (excluding
unknown unicast frames)
- NVO: Network Virtualization Overlay
- NVE: Network Virtualization Edge router
- PE: Provider Edge router
- AR-REPLICATOR: Assisted Replication - REPLICATOR, refers to an
NVE/PE that can replicate Broadcast or Multicast traffic received
on overlay tunnels to other overlay tunnels. This document
defines the control and data plane procedures that an AR-
REPLICATOR needs to follow.
- AR-LEAF: Assisted Replication - LEAF, refers to an NVE/PE that -
given its poor replication performance - sends all the Broadcast
and Multicast traffic to an AR-REPLICATOR that can replicate the
traffic further on its behalf.
- RNVE: Regular NVE, refers to an NVE that supports the procedures
of [RFC8365] and does not support the procedures in this document.
However, this document defines procedures to interoperate with
RNVEs.
- Replicator-AR route: an EVPN RT-3 (route type 3) that is
advertised by an AR-REPLICATOR to signal its capabilities.
- Regular-IR: Refers to Regular Ingress Replication, where the
source NVE/PE sends a copy to each remote NVE/PE part of the BD.
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- AR-IP: IP address owned by the AR-REPLICATOR and used to
differentiate the ingress traffic that must follow the AR
procedures.
- IR-IP: IP address used for Ingress Replication as in [RFC7432].
- AR-VNI: VNI advertised by the AR-REPLICATOR along with the
Replicator-AR route. It is used to identify the ingress packets
that must follow AR procedures ONLY in the Single-IP AR-REPLICATOR
case.
- IR-VNI: VNI advertised along with the RT-3 for IR.
- AR forwarding mode: for an AR-LEAF, it means sending an AC BM
packet to a single AR-REPLICATOR with tunnel destination IP AR-IP.
For an AR-REPLICATOR, it means sending a BM packet to a selected
number or all the overlay tunnels when the packet was previously
received from an overlay tunnel.
- IR forwarding mode: it refers to the Ingress Replication behavior
explained in [RFC7432]. It means sending an AC BM packet copy to
each remote PE/NVE in the BD and sending an overlay BM packet only
to the ACs and not other overlay tunnels.
- PTA: PMSI Tunnel Attribute
- RT-3: EVPN Route Type 3, Inclusive Multicast Ethernet Tag route
- RT-11: EVPN Route Type 11, Leaf Auto-Discovery (A-D) route
- VXLAN: Virtual Extensible LAN
- GRE: Generic Routing Encapsulation
- NVGRE: Network Virtualization using Generic Routing Encapsulation
- GENEVE: Generic Network Virtualization Encapsulation
- VNI: VXLAN Network Identifier
- EVI: EVPN Instance. An EVPN instance spanning the Provider Edge
(PE) devices participating in that EVPN
- BD: Broadcast Domain, as defined in [RFC7432].
- TOR: Top Of Rack switch
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3. Solution requirements
The IR optimization solution specified in this document (optimized-IR
hereafter) meets the following requirements:
a. It provides an IR optimization for BM (Broadcast and Multicast)
traffic without the need for PIM, while preserving the packet
order for unicast applications, i.e., known and unknown unicast
traffic should follow the same path. This optimization is
required in low-performance NVEs.
b. It reduces the flooded traffic in NVO networks where some NVEs do
not need broadcast/multicast and/or unknown unicast traffic.
c. The solution is compatible with [RFC7432] and [RFC8365] and has
no impact on the EVPN procedures for BM traffic. In particular,
the solution supports the following EVPN functions:
o All-active multi-homing, including the split-horizon and
Designated Forwarder (DF) functions.
o Single-active multi-homing, including the DF function.
o Handling of multi-destination traffic and processing of
broadcast and multicast as per [RFC7432].
d. The solution is backwards compatible with existing NVEs using a
non-optimized version of IR. A given BD can have NVEs/PEs
supporting regular-IR and optimized-IR.
e. The solution is independent of the NVO specific data plane
encapsulation and the virtual identifiers being used, e.g.: VXLAN
VNIs, NVGRE VSIDs or MPLS labels, as long as the tunnel is IP-
based.
4. EVPN BGP Attributes for optimized-IR
This solution extends the [RFC7432] Inclusive Multicast Ethernet Tag
routes and attributes so that an NVE/PE can signal its optimized-IR
capabilities.
The Inclusive Multicast Ethernet Tag route (RT-3) and its PMSI Tunnel
Attribute's (PTA) general format used in [RFC7432] are shown below:
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+---------------------------------+
| RD (8 octets) |
+---------------------------------+
| Ethernet Tag ID (4 octets) |
+---------------------------------+
| IP Address Length (1 octet) |
+---------------------------------+
| Originating Router's IP Addr |
| (4 or 16 octets) |
+---------------------------------+
+---------------------------------+
| Flags (1 octet) |
+---------------------------------+
| Tunnel Type (1 octets) |
+---------------------------------+
| MPLS Label (3 octets) |
+---------------------------------+
| Tunnel Identifier (variable) |
+---------------------------------+
The Flags field is 8 bits long. This document defines the use of 4
bits of this Flags field:
- bits 3 and 4, forming together the Assisted-Replication Type (T)
field
- bit 5, called the Broadcast and Multicast (BM) flag
- bit 6, called the Unknown (U) flag
Bits 5 and 6 are collectively referred to as the PFL (Pruned-Flood
Lists) flags.
The T field and PFL flags are defined as follows:
- T is the AR Type field (2 bits) that defines the AR role of the
advertising router:
o 00 (decimal 0) = RNVE (non-AR support)
o 01 (decimal 1) = AR-REPLICATOR
o 10 (decimal 2) = AR-LEAF
o 11 (decimal 3) = RESERVED
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- The PFL (Pruned-Flood-Lists) flags define the desired behavior of
the advertising router for the different types of traffic:
o Broadcast and Multicast (BM) flag. BM=1 means "prune-me" from
the BM flooding list. BM=0 means regular behavior.
o Unknown (U) flag. U=1 means "prune-me" from the Unknown
flooding list. U=0 means regular behavior.
- Flag L is an existing flag defined in [RFC6514] (L=Leaf
Information Required) and it will be used only in the Selective AR
Solution.
Please refer to Section 11 for the IANA considerations related to the
PTA flags.
In this document, the above RT-3 and PTA can be used in two different
modes for the same BD:
- Regular-IR route: in this route, Originating Router's IP Address,
Tunnel Type (0x06), MPLS Label and Tunnel Identifier MUST be used
as described in [RFC7432] when Ingress Replication is in use. The
NVE/PE that advertises the route will set the Next-Hop to an IP
address that we denominate IR-IP in this document. When
advertised by an AR-LEAF node, the Regular-IR route SHOULD be
advertised with type T= AR-LEAF.
- Replicator-AR route: this route is used by the AR-REPLICATOR to
advertise its AR capabilities, with the fields set as follows:
o Originating Router's IP Address MUST be set to an IP address of
the PE that should be common to all the EVIs on the PE (usually
this is the PE's loopback address). The Tunnel Identifier and
Next-Hop SHOULD be set to the same IP address as the
Originating Router's IP address when the NVE/PE originates the
route. The Next-Hop address is referred to as the AR-IP and
SHOULD be different than the IR-IP for a given PE/NVE.
o Tunnel Type = Assisted-Replication Tunnel. Section 11 provides
the allocated type value.
o T (AR role type) = 01 (AR-REPLICATOR).
o L (Leaf Information Required) = 0 (for non-selective AR) or 1
(for selective AR).
In addition, this document also uses the Leaf A-D route (RT-11)
defined in [I-D.ietf-bess-evpn-bum-procedure-updates] in case the
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selective AR mode is used. The Leaf A-D route MAY be used by the AR-
LEAF in response to a Replicator-AR route (with the L flag set) to
advertise its desire to receive the BM traffic from a specific AR-
REPLICATOR. It is only used for selective AR and its fields are set
as follows:
o Originating Router's IP Address is set to the advertising PE's
IP address (same IP used by the AR-LEAF in regular-IR routes).
The Next-Hop address is set to the IR-IP.
o Route Key is the "Route Type Specific" NLRI of the Replicator-
AR route for which this Leaf A-D route is generated.
o The AR-LEAF constructs an IP-address-specific route-target as
indicated in [I-D.ietf-bess-evpn-bum-procedure-updates], by
placing the IP address carried in the Next-Hop field of the
received Replicator-AR route in the Global Administrator field
of the Community, with the Local Administrator field of this
Community set to 0. Note that the same IP-address-specific
import route-target is auto-configured by the AR-REPLICATOR
that sent the Replicator-AR, in order to control the acceptance
of the Leaf A-D routes.
o The Leaf A-D route MUST include the PMSI Tunnel attribute with
the Tunnel Type set to AR, type set to AR-LEAF and the Tunnel
Identifier set to the IP of the advertising AR-LEAF. The PMSI
Tunnel attribute MUST carry a downstream-assigned MPLS label or
VNI that is used by the AR-REPLICATOR to send traffic to the
AR-LEAF.
Each AR-enabled node MUST understand and process the AR type field in
the PTA (Flags field) of the routes, and MUST signal the
corresponding type (1 or 2) according to its administrative choice.
Each node attached to the BD may understand and process the BM/U
flags. Note that these BM/U flags may be used to optimize the
delivery of multi-destination traffic and its use SHOULD be an
administrative choice, and independent of the AR role.
Non-optimized-IR nodes will be unaware of the new PMSI attribute flag
definition as well as the new Tunnel Type (AR), i.e. they will ignore
the information contained in the flags field for any RT-3 and will
ignore the RT-3 routes with an unknown Tunnel Type (type AR in this
case).
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5. Non-selective Assisted-Replication (AR) Solution Description
Figure 1 illustrates an example NVO network where the non-selective
AR function is enabled. Three different roles are defined for a
given BD: AR-REPLICATOR, AR-LEAF and RNVE (Regular NVE). The
solution is called "non-selective" because the chosen AR-REPLICATOR
for a given flow MUST replicate the BM traffic to 'all' the NVE/PEs
in the BD except for the source NVE/PE.
( )
(_ WAN _)
+---(_ _)----+
| (_ _) |
PE1 | PE2 |
+------+----+ +----+------+
TS1--+ (BD-1) | | (BD-1) +--TS2
|REPLICATOR | |REPLICATOR |
+--------+--+ +--+--------+
| |
+--+----------------+--+
| |
| |
+----+ VXLAN/nvGRE/MPLSoGRE +----+
| | IP Fabric | |
| | | |
NVE1 | +-----------+----------+ | NVE3
Hypervisor| TOR | NVE2 |Hypervisor
+---------+-+ +-----+-----+ +-+---------+
| (BD-1) | | (BD-1) | | (BD-1) |
| LEAF | | RNVE | | LEAF |
+--+-----+--+ +--+-----+--+ +--+-----+--+
| | | | | |
VM11 VM12 TS3 TS4 VM31 VM32
Figure 1: Optimized-IR scenario
In AR BDs such as BD-1 in the example, BM (Broadcast and Multicast)
traffic between two NVEs may follow a different path than unicast
traffic. This solution recommends the replication of BM through the
AR-REPLICATOR node, whereas unknown/known unicast will be delivered
directly from the source node to the destination node without being
replicated by any intermediate node. Unknown unicast SHALL follow
the same path as known unicast traffic in order to avoid packet
reordering for unicast applications and simplify the control and data
plane procedures.
Note that known unicast forwarding is not impacted by this solution.
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5.1. Non-selective AR-REPLICATOR procedures
An AR-REPLICATOR is defined as an NVE/PE capable of replicating
ingress BM (Broadcast and Multicast) traffic received on an overlay
tunnel to other overlay tunnels and local Attachment Circuits (ACs).
The AR-REPLICATOR signals its role in the control plane and
understands where the other roles (AR-LEAF nodes, RNVEs and other AR-
REPLICATORs) are located. A given AR-enabled BD service may have
zero, one or more AR-REPLICATORs. In our example in Figure 1, PE1
and PE2 are defined as AR-REPLICATORs. The following considerations
apply to the AR-REPLICATOR role:
a. The AR-REPLICATOR role SHOULD be an administrative choice in any
NVE/PE that is part of an AR-enabled BD. This administrative
option to enable AR-REPLICATOR capabilities MAY be implemented as
a system level option as opposed to as a per-BD option.
b. An AR-REPLICATOR MUST advertise a Replicator-AR route and MAY
advertise a Regular-IR route. The AR-REPLICATOR MUST NOT
generate a Regular-IR route if it does not have local attachment
circuits (AC). If the Regular-IR route is advertised, the AR
Type field is set to zero.
c. The Replicator-AR and Regular-IR routes are generated according
to section 3. The AR-IP and IR-IP used by the AR-REPLICATOR are
different routable IP addresses.
d. When a node defined as AR-REPLICATOR receives a BM packet on an
overlay tunnel, it will do a tunnel destination IP lookup and
apply the following procedures:
o If the destination IP is the AR-REPLICATOR IR-IP Address the
node will process the packet normally as in [RFC7432].
o If the destination IP is the AR-REPLICATOR AR-IP Address the
node MUST replicate the packet to local ACs and overlay
tunnels (excluding the overlay tunnel to the source of the
packet). When replicating to remote AR-REPLICATORs the tunnel
destination IP will be an IR-IP. That will be an indication
for the remote AR-REPLICATOR that it MUST NOT replicate to
overlay tunnels. The tunnel source IP used by the AR-
REPLICATOR MUST be its IR-IP when replicating to either AR-
REPLICATOR or AR-LEAF nodes.
An AR-REPLICATOR will follow a data path implementation compatible
with the following rules:
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- The AR-REPLICATORs will build a flooding list composed of ACs and
overlay tunnels to remote nodes in the BD. Some of those overlay
tunnels MAY be flagged as non-BM receivers based on the BM flag
received from the remote nodes in the BD.
- When an AR-REPLICATOR receives a BM packet on an AC, it will
forward the BM packet to its flooding list (including local ACs
and remote NVE/PEs), skipping the non-BM overlay tunnels.
- When an AR-REPLICATOR receives a BM packet on an overlay tunnel,
it will check the destination IP of the underlay IP header and:
o If the destination IP matches its AR-IP, the AR-REPLICATOR will
forward the BM packet to its flooding list (ACs and overlay
tunnels) excluding the non-BM overlay tunnels. The AR-
REPLICATOR will do source squelching to ensure the traffic is
not sent back to the originating AR-LEAF.
o If the destination IP matches its IR-IP, the AR-REPLICATOR will
skip all the overlay tunnels from the flooding list, i.e. it
will only replicate to local ACs. This is the regular IR
behavior described in [RFC7432].
- While the forwarding behavior in AR-REPLICATORs and AR-LEAF nodes
is different for BM traffic, as far as Unknown unicast traffic
forwarding is concerned, AR-LEAF nodes behave exactly in the same
way as AR-REPLICATORs do.
- The AR-REPLICATOR/LEAF nodes will build an Unknown unicast flood-
list composed of ACs and overlay tunnels to the IR-IP Addresses of
the remote nodes in the BD. Some of those overlay tunnels MAY be
flagged as non-U (Unknown unicast) receivers based on the U flag
received from the remote nodes in the BD.
o When an AR-REPLICATOR/LEAF receives an unknown packet on an AC,
it will forward the unknown packet to its flood-list, skipping
the non-U overlay tunnels.
o When an AR-REPLICATOR/LEAF receives an unknown packet on an
overlay tunnel will forward the unknown packet to its local ACs
and never to an overlay tunnel. This is the regular IR
behavior described in [RFC7432].
5.2. Non-selective AR-LEAF procedures
AR-LEAF is defined as an NVE/PE that - given its poor replication
performance - sends all the BM traffic to an AR-REPLICATOR that can
replicate the traffic further on its behalf. It MAY signal its AR-
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LEAF capability in the control plane and understands where the other
roles are located (AR-REPLICATOR and RNVEs). A given service can
have zero, one or more AR-LEAF nodes. Figure 1 shows NVE1 and NVE3
(both residing in hypervisors) acting as AR-LEAF. The following
considerations apply to the AR-LEAF role:
a. The AR-LEAF role SHOULD be an administrative choice in any NVE/PE
that is part of an AR-enabled BD. This administrative option to
enable AR-LEAF capabilities MAY be implemented as a system level
option as opposed to as per-BD option.
b. In this non-selective AR solution, the AR-LEAF MUST advertise a
single Regular-IR inclusive multicast route as in [RFC7432]. The
AR-LEAF SHOULD set the AR Type field to AR-LEAF. Note that
although this flag does not make any difference for the egress
nodes when creating an EVPN destination to the AR-LEAF, it is
RECOMMENDED to use this flag for an easy operation and
troubleshooting of the BD.
c. In a service where there are no AR-REPLICATORs, the AR-LEAF MUST
use regular ingress replication. This will happen when a new
update from the last former AR-REPLICATOR is received and
contains a non-REPLICATOR AR type, or when the AR-LEAF detects
that the last AR-REPLICATOR is down (via next-hop tracking in the
IGP or any other detection mechanism). Ingress replication MUST
use the forwarding information given by the remote Regular-IR
Inclusive Multicast Routes as described in [RFC7432].
d. In a service where there is one or more AR-REPLICATORs (based on
the received Replicator-AR routes for the BD), the AR-LEAF can
locally select which AR-REPLICATOR it sends the BM traffic to:
o A single AR-REPLICATOR MAY be selected for all the BM packets
received on the AR-LEAF attachment circuits (ACs) for a given
BD. This selection is a local decision and it does not have
to match other AR-LEAF's selection within the same BD.
o An AR-LEAF MAY select more than one AR-REPLICATOR and do
either per-flow or per-BD load balancing.
o In case of a failure on the selected AR-REPLICATOR, another
AR-REPLICATOR will be selected.
o When an AR-REPLICATOR is selected, the AR-LEAF MUST send all
the BM packets to that AR-REPLICATOR using the forwarding
information given by the Replicator-AR route for the chosen
AR-REPLICATOR, with tunnel type = 0x0A (AR tunnel). The
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underlay destination IP address MUST be the AR-IP advertised
by the AR-REPLICATOR in the Replicator-AR route.
o AR-LEAF nodes SHALL send service-level BM control plane
packets following regular IR procedures. An example would be
IGMP, MLD or PIM multicast packets. The AR-REPLICATORs MUST
NOT replicate these control plane packets to other overlay
tunnels since they will use the regular IR-IP Address.
e. The use of an AR-REPLICATOR-activation-timer (in seconds, default
value is 3) on the AR-LEAF nodes is RECOMMENDED. Upon receiving
a new Replicator-AR route where the AR-REPLICATOR is selected,
the AR-LEAF will run a timer before programming the new AR-
REPLICATOR. In case of a new added AR-REPLICATOR, or in case the
AR-REPLICATOR reboots, this timer will give the AR-REPLICATOR
some time to program the AR-LEAF nodes before the AR-LEAF sends
BM traffic. The AR-REPLICATOR-activation-timer SHOULD be
configurable in seconds, and its value account for the time it
takes for the AR-LEAF Regular-IR inclusive multicast route to get
to the AR-REPLICATOR and be programmed. While the AR-REPLICATOR-
activation-time is running, the AR-LEAF node will use regular
ingress replication.
An AR-LEAF will follow a data path implementation compatible with the
following rules:
- The AR-LEAF nodes will build two flood-lists:
1. Flood-list #1 - composed of ACs and an AR-REPLICATOR-set of
overlay tunnels. The AR-REPLICATOR-set is defined as one or
more overlay tunnels to the AR-IP Addresses of the remote AR-
REPLICATOR(s) in the BD. The selection of more than one AR-
REPLICATOR is described in point d) above and it is a local
AR-LEAF decision.
2. Flood-list #2 - composed of ACs and overlay tunnels to the
remote IR-IP Addresses.
- When an AR-LEAF receives a BM packet on an AC, it will check the
AR-REPLICATOR-set:
o If the AR-REPLICATOR-set is empty, the AR-LEAF will send the
packet to flood-list #2.
o If the AR-REPLICATOR-set is NOT empty, the AR-LEAF will send
the packet to flood-list #1, where only one of the overlay
tunnels of the AR-REPLICATOR-set is used.
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- When an AR-LEAF receives a BM packet on an overlay tunnel, will
forward the BM packet to its local ACs and never to an overlay
tunnel. This is the regular IR behavior described in [RFC7432].
- AR-LEAF nodes process Unknown unicast traffic in the same way AR-
REPLICATORS do, as described in section Section 5.1.
5.3. RNVE procedures
RNVE (Regular Network Virtualization Edge node) is defined as an NVE/
PE without AR-REPLICATOR or AR-LEAF capabilities that does IR as
described in [RFC7432]. The RNVE does not signal any AR role and is
unaware of the AR-REPLICATOR/LEAF roles in the BD. The RNVE will
ignore the Flags in the Regular-IR routes and will ignore the
Replicator-AR routes (due to an unknown tunnel type in the PTA) and
the Leaf A-D routes (due to the IP-address-specific route-target).
This role provides EVPN with the backwards compatibility required in
optimized-IR BDs. Figure 1 shows NVE2 as RNVE.
6. Selective Assisted-Replication (AR) Solution Description
Figure 1 is also used to describe the selective AR solution, however
in this section we consider NVE2 as one more AR-LEAF for BD-1. The
solution is called "selective" because a given AR-REPLICATOR MUST
replicate the BM traffic to only the AR-LEAF that requested the
replication (as opposed to all the AR-LEAF nodes) and MAY replicate
the BM traffic to the RNVEs. The same AR roles defined in Section 4
are used here, however the procedures are different.
The following sub-sections describe the differences in the procedures
of AR-REPLICATOR/LEAFs compared to the non-selective AR solution.
There is no change on the RNVEs.
6.1. Selective AR-REPLICATOR procedures
In our example in Figure 1, PE1 and PE2 are defined as Selective AR-
REPLICATORs. The following considerations apply to the Selective AR-
REPLICATOR role:
a. The Selective AR-REPLICATOR capability SHOULD be an
administrative choice in any NVE/PE that is part of an AR-enabled
BD, as the AR role itself. This administrative option MAY be
implemented as a system level option as opposed to as a per-BD
option.
b. Each AR-REPLICATOR will build a list of AR-REPLICATOR, AR-LEAF
and RNVE nodes. In spite of the 'Selective' administrative
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option, an AR-REPLICATOR MUST NOT behave as a Selective AR-
REPLICATOR if at least one of the AR-REPLICATORs has the L flag
NOT set. If at least one AR-REPLICATOR sends a Replicator-AR
route with L=0 (in the BD context), the rest of the AR-
REPLICATORs will fall back to non-selective AR mode.
c. The Selective AR-REPLICATOR MUST follow the procedures described
in section Section 5.1, except for the following differences:
o The Replicator-AR route MUST include L=1 (Leaf Information
Required) in the Replicator-AR route. This flag is used by
the AR-REPLICATORs to advertise their 'selective' AR-
REPLICATOR capabilities. In addition, the AR-REPLICATOR auto-
configures its IP-address-specific import route-target as
described in section Section 4.
o The AR-REPLICATOR will build a 'selective' AR-LEAF-set with
the list of nodes that requested replication to its own AR-IP.
For instance, assuming NVE1 and NVE2 advertise a Leaf A-D
route with PE1's IP-address-specific route-target and NVE3
advertises a Leaf A-D route with PE2's IP-address-specific
route-target, PE1 MUST only add NVE1/NVE2 to its selective AR-
LEAF-set for BD-1, and exclude NVE3.
o When a node defined and operating as Selective AR-REPLICATOR
receives a packet on an overlay tunnel, it will do a tunnel
destination IP lookup and if the destination IP is the AR-
REPLICATOR AR-IP Address, the node MUST replicate the packet
to:
+ local ACs
+ overlay tunnels in the Selective AR-LEAF-set (excluding the
overlay tunnel to the source AR-LEAF).
+ overlay tunnels to the RNVEs if the tunnel source IP is the
IR-IP of an AR-LEAF (in any other case, the AR-REPLICATOR
MUST NOT replicate the BM traffic to remote RNVEs). In
other words, only the first-hop selective AR-REPLICATOR
will replicate to all the RNVEs.
+ overlay tunnels to the remote Selective AR-REPLICATORs if
the tunnel source IP is an IR-IP of its own AR-LEAF-set (in
any other case, the AR-REPLICATOR MUST NOT replicate the BM
traffic to remote AR-REPLICATORs), where the tunnel
destination IP is the AR-IP of the remote Selective AR-
REPLICATOR. The tunnel destination IP AR-IP will be an
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indication for the remote Selective AR-REPLICATOR that the
packet needs further replication to its AR-LEAFs.
A Selective AR-REPLICATOR data path implementation will be compatible
with the following rules:
- The Selective AR-REPLICATORs will build two flood-lists:
1. Flood-list #1 - composed of ACs and overlay tunnels to the
remote nodes in the BD, always using the IR-IPs in the tunnel
destination IP addresses. Some of those overlay tunnels MAY
be flagged as non-BM receivers based on the BM flag received
from the remote nodes in the BD.
2. Flood-list #2 - composed of ACs, a Selective AR-LEAF-set and a
Selective AR-REPLICATOR-set, where:
+ The Selective AR-LEAF-set is composed of the overlay
tunnels to the AR-LEAFs that advertise a Leaf A-D route for
the local AR-REPLICATOR. This set is updated with every
Leaf A-D route received/withdrawn from a new AR-LEAF.
+ The Selective AR-REPLICATOR-set is composed of the overlay
tunnels to all the AR-REPLICATORs that send a Replicator-AR
route with L=1. The AR-IP addresses are used as tunnel
destination IP.
- When a Selective AR-REPLICATOR receives a BM packet on an AC, it
will forward the BM packet to its flood-list #1, skipping the non-
BM overlay tunnels.
- When a Selective AR-REPLICATOR receives a BM packet on an overlay
tunnel, it will check the destination and source IPs of the
underlay IP header and:
o If the destination IP matches its AR-IP and the source IP
matches an IP of its own Selective AR-LEAF-set, the AR-
REPLICATOR will forward the BM packet to its flood-list #2, as
long as the list of AR-REPLICATORs for the BD matches the
Selective AR-REPLICATOR-set. If the Selective AR-REPLICATOR-
set does not match the list of AR-REPLICATORs, the node reverts
back to non-selective mode and flood-list #1 is used.
o If the destination IP matches its AR-IP and the source IP does
not match any IP of its Selective AR-LEAF-set, the AR-
REPLICATOR will forward the BM packet to flood-list #2 but
skipping the AR-REPLICATOR-set.
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o If the destination IP matches its IR-IP, the AR-REPLICATOR will
use flood-list #1 but MUST skip all the overlay tunnels from
the flooding list, i.e. it will only replicate to local ACs.
This is the regular-IR behavior described in [RFC7432].
- In any case, non-BM overlay tunnels are excluded from flood-lists
and, also, source squelching is always done in order to ensure the
traffic is not sent back to the originating source. If the
encapsulation is MPLSoGRE (or MPLSoUDP) and the BD label is not
the bottom of the stack, the AR-REPLICATOR MUST copy the rest of
the labels when forwarding them to the egress overlay tunnels.
6.2. Selective AR-LEAF procedures
A Selective AR-LEAF chooses a single Selective AR-REPLICATOR per BD
and:
- Sends all the BD BM traffic to that AR-REPLICATOR and
- Expects to receive the BM traffic for a given BD from the same AR-
REPLICATOR.
In the example of Figure 1, we consider NVE1/NVE2/NVE3 as Selective
AR-LEAFs. NVE1 selects PE1 as its Selective AR-REPLICATOR. If that
is so, NVE1 will send all its BM traffic for BD-1 to PE1. If other
AR-LEAF/REPLICATORs send BM traffic, NVE1 will receive that traffic
from PE1. These are the differences in the behavior of a Selective
AR-LEAF compared to a non-selective AR-LEAF:
a. The AR-LEAF role selective capability SHOULD be an administrative
choice in any NVE/PE that is part of an AR-enabled BD. This
administrative option to enable AR-LEAF capabilities MAY be
implemented as a system level option as opposed to as per-BD
option.
b. The AR-LEAF MAY advertise a Regular-IR route if there are RNVEs
in the BD. The Selective AR-LEAF MUST advertise a Leaf A-D route
after receiving a Replicator-AR route with L=1. It is
RECOMMENDED that the Selective AR-LEAF waits for a AR-LEAF-join-
wait-timer (in seconds, default value is 3) before sending the
Leaf A-D route, so that the AR-LEAF can collect all the
Replicator-AR routes for the BD before advertising the Leaf A-D
route.
c. In a service where there is more than one Selective AR-
REPLICATORs the Selective AR-LEAF MUST locally select a single
Selective AR-REPLICATOR for the BD. Once selected:
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o The Selective AR-LEAF will send a Leaf A-D route including the
Route-key and IP-address-specific route-target of the selected
AR-REPLICATOR.
o The Selective AR-LEAF will send all the BM packets received on
the attachment circuits (ACs) for a given BD to that AR-
REPLICATOR.
o In case of a failure on the selected AR-REPLICATOR, another
AR-REPLICATOR will be selected and a new Leaf A-D update will
be issued for the new AR-REPLICATOR. This new route will
update the selective list in the new Selective AR-REPLICATOR.
In case of failure on the active Selective AR-REPLICATOR, it
is RECOMMENDED for the Selective AR-LEAF to revert to IR
behavior for a timer AR-REPLICATOR-activation-timer (in
seconds, default value is 3) to speed up the convergence.
When the timer expires, the Selective AR-LEAF will resume its
AR mode with the new Selective AR-REPLICATOR. The AR-
REPLICATOR-activation-timer MAY be the same configurable
parameter as in Section 5.2.
All the AR-LEAFs in a BD are expected to be configured as either
selective or non-selective. A mix of selective and non-selective AR-
LEAFs SHOULD NOT coexist in the same BD. In case there is a non-
selective AR-LEAF, its BM traffic sent to a selective AR-REPLICATOR
will not be replicated to other AR-LEAFs that are not in its
Selective AR-LEAF-set.
A Selective AR-LEAF will follow a data path implementation compatible
with the following rules:
- The Selective AR-LEAF nodes will build two flood-lists:
1. Flood-list #1 - composed of ACs and the overlay tunnel to the
selected AR-REPLICATOR (using the AR-IP as the tunnel
destination IP).
2. Flood-list #2 - composed of ACs and overlay tunnels to the
remote IR-IP Addresses.
- When an AR-LEAF receives a BM packet on an AC, it will check if
there is any selected AR-REPLICATOR. If there is, flood-list #1
will be used. Otherwise, flood-list #2 will.
- When an AR-LEAF receives a BM packet on an overlay tunnel, will
forward the BM packet to its local ACs and never to an overlay
tunnel. This is the regular IR behavior described in [RFC7432].
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7. Pruned-Flood-Lists (PFL)
In addition to AR, the second optimization supported by this solution
is the ability for the all the BD nodes to signal Pruned-Flood-Lists
(PFL). As described in section 3, an EVPN node can signal a given
value for the BM and U PFL flags in the IR Inclusive Multicast
Routes, where:
- BM is the Broadcast and Multicast flag. BM=1 means "prune-me"
from the BM flood-list. BM=0 means regular behavior.
- U is the Unknown flag. U=1 means "prune-me" from the Unknown
flood-list. U=0 means regular behavior.
The ability to signal these PFL flags is an administrative choice.
Upon receiving a non-zero PFL flag, a node MAY decide to honor the
PFL flag and remove the sender from the corresponding flood-list. A
given BD node receiving BUM traffic on an overlay tunnel MUST
replicate the traffic normally, regardless of the signaled PFL flags.
This optimization MAY be used along with the AR solution.
7.1. A PFL example
In order to illustrate the use of the solution described in this
document, we will assume that BD-1 in figure 1 is optimized-IR
enabled and:
- PE1 and PE2 are administratively configured as AR-REPLICATORs, due
to their high-performance replication capabilities. PE1 and PE2
will send a Replicator-AR route with BM/U flags = 00.
- NVE1 and NVE3 are administratively configured as AR-LEAF nodes,
due to their low-performance software-based replication
capabilities. They will advertise a Regular-IR route with type
AR-LEAF. Assuming both NVEs advertise all the attached VMs in
EVPN as soon as they come up and don't have any VMs interested in
multicast applications, they will be configured to signal BM/U
flags = 11 for BD-1.
- NVE2 is optimized-IR unaware; therefore it takes on the RNVE role
in BD-1.
Based on the above assumptions the following forwarding behavior will
take place:
1. Any BM packets sent from VM11 will be sent to VM12 and PE1. PE1
will forward further the BM packets to TS1, WAN link, PE2 and
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NVE2, but not to NVE3. PE2 and NVE2 will replicate the BM
packets to their local ACs but we will avoid NVE3 having to
replicate unnecessarily those BM packets to VM31 and VM32.
2. Any BM packets received on PE2 from the WAN will be sent to PE1
and NVE2, but not to NVE1 and NVE3, sparing the two hypervisors
from replicating unnecessarily to their local VMs. PE1 and NVE2
will replicate to their local ACs only.
3. Any Unknown unicast packet sent from VM31 will be forwarded by
NVE3 to NVE2, PE1 and PE2 but not NVE1. The solution avoids the
unnecessary replication to NVE1, since the destination of the
unknown traffic cannot be at NVE1.
4. Any Unknown unicast packet sent from TS1 will be forwarded by PE1
to the WAN link, PE2 and NVE2 but not to NVE1 and NVE3, since the
target of the unknown traffic cannot be at those NVEs.
8. AR Procedures for single-IP AR-REPLICATORS
The procedures explained in sections Section 5 and Section 6 assume
that the AR-REPLICATOR can use two local routable IP addresses to
terminate and originate NVO tunnels, i.e. IR-IP and AR-IP addresses.
This is usually the case for PE-based AR-REPLICATOR nodes.
In some cases, the AR-REPLICATOR node does not support more than one
IP address to terminate and originate NVO tunnels, i.e. the IR-IP and
AR-IP are the same IP addresses. This may be the case in some
software-based or low-end AR-REPLICATOR nodes. If this is the case,
the procedures in sections Section 5 and Section 6 MUST be modified
in the following way:
- The Replicator-AR routes generated by the AR-REPLICATOR use an AR-
IP that will match its IR-IP. In order to differentiate the data
plane packets that need to use IR from the packets that must use
AR forwarding mode, the Replicator-AR route MUST advertise a
different VNI/VSID than the one used by the Regular-IR route. For
instance, the AR-REPLICATOR will advertise AR-VNI along with the
Replicator-AR route and IR-VNI along with the Regular-IR route.
Since both routes have the same key, different RDs are needed in
each route.
- An AR-REPLICATOR will perform IR or AR forwarding mode for the
incoming Overlay packets based on an ingress VNI lookup, as
opposed to the tunnel IP DA lookup. Note that, when replicating
to remote AR-REPLICATOR nodes, the use of the IR-VNI or AR-VNI
advertised by the egress node will determine the IR or AR
forwarding mode at the subsequent AR-REPLICATOR.
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The rest of the procedures will follow what is described in sections
Section 5 and Section 6.
9. AR Procedures and EVPN All-Active Multi-homing Split-Horizon
This section extends the procedures for the cases where AR-LEAF nodes
or AR-REPLICATOR nodes are attached to the the same Ethernet Segment
in the BD. The case where one (or more) AR-LEAF node(s) and one (or
more) AR-REPLICATOR node(s) are attached to the same Ethernet Segment
is out of scope.
9.1. Ethernet Segments on AR-LEAF nodes
If VXLAN or NVGRE are used, and if the Split-horizon is based on the
tunnel IP SA and "Local-Bias" as described in [RFC8365], the Split-
horizon check will not work if there is an Ethernet-Segment shared
between two AR-LEAF nodes, and the AR-REPLICATOR changes the tunnel
IP SA of the packets with its own AR-IP.
In order to be compatible with the IP SA split-horizon check, the AR-
REPLICATOR MAY keep the original received tunnel IP SA when
replicating packets to a remote AR-LEAF or RNVE. This will allow AR-
LEAF nodes to apply Split-horizon check procedures for BM packets,
before sending them to the local Ethernet-Segment. Even if the AR-
LEAF's IP SA is preserved when replicating to AR-LEAFs or RNVEs, the
AR-REPLICATOR MUST always use its IR-IP as IP SA when replicating to
other AR-REPLICATORs.
When EVPN is used for MPLS over GRE (or UDP), the ESI-label based
split-horizon procedure as in [RFC7432] will not work for multi-homed
Ethernet-Segments defined on AR-LEAF nodes. "Local-Bias" is
recommended in this case, as in the case of VXLAN or NVGRE explained
above. The "Local-Bias" and tunnel IP SA preservation mechanisms
provide the required split-horizon behavior in non-selective or
selective AR.
Note that if the AR-REPLICATOR implementation keeps the received
tunnel IP SA, the use of uRPF (unicast Reverse Path Forwarding)
checks in the IP fabric based on the tunnel IP SA MUST be disabled.
9.2. Ethernet Segments on AR-REPLICATOR nodes
Ethernet Segments associated to one or more AR-REPLICATOR nodes
SHOULD follow "Local-Bias" procedures for EVPN all-active multi-
homing, as follows:
- For BUM traffic received on a local AR-REPLICATOR's AC, "Local-
Bias" procedures as in [RFC8365] SHOULD be followed.
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- For BUM traffic received on an AR-REPLICATOR overlay tunnel with
AR-IP as the IP DA, "Local-Bias" SHOULD also be followed. That
is, traffic received with AR-IP as IP DA will be treated as though
it had been received on a local AC that is part of the ES and will
be forwarded to all local ES, irrespective of their DF or NDF
state.
- BUM traffic received on an AR-REPLICATOR overlay tunnel with IR-IP
as the IP DA, will follow regular [RFC8365] "Local-Bias" rules and
will not be forwarded to local ESes that are shared with the AR-
LEAF or AR-REPLICATOR originating the traffic.
10. Security Considerations
The Security Considerations in [RFC7432] and [RFC8365] apply to this
document.
In addition, the procedures introduced by this document may bring
some new risks for the successful delivery of BM traffic. Unicast
traffic is not affected by this document. The forwarding of
Broadcast and Multicast (BM) traffic is modified though, and BM
traffic from the AR-LEAF nodes will be attracted by the existance of
AR-REPLICATORs in the BD. An AR-LEAF will forward BM traffic to its
selected AR-REPLICATOR, therefore an attack on the AR-REPLICATOR
could impact the delivery of the BM traffic using that node.
An implementation following the procedures in this document should
not create BM loops, since the AR-REPLICATOR will always forward the
BM traffic using the correct tunnel IP Destination Address that
indicates the remote nodes how to forward the traffic. This is true
in both, the Non-Selective and Selective modes defined in this
document.
The Selective mode provides a multi-staged replication solution,
where a proper configuration of all the AR-REPLICATORs will avoid any
issues. A mix of mistakenly configured Selective and Non-Selective
AR-REPLICATORs in the same BD could theoretically create packet
duplication in some AR-LEAFs, however this document provides a fall
back solution to Non-Selective mode in case the AR-REPLICATORs
advertised an inconsistent AR Replication mode.
Finally, the use of PFL as in Section 7, should be handled with care.
An intentional or unintentional misconfiguration of the BDs on a
given leaf node may result in the leaf not receiving the required BM
or Unknown unicast traffic.
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11. IANA Considerations
IANA has allocated the following Border Gateway Protocol (BGP)
Parameters:
- Allocation in the P-Multicast Service Interface Tunnel (PMSI
Tunnel) Tunnel Types registry:
Value Meaning Reference
0x0A Assisted-Replication Tunnel [This document]
- Allocations in the P-Multicast Service Interface (PMSI) Tunnel
Attribute Flags registry:
Value Name Reference
3-4 Assisted-Replication Type (T) [This document]
5 Broadcast and Multicast (BM) [This document]
6 Unknown (U) [This document]
12. Contributors
In addition to the names in the front page, the following co-authors
also contributed to this document:
Wim Henderickx
Nokia
Kiran Nagaraj
Nokia
Ravi Shekhar
Juniper Networks
Nischal Sheth
Juniper Networks
Aldrin Isaac
Juniper
Mudassir Tufail
Citibank
13. Acknowledgments
The authors would like to thank Neil Hart, David Motz, Dai Truong,
Thomas Morin, Jeffrey Zhang, Shankar Murthy and Krzysztof Szarkowicz
for their valuable feedback and contributions.
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14. References
14.1. Normative References
[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>.
[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>.
[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>.
[I-D.ietf-bess-evpn-bum-procedure-updates]
Zhang, Z., Lin, W., Rabadan, J., Patel, K., and A.
Sajassi, "Updates on EVPN BUM Procedures", draft-ietf-
bess-evpn-bum-procedure-updates-10 (work in progress),
September 2021.
14.2. Informative References
[RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
Uttaro, J., and W. Henderickx, "A Network Virtualization
Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
DOI 10.17487/RFC8365, March 2018,
<https://www.rfc-editor.org/info/rfc8365>.
Authors' Addresses
J. Rabadan (editor)
Nokia
777 Middlefield Road
Mountain View, CA 94043
USA
Email: jorge.rabadan@nokia.com
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S. Sathappan
Nokia
Email: senthil.sathappan@nokia.com
W. Lin
Juniper Networks
Email: wlin@juniper.net
M. Katiyar
Versa Networks
Email: mukul@versa-networks.com
A. Sajassi
Cisco Systems
Email: sajassi@cisco.com
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