Optimized Ingress Replication Solution for Ethernet VPNs (EVPNs)Nokia777 Middlefield RoadMountain ViewCA94043United States of Americajorge.rabadan@nokia.comNokiasenthil.sathappan@nokia.comJuniper Networkswlin@juniper.netVersa Networksmukul@versa-networks.comCisco Systemssajassi@cisco.com
rtg
BESSAssisted ReplicationARAR-ReplicatorRNVEPruned Flood ListPFLPruned Flooding ListNetwork Virtualization Overlay (NVO) networks using Ethernet VPNs
(EVPNs) as their control plane may use trees based on ingress replication
or Protocol Independent Multicast (PIM) to convey the overlay Broadcast,
Unknown Unicast, or Multicast (BUM) traffic. PIM provides an efficient
solution that prevents sending multiple copies of the same packet over the
same physical link; however, it may not always be deployed in the
NVO network core. Ingress replication avoids the
dependency on PIM in the NVO network core.
While ingress replication 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 ingress
replication trees.Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
.
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Table of Contents
. Introduction
. Terminology and Conventions
. Solution Requirements
. EVPN BGP Attributes for Optimized Ingress Replication
. AR Procedures and EVPN All-Active Multihoming Split-Horizon
. Ethernet Segments on AR-LEAF Nodes
. Ethernet Segments on AR-REPLICATOR Nodes
. Security Considerations
. IANA Considerations
. References
. Normative References
. Informative References
Acknowledgements
Contributors
Authors' Addresses
IntroductionEthernet Virtual Private Networks (EVPNs) may be used as the control
plane for a Network Virtualization Overlay (NVO) network . Network Virtualization Edge (NVE) and Provider Edge
(PE) devices that are part of the same EVPN Broadcast Domain (BD) use
Ingress Replication (IR) or PIM-based trees to transport the tenant's
Broadcast, Unknown Unicast, or Multicast (BUM) traffic. In the ingress replication approach, the ingress NVE receiving a BUM
frame from the Tenant System (TS) will create as many copies of the
frame as the number of remote NVEs/PEs that are attached to the BD. Each of
those copies will be
encapsulated into an IP packet where the outer IP Destination Address
(IP DA) identifies the loopback of the egress NVE/PE. The IP fabric core
nodes (also known as spines) will simply route the IP-encapsulated BUM
frames based on the outer IP DA. If PIM-based trees are used instead of
ingress replication, the NVEs/PEs attached to the same BD will join a
PIM-based tree. The ingress NVE receiving a BUM frame will send a single
copy of the frame, encapsulated into an IP packet where the outer IP DA
is the multicast address that represents the PIM-based tree. The IP
fabric core nodes are part of the PIM tree and keep multicast state for
the multicast group, so that IP-encapsulated BUM frames can be routed to
all the NVEs/PEs that joined the tree.The two approaches are illustrated in . On the
left-hand side of the diagram, NVE1 uses ingress replication to send a BUM frame
(originated from Tenant System TS1) to the remote nodes attached to the
BD, i.e., NVE2, NVE3, and PE1. On the right-hand side, the
same example is depicted but using a PIM-based tree, i.e., (S1,G1),
instead of ingress replication. While a single copy of the tunneled BUM
frame is generated in the latter approach, all the routers in the fabric
need to keep multicast state, e.g., the spine keeps a PIM
routing entry for (S1,G1) with an Incoming Interface (IIF) and three
Outgoing Interfaces (OIFs).Ingress Replication vs. PIM-Based Trees in NVO Networks To WAN To WAN
^ ^
| |
+-----+ +-----+
+----------| PE1 |-----------+ +----------| PE1 |-----------+
| +--^--+ | | +--^--+ |
| | IP Fabric | | | IP Fabric |
| PE | | (S1,G1) |OIF to G1 |
| +----PE->+-----+ No State | | IIF +-----+ OIF to G1 |
| | +---2->|Spine|------+ | | +------>Spine|------+ |
| | | +-3->+-----+ | | | | +-----+ | |
| | | | 2 3 | | |PIM |OIF to G1| |
| | | |IR | | | | |tree | | |
|+-----+ +--v--+ +--v--+ | |+-----+ +--v--+ +--v--+ |
+| NVE1|---| NVE2|---| NVE3|-+ +| NVE1|---| NVE2|---| NVE3|-+
+--^--+ +-----+ +-----+ +--^--+ +-----+ +-----+
| | | | | |
| v v | v v
TS1 TS2 TS3 TS1 TS2 TS3
In NVO networks where PIM-based trees
cannot be used, ingress replication is the only option. Examples of
these situations are NVO networks where the
core nodes do not 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:
Broadcast traffic is greatly reduced due to the proxy
Address Resolution Protocol (ARP) and proxy Neighbor Discovery (ND)
capabilities supported by EVPNs on the NVEs. Some NVEs can even
provide Dynamic Host Configuration Protocol (DHCP) server functions
for the attached TSs, reducing the broadcast traffic even
further.
Unknown
unicast traffic is greatly reduced in NVO
networks where all the Media Access Control (MAC) and IP addresses from the TSs
are learned in the control plane.
Multicast applications are not used.
If the above assumptions are true for a given NVO network, then ingress replication provides a simple solution for
multi-destination traffic. However, 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 Top-of-Rack (ToR) 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 ingress
replication optimizations:
Assisted Replication (AR)
Pruned Flooding Lists (PFLs)
Assisted Replication consists of a set of procedures that allows the
ingress NVE/PE to send a single copy of a broadcast or multicast frame
received from a TS to the BD without the need
for PIM in the underlay. Assisted Replication defines the roles of
AR-REPLICATOR and AR-LEAF routers. The AR-LEAF is the ingress NVE/PE
attached to the TS. The AR-LEAF sends a single copy of a
broadcast or multicast packet to a selected AR-REPLICATOR that
replicates the packet multiple times to remote AR-LEAF or AR-REPLICATOR
routers and is therefore "assisting" the ingress AR-LEAF in delivering the
broadcast or multicast traffic to the remote NVEs/PEs attached to the
same BD. Assisted Replication can use a single
AR-REPLICATOR or two AR-REPLICATOR routers in the path between the
ingress AR-LEAF and the remote destination NVEs/PEs. The procedures that
use a single AR-REPLICATOR (the non-selective Assisted Replication solution)
are specified in , whereas describes how multi-stage replication, i.e., two
AR-REPLICATOR routers in the path between the ingress AR-LEAF and
destination NVEs/PEs, is accomplished (the selective Assisted Replication
solution). The procedures for Assisted Replication do not impact unknown
unicast traffic, which follows the same forwarding procedures as known
unicast traffic so that packet reordering does not occur.PFLs provide a method for the ingress NVE/PE to prune or
remove certain destination NVEs/PEs from a flooding list, depending on the
interest of those NVEs/PEs in receiving BUM traffic. As specified in , an NVE/PE builds a
flooding list for BUM traffic based on the next hops of the received EVPN
Inclusive Multicast Ethernet Tag routes for the BD. While
states that the flooding list is used for all BUM
traffic, this document allows pruning certain next hops from the list.
As an example, suppose an ingress NVE creates a flooding list with
next hops PE1, PE2, and PE3. If PE2 and PE3 did not signal any interest in
receiving unknown unicast traffic in their Inclusive Multicast Ethernet Tag
routes, when the ingress NVE receives an unknown unicast frame from a
TS, it will replicate it only to PE1. That is, PE2 and PE3 are
"pruned" from the NVE's flooding list for unknown unicast traffic.
PFLs can be used with ingress replication or
Assisted Replication and are described in .Both optimizations -- Assisted Replication and PFLs -- 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 the BGP attributes used in ; see for details.The Assisted Replication solution described in this document is
focused on NVO networks (hence its use of IP
tunnels). MPLS transport networks are out of scope for this document. The
PFLs solution MAY be used in NVO
and MPLS transport networks. lists the requirements of the combined
optimized ingress replication solution, whereas Sections
and describe the Assisted Replication solution
for non-selective and selective procedures, respectively. provides the PFLs solution.Terminology and ConventionsThe 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 when, and
only when, they appear in all capitals, as shown here.The following terminology is used throughout this document:
AR-IP:
Assisted Replication - IP. Refers to an IP address owned by the AR-REPLICATOR and used to
differentiate the incoming traffic that must follow the AR
procedures. The AR-IP is also used in the Tunnel Identifier and
Next Hop fields of the Replicator-AR route.
AR-LEAF:
Assisted Replication - LEAF. Refers to an NVE/PE that
sends all the BM traffic to an AR-REPLICATOR
that can replicate the traffic further on its behalf. An AR-LEAF is
typically an NVE/PE with poor replication performance
capabilities.
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 and local Attachment Circuits (ACs).
This document defines the control and data plane
procedures that an AR-REPLICATOR needs to follow.
AR-VNI:
Assisted Replication - VNI. Refers to a Virtual eXtensible Local Area Network (VXLAN) Network Identifier (VNI) advertised by the AR-REPLICATOR along with the
Replicator-AR route. It is used to identify the incoming packets
that must follow the AR procedures ONLY in the single-IP AR-REPLICATOR
case (see ).
Assisted Replication forwarding mode:
In the case of an AR-LEAF,
sending an AC Broadcast and Multicast (BM) packet to a single AR-REPLICATOR
with a tunnel destination address AR-IP. In the case of an AR-REPLICATOR, this means
sending a BM packet to a selected number of, or all of, the overlay tunnels
when the packet was previously received from an overlay tunnel.
BD:
Broadcast Domain, as defined in .
BD label:
Defined as the MPLS label that identifies the BD
and is advertised in Regular-IR or Replicator-AR routes, when
the encapsulation is MPLS over GRE (MPLSoGRE) or MPLS over UDP (MPLSoUDP).
BM traffic:
Refers to broadcast and multicast frames (excluding
unknown unicast frames).
DF and NDF:
Designated Forwarder and Non-Designated Forwarder.
These are roles defined in NVEs/PEs attached to multihomed TSs,
as per and .
ES and ESI:
Ethernet Segment and Ethernet Segment Identifier.
EVPN multihoming concepts as specified in .
EVI:
EVPN Instance. A group of Provider Edge (PE) devices
participating in the same EVPN service, as specified in .
GRE:
Generic Routing Encapsulation .
Ingress Replication forwarding mode:
Refers to the ingress
replication behavior explained in . In
this mode, an AC BM packet copy is sent to each remote PE/NVE
in the BD, and an overlay BM packet is sent only to the ACs
and not to other overlay tunnels.
IR-IP:
Ingress Replication - IP. Refers to the local IP address of an NVE/PE that is used for the ingress
replication signaling and procedures provided in .
Encapsulated incoming traffic with an outer destination IP address matching the
IR-IP will follow the procedures for ingress replication and not the
procedures for Assisted Replication. The IR-IP is also used in the
Tunnel Identifier and Next Hop fields of the Regular-IR route.
IR-VNI:
Ingress Replication - VNI. Refers to a VNI advertised along with the Inclusive Multicast
Ethernet Tag route for the ingress replication tunnel type.
MPLS:
Multi-Protocol Label Switching.
NVE:
Network Virtualization Edge .
NVGRE:
Network virtualization using Generic Routing
Encapsulation .
PE:
Provider Edge.
PMSI:
P-Multicast Service Interface. A conceptual interface for
a PE to send customer multicast traffic to all or some PEs in the
same VPN .
RD:
Route Distinguisher.
Regular-IR route:
An EVPN Inclusive Multicast Ethernet Tag route
that uses the ingress replication tunnel
type.
Replicator-AR route:
An EVPN Inclusive Multicast Ethernet Tag
route that is advertised by an AR-REPLICATOR to signal its
capabilities, as described in .
RNVE:
Regular NVE. Refers to an NVE that supports the procedures
provided in and does not support the procedures provided in
this document. However, this document defines procedures to
interoperate with RNVEs.
ToR switch:
Top-of-Rack switch.
TS and VM:
Tenant System and Virtual Machine. In this document,
TSs and VMs are the devices connected to
the ACs of the PEs and NVEs.
VNI:
VXLAN Network Identifier. Used in VXLAN tunnels.
VSID:
Virtual Segment Identifier. Used in NVGRE tunnels.
VXLAN:
Virtual eXtensible Local Area Network .
Solution RequirementsThe ingress replication optimization solution specified in this
document meets the following requirements:
The solution provides an ingress replication optimization for BM
traffic without the need for PIM while preserving the
packet order for unicast applications, i.e., unknown unicast traffic
should follow the same path as known unicast traffic. This
optimization is required in low-performance NVEs.
The solution reduces the flooded traffic in NVO
networks where some NVEs do not need broadcast/multicast and/or
unknown unicast traffic.
The solution is compatible with and
and has no impact on the Customer Edge (CE) procedures for
BM traffic. In particular, the solution supports the following EVPN
functions:
All-active multihoming, including the split-horizon and
DF functions.
Single-active multihoming, including the DF function.
Handling of multi-destination traffic and processing of
BM traffic as per .
The solution is backward compatible with existing NVEs using a
non-optimized version of ingress replication. A given BD can have
NVEs/PEs supporting regular ingress replication and optimized
ingress replication.
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.
EVPN BGP Attributes for Optimized Ingress ReplicationThe ingress replication optimization solution specified in this document
extends the Inclusive
Multicast Ethernet Tag routes and attributes described in so that an NVE/PE can
signal its optimized ingress replication capabilities.The Network Layer Reachability Information (NLRI) of the Inclusive Multicast Ethernet Tag route is shown in and is
used in this document without any modifications to its format. The PMSI
Tunnel Attribute's general format as provided in (which
takes it from ) is used in this document; only a
new tunnel type and new flags are specified, as shown in .EVPN Inclusive Multicast Ethernet Tag Route's NLRI +------------------------------------+
| RD (8 octets) |
+------------------------------------+
| Ethernet Tag ID (4 octets) |
+------------------------------------+
| IP Address Length (1 octet) |
+------------------------------------+
| Originating Router's IP Address |
| (4 or 16 octets) |
+------------------------------------+
PMSI Tunnel Attribute 0 1 2 3 4 5 6 7
+---------------------------------+ +--+--+--+--+--+--+--+--+
| Flags (1 octet) | -> |x |E |x | T |BM|U |L |
+---------------------------------+ +--+--+--+--+--+--+--+--+
| Tunnel Type (1 octet) | T = Assisted Replication Type
+---------------------------------+ BM = Broadcast and Multicast
| MPLS Label (3 octets) | U = Unknown (unknown unicast)
+---------------------------------+ x = unassigned
| Tunnel Identifier (variable) |
+---------------------------------+
The Flags field in is 8 bits long as per
. The Extension (E) flag was allocated by , and the Leaf
Information Required (L) flag was allocated by . This document defines the use of 4 bits of this Flags field:
Bits 3 and 4, which together form 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 Pruned Flooding Lists (PFLs) flags.The T field and PFLs flags are defined as follows:
T is the Assisted Replication Type field (2 bits), which defines
the AR role of the advertising router:
00 (decimal 0) = RNVE (non-AR support)
01 (decimal 1) = AR-REPLICATOR
10 (decimal 2) = AR-LEAF
11 (decimal 3) = RESERVED
The PFLs flags define the desired behavior of the
advertising router for the different types of traffic:
Broadcast and Multicast (BM) flag. BM = 1 means "prune me from
the BM flooding list". BM = 0 indicates regular behavior.
Unknown (U) flag. U = 1 means "prune me from the Unknown
flooding list". U = 0 indicates regular behavior.
The L flag (bit 7) is defined in
and will be used only in the
selective AR solution.
Please refer to for the IANA considerations
related to the PMSI Tunnel Attribute flags.In this document, the above Inclusive Multicast Ethernet Tag route
() and PMSI Tunnel Attribute () 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 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 MUST be
advertised with the T field set to 10 (AR-LEAF).
Replicator-AR route:
This route is used by the AR-REPLICATOR to
advertise its AR capabilities, with the fields set as follows:
Originating Router's IP Address MUST be set to an IP address
of the advertising router that is common to all the EVIs on the
PE (usually this is a loopback address of the PE).
The Tunnel Identifier and Next Hop fields SHOULD be set to the
same IP address as the Originating Router's IP Address field when
the NVE/PE originates the route -- that is, when the NVE/PE is
not an ASBR; see .
Irrespective of the values in the Tunnel Identifier and
Originating Router's IP Address fields, the ingress NVE/PE
will process the received Replicator-AR route and will use
the IP address setting in the Next Hop field to create IP tunnels to
the AR-REPLICATOR.
The Next Hop address is referred to as the AR-IP and MUST
be different from the IR-IP for a given PE/NVE, unless the
procedures provided in are followed.
Tunnel Type MUST be set to Assisted Replication Tunnel. provides the allocated type value.
T (Assisted Replication type) MUST be set to 01 (AR-REPLICATOR).
L (Leaf Information Required) MUST be set to 0 for
non-selective AR and MUST be set to 1 for selective AR.
An NVE/PE configured as an AR-REPLICATOR for a BD MUST advertise a
Replicator-AR route for the BD and MAY advertise a Regular-IR route. The
advertisement of the Replicator-AR route will indicate to the AR-LEAFs which
outer IP DA, i.e., which AR-IP, they need to use for IP-encapsulated BM
frames that use Assisted Replication forwarding mode. The AR-REPLICATOR
will forward an IP-encapsulated BM frame in Assisted Replication
forwarding mode if the outer IP DA matches its AR-IP but will forward
in Ingress Replication forwarding mode if the outer IP DA matches its
IR-IP.In addition, this document also uses the Leaf Auto-Discovery (Leaf
A-D) route defined in in cases where the
selective AR mode is used. An AR-LEAF MAY send a Leaf A-D route in
response to reception of a Replicator-AR route whose L flag is set. The
Leaf A-D route is only used for selective AR, and the fields
of such a route are set as follows:
Originating Router's IP Address is set to the advertising
router's IP address (the same IP address used by the AR-LEAF in Regular-IR
routes). The Next Hop address is set to the IR-IP, which SHOULD
be the same IP address as the advertising router's IP address,
when the NVE/PE originates the route, i.e., when the NVE/PE is
not an ASBR; see .
Route Key is the "Route Type Specific" NLRI of the
Replicator-AR route for which this Leaf A-D route is
generated.
The AR-LEAF constructs an IP-address-specific Route Target,
analogously to , by placing
the IP address carried in the Next Hop field of the received
Replicator-AR route in the Global Administrator field of the
extended community, with the Local Administrator field of this extended community
set to 0, and setting the Extended Communities attribute of the
Leaf A-D route to that extended community. The same
IP-address-specific import Route Target is auto-configured by
the AR-REPLICATOR that sent the Replicator-AR route, in order to
control the acceptance of the Leaf A-D routes.
The Leaf A-D route MUST include the PMSI Tunnel
Attribute with Tunnel Type set to Assisted Replication Tunnel (), T (Assisted Replication type) set to AR-LEAF, and
Tunnel Identifier set to the IP address 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 understands and processes the T
(Assisted Replication type) field in the PMSI Tunnel Attribute (Flags
field) of the routes and MUST signal the corresponding type
(AR-REPLICATOR or AR-LEAF type) according to its administrative choice.
An NVE/PE following this specification is not expected to set the
Assisted Replication Type field to decimal 3 (which is a RESERVED
value). If a route with the Assisted Replication Type field set to decimal 3 is received
by an AR-REPLICATOR or AR-LEAF, the router will process the route as a
Regular-IR route advertised by an RNVE.Each node attached to the BD may understand and process the BM/U
flags (PFLs flags). Note that these BM/U flags may be used
to optimize the delivery of multi-destination traffic; their use
SHOULD be an administrative choice and independent of the AR role. When
the PFL capability is enabled, the BM/U flags can be used
with the Regular-IR, Replicator-AR, and Leaf A-D routes.Non-optimized ingress replication NVEs/PEs will be unaware of the new
PMSI Tunnel Attribute flag definition as well as the new tunnel type
(AR), i.e., non-upgraded NVEs/PEs will ignore the information contained
in the Flags field or an unknown tunnel type (type AR in this case) for
any Inclusive Multicast Ethernet Tag route.Non-selective Assisted Replication (AR) Solution Description 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. The solution is called
"non-selective" because the chosen AR-REPLICATOR for a given flow MUST
replicate the BM traffic to all the NVEs/PEs in the BD except for the
source NVE/PE. NVO tunnels, i.e., IP tunnels,
exist among all the PEs and NVEs in the diagram. The PEs and NVEs in the
diagram have TSs or VMs connected to their
ACs.Non-selective AR Scenario
( )
(_ 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
In AR BDs, such as BD-1 in , BM
traffic between two NVEs may follow a different path than unicast
traffic. This solution recommends the replication of BM traffic through the
AR-REPLICATOR node, whereas unknown/known unicast traffic will be delivered
directly from the source node to the destination node without being
replicated by any intermediate node.Note that known unicast forwarding is not impacted by this solution,
i.e., unknown unicast traffic SHALL follow the same path as known unicast
traffic.Non-selective AR-REPLICATOR ProceduresAn AR-REPLICATOR is defined as an NVE/PE capable of replicating
incoming BM traffic received on an overlay tunnel to other overlay
tunnels and local 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 , PE1 and PE2
are defined as AR-REPLICATORs. The following considerations apply to
the AR-REPLICATOR role:
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 a per-BD
option.
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
ACs. If the Regular-IR route is advertised,
the Assisted Replication Type field of the Regular-IR route MUST
be set to 0.
The Replicator-AR and Regular-IR routes are
generated according to . The AR-IP and
IR-IP are different IP addresses owned by the AR-REPLICATOR.
When a node defined as an AR-REPLICATOR receives a BM
packet on an overlay tunnel, it will do a tunnel destination IP
address lookup and apply the following procedures:
If the destination IP address is the AR-REPLICATOR IR-IP
address, the node will process the packet normally as discussed in .
If the destination IP address 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 address will be an
IR-IP. This will indicate to the remote AR-REPLICATOR
that it MUST NOT replicate to overlay tunnels. The tunnel
source IP address used by the AR-REPLICATOR MUST be its IR-IP
when replicating to AR-REPLICATOR or AR-LEAF nodes.
An AR-REPLICATOR MUST follow a data path implementation
compatible with the following rules:
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 NVEs/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 address of the underlay
IP header and:
If the destination IP address 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 ingress replication behavior
described in .
If the destination IP address matches its AR-IP, the
AR-REPLICATOR MUST forward the BM packet to its flooding list
(ACs and overlay tunnels), excluding the non-BM overlay
tunnels. The AR-REPLICATOR will ensure that the traffic is not sent
back to the originating AR-LEAF.
If the encapsulation is MPLSoGRE or MPLSoUDP and the
received BD label that the AR-REPLICATOR advertised in the
Replicator-AR route is not at the bottom of the stack, the
AR-REPLICATOR MUST copy all the labels below the BD label
and propagate them when forwarding the packet to the egress
overlay tunnels.
The AR-REPLICATOR/LEAF nodes will build an unknown unicast
flooding 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.
When an AR-REPLICATOR/LEAF receives an unknown unicast
packet on an AC, it will forward the unknown
unicast packet to its flooding list, skipping the non-U overlay
tunnels.
When an AR-REPLICATOR/LEAF receives an unknown unicast
packet on an overlay tunnel, it will forward the unknown
unicast packet to its local ACs and never to
an overlay tunnel. This is the regular ingress replication
behavior described in .
Non-selective AR-LEAF ProceduresAn 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-LEAF
capability in the control plane and understands where the other roles
are located (AR-REPLICATORs and RNVEs). A given service can have zero,
one, or more AR-LEAF nodes. In ,
NVE1 and NVE3 (both residing in hypervisors) act as AR-LEAF nodes.
The following considerations apply to the AR-LEAF role:
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 a per-BD
option.
In this non-selective AR solution, the AR-LEAF MUST
advertise a single Regular-IR Inclusive Multicast Ethernet Tag route as described in
. The AR-LEAF SHOULD set the
Assisted Replication Type field to AR-LEAF. Note that although this
field does not affect the remote nodes when creating an EVPN destination
to the AR-LEAF, this field is useful from the standpoint of ease of
operation and troubleshooting of the BD.
In a BD where there are no AR-REPLICATORs due to
the AR-REPLICATORs being down or reconfigured, the AR-LEAF MUST
use regular ingress replication based on the remote Regular-IR
Inclusive Multicast Ethernet Tag routes as described in . This may happen in the following cases:
The AR-LEAF has a list of AR-REPLICATORs for the BD, but it
detects that all the AR-REPLICATORs for the BD are down (via
next-hop tracking in the IGP or some other detection
mechanism).
The AR-LEAF receives updates from all the former
AR-REPLICATORs containing a non-REPLICATOR AR type in the
Inclusive Multicast Ethernet Tag routes.
The AR-LEAF never discovered an AR-REPLICATOR for the
BD.
In a service where there are 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:
A single AR-REPLICATOR MAY be selected for all the BM
packets received on the AR-LEAF ACs for
a given BD. This selection is a local decision and does not
have to match other AR-LEAFs' selections within the same
BD.
An AR-LEAF MAY select more than one AR-REPLICATOR and do
either per-flow or per-BD load balancing.
In the case of failure of the selected AR-REPLICATOR, another
AR-REPLICATOR SHOULD be selected by the AR-LEAF.
When an AR-REPLICATOR is selected for a given flow or BD,
the AR-LEAF MUST send all the BM packets targeted 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 underlay destination IP address
MUST be the AR-IP advertised by the AR-REPLICATOR in the
Replicator-AR route.
An AR-LEAF MAY change the selection of AR-REPLICATOR(s)
dynamically due to an administrative or policy configuration
change.
AR-LEAF nodes SHALL send service-level BM control plane
packets, following the procedures for regular ingress replication. An
example would be IGMP, Multicast Listener Discovery (MLD), or PIM
packets, and, in
general, any packets using link-local scope multicast IPv4 or
IPv6 packets. The AR-REPLICATORs MUST NOT replicate these
control plane packets to other overlay tunnels, since they will
use the IR-IP address.
The use of an AR-REPLICATOR-activation-timer (in
seconds, with a default value of 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 the case of a newly added AR-REPLICATOR or if
an 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 needs to account for the
time it takes for the AR-LEAF Regular-IR Inclusive Multicast Ethernet Tag route
to get to the AR-REPLICATOR and be programmed. While the
AR-REPLICATOR-activation-timer is running, the AR-LEAF node will
use regular ingress replication.
If the AR-LEAF has selected an AR-REPLICATOR, whether
or not to change to a new preferred AR-REPLICATOR for the existing BM traffic flows is a matter of local policy.
An AR-LEAF MUST follow a data path implementation compatible
with the following rules:
The AR-LEAF nodes will build two flooding lists:
Flooding 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 item d. above and is a local
AR-LEAF decision.
Flooding 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:
If the AR-REPLICATOR-set is empty, the AR-LEAF MUST send
the packet to flooding list #2.
If the AR-REPLICATOR-set is NOT empty, the AR-LEAF MUST
send the packet to flooding list #1, where only one of the
overlay tunnels of the AR-REPLICATOR-set is used.
When an AR-LEAF receives a BM packet on an overlay tunnel, it
will forward the BM packet to its local ACs and
never to an overlay tunnel. This is the regular ingress
replication behavior described in .
AR-LEAF nodes process unknown unicast traffic in the same way
AR-REPLICATORS do, as described in .
RNVE ProceduresAn RNVE is defined as an
NVE/PE without AR-REPLICATOR or AR-LEAF capabilities that does ingress
replication as described in . 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 PMSI Tunnel Attribute) and the Leaf A-D routes (due to
the IP-address-specific Route Target).This role provides EVPNs with the backward compatibility required
in optimized ingress replication BDs. In , NVE2 acts as an RNVE.Selective Assisted Replication (AR) Solution Description is used to describe the selective AR
solution.Selective AR Scenario
( )
(_ 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-set-1 | |LEAF-set-1 | |LEAF-set-2 |
+--+-----+--+ +--+-----+--+ +--+-----+--+
| | | | | |
VM11 VM12 TS3 TS4 VM31 VM32
The solution is called "selective" because a given AR-REPLICATOR MUST
replicate the BM traffic to only the AR-LEAFs that requested the
replication (as opposed to all the AR-LEAF nodes) and MUST replicate the
BM traffic to the RNVEs (if there are any). The same AR roles as those defined in
Sections and are used here; however, the procedures are
different.The selective AR procedures create multiple AR-LEAF-sets in the EVPN
BD and build single-hop trees among AR-LEAFs of the same set
(AR-LEAF->AR-REPLICATOR->AR-LEAF) and two-hop trees among
AR-LEAFs of different sets
(AR-LEAF->AR-REPLICATOR->AR-REPLICATOR->AR-LEAF). Compared to
the selective solution, the non-selective AR method assumes that all the
AR-LEAFs of the BD are in the same set and always creates single-hop trees
among AR-LEAFs. While the selective solution is more efficient than the
non-selective solution in multi-stage IP fabrics, the trade-off is
additional signaling and an additional outer source IP address
lookup.The following subsections describe the differences in the procedures
for AR-REPLICATORs/LEAFs compared to the non-selective AR solution. There
are no changes applicable to RNVEs.Selective AR-REPLICATOR ProceduresIn our example in , PE1 and PE2 are
defined as selective AR-REPLICATORs. The following considerations
apply to the selective AR-REPLICATOR role:
The selective AR-REPLICATOR role SHOULD be an
administrative choice in any NVE/PE that is part of an
AR-enabled BD. This
administrative option MAY be implemented as a system-level option
as opposed to a per-BD option.
Each AR-REPLICATOR will build a list of AR-REPLICATOR, AR-LEAF,
and RNVE nodes. In spite of the "selective" administrative 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.
The selective AR-REPLICATOR MUST follow the procedures
described in , except for the following
differences:
The AR-REPLICATOR MUST have the L flag set to 1
when advertising 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
the third bullet of the procedures for Leaf A-D
routes in .
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 that 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 will only add
NVE1/NVE2 to its selective AR-LEAF-set for BD-1 and exclude
NVE3. Likewise, PE2 will only add NVE3 to its selective
AR-LEAF-set for BD-1 and exclude NVE1/NVE2.
When a node defined and operating as a selective
AR-REPLICATOR receives a packet on an overlay tunnel, it will
do a tunnel destination IP lookup, and if the destination IP
address 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
address 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 address (of the encapsulated
packet that arrived on the overlay tunnel) 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. When doing this replication, the tunnel
destination IP address is the AR-IP of the remote
selective AR-REPLICATOR. The tunnel destination address AR-IP
will indicate to the remote selective
AR-REPLICATOR that the packet needs further replication to
its AR-LEAFs.
A selective AR-REPLICATOR data path implementation MUST be
compatible with the following rules:
The selective AR-REPLICATORs will build two flooding lists:
Flooding 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.
Flooding 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 addresses.
Some of the overlay tunnels in the flooding lists MAY be flagged
as non-BM receivers based on the BM flag received from the remote
nodes in the routes.
When a selective AR-REPLICATOR receives a BM packet on an
AC, it MUST forward the BM packet to its
flooding 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:
If the destination IP address matches its AR-IP and the
source IP address matches an IP of its own selective
AR-LEAF-set, the AR-REPLICATOR MUST forward the BM packet to
its flooding list #2, unless some AR-REPLICATOR within the BD has
advertised L = 0. In the latter case, the node reverts to
Non-selective mode, and flooding list #1 MUST be used. Non-BM
overlay tunnels are skipped when sending BM packets.
If the destination IP address matches its AR-IP and the
source IP address does not match any IP address of its
selective AR-LEAF-set, the AR-REPLICATOR MUST forward the BM
packet to flooding list #2, skipping the AR-REPLICATOR-set.
Non-BM overlay tunnels are skipped when sending BM
packets.
If the destination IP address matches its IR-IP, the
AR-REPLICATOR MUST use flooding 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 ingress replication
behavior described in . Non-BM overlay
tunnels are skipped when sending BM packets.
In any case, the AR-REPLICATOR ensures that the traffic is not sent
back to the originating source. If the encapsulation is MPLSoGRE
or MPLSoUDP and the received BD label (the label that the
AR-REPLICATOR advertised in the Replicator-AR route) is not at the
bottom of the stack, the AR-REPLICATOR MUST copy the rest of the
labels when forwarding them to the egress overlay tunnels.
Selective AR-LEAF ProceduresA selective AR-LEAF chooses a single selective AR-REPLICATOR per BD
and:
Sends all the BD's BM traffic to that AR-REPLICATOR and
Expects to receive all the BM traffic for a given BD from the
same AR-REPLICATOR (except for the BM traffic from the RNVEs,
which comes directly from the RNVEs)
In the example in , 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-LEAFs/REPLICATORs send BM traffic,
NVE1 will receive that traffic from PE1. A selective AR-LEAF and a non-selective AR-LEAF behave differently, as follows:
The selective 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 a per-BD option.
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 wait for a period specified by an
AR-LEAF-join-wait-timer (in seconds, with a default value of 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. If the Replicator-AR route with L = 1
is withdrawn, the corresponding Leaf A-D route is
withdrawn too.
In a service where there is more than one selective
AR-REPLICATOR, the selective AR-LEAF MUST locally select a single
selective AR-REPLICATOR for the BD. Once selected:
The selective AR-LEAF MUST send a Leaf A-D route,
including the route key and IP-address-specific Route Target
of the selected AR-REPLICATOR.
The selective AR-LEAF MUST send all the BM packets received
on the ACs for a given BD to that
AR-REPLICATOR.
In the case of failure of the selected AR-REPLICATOR
(detected when the Replicator-AR route becomes infeasible as
a result of any of the underlying BGP mechanisms), 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 the case of failure of the active selective
AR-REPLICATOR, it is RECOMMENDED that the selective AR-LEAF
revert to ingress replication behavior for an
AR-REPLICATOR-activation-timer (in seconds, with a default value of
3) to mitigate the traffic impact. 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 the parameter discussed in .
A selective AR-LEAF MAY change the selection of AR-REPLICATOR(s)
dynamically due to an administrative or policy
configuration change.
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. If a
non-selective AR-LEAF is present, 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 MUST follow a data path implementation
compatible with the following rules:
The selective AR-LEAF nodes will build two flooding lists:
Flooding list #1:
Composed of ACs and the overlay tunnel to the selected
AR-REPLICATOR (using the AR-IP as the tunnel destination IP address).
Flooding list #2:
Composed of ACs and overlay tunnels to the remote IR-IP
addresses.
Some of the overlay tunnels in the flooding lists MAY be flagged
as non-BM receivers based on the BM flag received from the remote
nodes in the routes.
When an AR-LEAF receives a BM packet on an AC,
it will check to see if an AR-REPLICATOR was selected; if one is found,
flooding list #1 MUST be used. Otherwise, flooding list #2 MUST be used.
Non-BM overlay tunnels are skipped when sending BM packets.
When an AR-LEAF receives a BM packet on an overlay tunnel, it
MUST forward the BM packet to its local ACs and
never to an overlay tunnel. This is the regular ingress
replication behavior described in .
Pruned Flooding Lists (PFLs)In addition to AR, the second optimization supported by the ingress
replication optimization solution specified in this document
is the ability of all the BD nodes to signal PFLs. As described in , an EVPN node can signal
a given value for the BM and U PFLs flags in the
Regular-IR, Replicator-AR, or Leaf A-D routes, where:
BM is the Broadcast and Multicast flag. BM = 1 means "prune me
from the BM flooding list". BM = 0 indicates regular behavior.
U is the Unknown flag. U = 1 means "prune me from the Unknown
flooding list". U = 0 indicates regular behavior.
The ability to signal and process these PFLs flags
SHOULD be an administrative choice. If a node is configured to process
the PFLs flags, upon receiving a non-zero
PFLs flag for a route, an NVE/PE will add the
corresponding flag to the created overlay tunnel in the flooding list. When
replicating a BM packet in the context of a flooding list, the NVE/PE will
skip the overlay tunnels marked with the flag BM = 1, since the NVEs/PEs at
the end of those tunnels are not expecting BM packets. Similarly, when
replicating unknown unicast packets, the NVE/PE will skip the overlay
tunnels marked with U = 1.An NVE/PE not following this document or not configured for this
optimization will ignore any of the received PFLs flags.
An AR-LEAF or RNVE receiving BUM traffic on an overlay tunnel MUST
replicate the traffic to its local ACs, regardless of
the BM/U flags on the overlay tunnels.This optimization MAY be used along with the Assisted Replication
solution.Example of a Pruned Flooding ListIn order to illustrate the use of the PFLs solution, we will assume that BD-1 in is optimized ingress replication
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 that both NVEs advertise all of the attached VMs'
MAC and IP addresses in EVPNs as soon as they come up and
these NVEs do not have any VMs interested in
multicast applications, they will be configured to signal BM/U
flags = 11 for BD-1. That is, neither NVE1 nor NVE3 is interested
in receiving BM or unknown unicast traffic, since:
Their attached VMs (VM11, VM12, VM31, VM32) do not support
multicast applications.
Their attached VMs will not receive ARP Requests. Proxy ARP
on the remote
NVEs/PEs will reply to ARP Requests locally, and no other
broadcast traffic is expected.
Their attached VMs will not receive unknown unicast
traffic, since the VMs' MAC and IP addresses are always
advertised by EVPNs as long as the VMs are active.
NVE2 is optimized ingress replication unaware; therefore, it
takes on the RNVE role in BD-1.
Based on the above assumptions, the following forwarding behavior
will take place:
Any BM packets sent from VM11 will be sent to VM12
and PE1. PE1 will then forward the BM packets on to TS1, the WAN link,
PE2, and NVE2 but not to NVE3. PE2 and NVE2 will replicate the BM
packets to their local ACs, but NVE3 will be prevented from
having to replicate those BM packets to VM31 and
VM32 unnecessarily.
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.
Any unknown unicast packet sent from VM31 will be
forwarded by NVE3 to NVE2, PE1, and PE2 but not to NVE1. The solution
prevents unnecessary replication to NVE1, since the destination
of the unknown traffic cannot be NVE1.
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 NVE1 or
NVE3.
AR Procedures for Single-IP AR-REPLICATORSThe procedures explained in Sections and
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 provided in Sections and 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 ingress replication from the packets
that must use Assisted Replication 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 an AR-VNI along with the Replicator-AR route and an IR-VNI along
with the Regular-IR route. Since both routes have the same key,
different Route Distinguishers are needed in each route.
An AR-REPLICATOR will perform Ingress Replication forwarding mode or Assisted
Replication 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
whether Ingress Replication forwarding mode or Assisted Replication forwarding mode is used at
the subsequent AR-REPLICATOR.
The rest of the procedures will follow those described in
Sections and
.AR Procedures and EVPN All-Active Multihoming Split-HorizonThis section extends the procedures for the cases where two or more
AR-LEAF nodes are attached to the same ES and two or more
AR-REPLICATOR nodes are attached to the same ES in the BD.
The mixed case -- where an AR-LEAF node and an AR-REPLICATOR node are
attached to the same ES -- would require extended procedures
that are out of scope for this document.Ethernet Segments on AR-LEAF NodesIf a VXLAN or NVGRE is used and if the split-horizon is based on
the tunnel source IP address and "local bias" as described in , the split-horizon check will not work if
an ES is shared between two AR-LEAF nodes, and the
AR-REPLICATOR replaces the tunnel source IP address of the packets
with its own AR-IP.In order to be compatible with the source IP address split-horizon
check, the AR-REPLICATOR MAY keep the original received tunnel source IP
address 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 ES.
Even if the AR-LEAF's source IP address is preserved when replicating
to AR-LEAFs or RNVEs, the AR-REPLICATOR MUST always use its IR-IP as
the source IP address when replicating to other AR-REPLICATORs.When EVPNs are used for MPLSoGRE or MPLSoUDP, the ESI-label-based
split-horizon procedure provided in will not work
for multihomed ESs defined on AR-LEAF nodes.
Local bias is recommended in this case, as it is in the case of a VXLAN or
NVGRE as explained above. The local-bias and tunnel source IP address
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 source IP address, the use of unicast Reverse Path
Forwarding (uRPF) checks in the IP fabric based on the tunnel source IP
address MUST be disabled.Ethernet Segments on AR-REPLICATOR NodesAR-REPLICATOR nodes attached to the same all-active ES
will follow local-bias procedures
as follows:
For BUM traffic received on a local AR-REPLICATOR's AC,
local-bias procedures as provided in MUST be followed.
For BUM traffic received on an AR-REPLICATOR overlay tunnel
with AR-IP as the IP DA, local bias MUST also
be followed. That is, traffic received with AR-IP as the 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 ESs, 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 local-bias rules and will not be forwarded to
local ESs that are shared with the AR-LEAF or
AR-REPLICATOR originating the traffic.
In cases where the AR-REPLICATOR supports a single IP address,
the IR-IP and the AR-IP are the same IP address, as discussed in
. The received BUM traffic will be treated
as specified in item b above if the received VNI is the AR-VNI and as specified in item c if the VNI is the IR-VNI.
Security ConsiderationsThe security considerations in and apply to this document. The security considerations
related to the Leaf A-D route in apply too.In addition, the Assisted Replication method introduced by this
document may introduce some new risks that could affect the successful delivery of BM
traffic. Unicast traffic is not affected by Assisted Replication
(although unknown unicast traffic is affected by the procedures for PFLs). The forwarding of BM traffic is
modified, and BM traffic from the AR-LEAF nodes will be drawn toward
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. Also, an attack on the AR-REPLICATOR and any change to the advertised
AR type will modify the selections made by the AR-LEAF nodes. If no other
AR-REPLICATOR is selected, the AR-LEAF nodes will be forced to use
Ingress Replication forwarding mode, which will impact their
performance, since the AR-LEAF nodes are usually NVEs/PEs with poor
replication performance.This document introduces the ability of the AR-REPLICATOR to forward
traffic received on an overlay tunnel to another overlay tunnel. The
reader may determine that this introduces the risk of BM loops -- that is,
an AR-LEAF receiving a BM-encapsulated packet that the AR-LEAF
originated in the first place due to one or two AR-REPLICATORs
"looping" the BM traffic back to the AR-LEAF. Following the procedures provided in this
document will prevent these BM loops, since the AR-REPLICATOR will always
forward the BM traffic using the correct tunnel IP DA
(or the correct VNI in the case of single-IP AR-REPLICATORs), which instructs the
remote nodes regarding how to forward the traffic. This is true for both the
Non-selective and Selective modes defined in this document. However,
incorrect implementation of the procedures provided in this document may lead to
those unexpected BM loops.The Selective mode provides a multi-stage replication solution,
where proper configuration of all the AR-REPLICATORs will prevent 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 specifies a fallback solution -- falling back to Non-selective mode in cases where the AR-REPLICATORs
advertised an inconsistent AR mode.This document allows the AR-REPLICATOR to preserve the tunnel source IP
address of the AR-LEAF (as an option) when forwarding BM packets
from an overlay tunnel to another overlay tunnel. Preserving the AR-LEAF
source IP address makes the local-bias filtering procedures possible
for AR-LEAF nodes that are attached to the same ES. If the
AR-REPLICATOR does not preserve the AR-LEAF source IP address, AR-LEAF
nodes attached to all-active ESs will cause packet
duplication on the multihomed CE.The AR-REPLICATOR nodes are, by design, using more bandwidth than PEs or NVEs would use.
Certain network events or unexpected low performance may exceed the
AR-REPLICATOR's local bandwidth and cause service disruption.Finally, PFLs () should be
used with care. 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.IANA ConsiderationsIANA 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
RFC 9574
Allocations in the "P-Multicast Service Interface (PMSI) Tunnel Attribute Flags" registry:
Value
Name
Reference
3-4
Assisted Replication Type (T)
RFC 9574
5
Broadcast and Multicast (BM)
RFC 9574
6
Unknown (U)
RFC 9574
ReferencesNormative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Multicast in MPLS/BGP IP VPNsIn order for IP multicast traffic within a BGP/MPLS IP VPN (Virtual Private Network) to travel from one VPN site to another, special protocols and procedures must be implemented by the VPN Service Provider. These protocols and procedures are specified in this document. [STANDARDS-TRACK]BGP Encodings and Procedures for Multicast in MPLS/BGP IP VPNsThis document describes the BGP encodings and procedures for exchanging the information elements required by Multicast in MPLS/BGP IP VPNs, as specified in RFC 6513. [STANDARDS-TRACK]BGP MPLS-Based Ethernet VPNThis document describes procedures for BGP MPLS-based Ethernet VPNs (EVPN). The procedures described here meet the requirements specified in RFC 7209 -- "Requirements for Ethernet VPN (EVPN)".Registry and Extensions for P-Multicast Service Interface Tunnel Attribute FlagsThe BGP-based control procedures for Multicast Virtual Private Networks (MVPNs) make use of a BGP attribute known as the "P-Multicast Service Interface (PMSI) Tunnel" attribute. The attribute contains a one-octet "Flags" field. The purpose of this document is to establish an IANA registry for the assignment of the bits in this field. Since the "Flags" field contains only eight bits, this document also defines a new BGP Extended Community, "Additional PMSI Tunnel Attribute Flags", that can be used to carry additional flags for the "P-Multicast Service Interface (PMSI) Tunnel" attribute. This document updates RFC 6514.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.A Network Virtualization Overlay Solution Using Ethernet VPN (EVPN)This document specifies how Ethernet VPN (EVPN) can be used as a Network Virtualization Overlay (NVO) solution and explores the various tunnel encapsulation options over IP and their impact on the EVPN control plane and procedures. In particular, the following encapsulation options are analyzed: Virtual Extensible LAN (VXLAN), Network Virtualization using Generic Routing Encapsulation (NVGRE), and MPLS over GRE. This specification is also applicable to Generic Network Virtualization Encapsulation (GENEVE); however, some incremental work is required, which will be covered in a separate document. This document also specifies new multihoming procedures for split-horizon filtering and mass withdrawal. It also specifies EVPN route constructions for VXLAN/NVGRE encapsulations and Autonomous System Border Router (ASBR) procedures for multihoming of Network Virtualization Edge (NVE) devices.Updates to EVPN Broadcast, Unknown Unicast, or Multicast (BUM) ProceduresInformative ReferencesEncapsulating MPLS in IP or Generic Routing Encapsulation (GRE)Various applications of MPLS make use of label stacks with multiple entries. In some cases, it is possible to replace the top label of the stack with an IP-based encapsulation, thereby enabling the application to run over networks that do not have MPLS enabled in their core routers. This document specifies two IP-based encapsulations: MPLS-in-IP and MPLS-in-GRE (Generic Routing Encapsulation). Each of these is applicable in some circumstances. [STANDARDS-TRACK]Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 NetworksThis document describes Virtual eXtensible Local Area Network (VXLAN), which is used to address the need for overlay networks within virtualized data centers accommodating multiple tenants. The scheme and the related protocols can be used in networks for cloud service providers and enterprise data centers. This memo documents the deployed VXLAN protocol for the benefit of the Internet community.NVGRE: Network Virtualization Using Generic Routing EncapsulationThis document describes the usage of the Generic Routing Encapsulation (GRE) header for Network Virtualization (NVGRE) in multi-tenant data centers. Network Virtualization decouples virtual networks and addresses from physical network infrastructure, providing isolation and concurrency between multiple virtual networks on the same physical network infrastructure. This document also introduces a Network Virtualization framework to illustrate the use cases, but the focus is on specifying the data-plane aspect of NVGRE.Operational Aspects of Proxy ARP/ND in Ethernet Virtual Private NetworksThis document describes the Ethernet Virtual Private Network (EVPN) Proxy ARP/ND function augmented by the capability of the ARP/ND Extended Community. From that perspective, this document updates the EVPN specification to provide more comprehensive documentation of the operation of the Proxy ARP/ND function. The EVPN Proxy ARP/ND function and the ARP/ND Extended Community help operators of Internet Exchange Points, Data Centers, and other networks deal with IPv4 and IPv6 address resolution issues associated with large Broadcast Domains by reducing and even suppressing the flooding produced by address resolution in the EVPN network.AcknowledgementsThe authors would like to thank , , ,
, , , and for
their valuable feedback and contributions. Also, thanks to for his thorough review, which improved the quality of the document
significantly. ContributorsIn addition to the authors listed on the front page, the following people also contributed to this document and should be considered coauthors:NokiaNokiaJuniper NetworksJuniper NetworksJuniperCitibankAuthors' AddressesNokia777 Middlefield RoadMountain ViewCA94043United States of Americajorge.rabadan@nokia.comNokiasenthil.sathappan@nokia.comJuniper Networkswlin@juniper.netVersa Networksmukul@versa-networks.comCisco Systemssajassi@cisco.com