BESS Workgroup J. Rabadan, Ed.
Internet Draft S. Sathappan
Intended status: Standards Track Nokia
W. Lin
Juniper
M. Katiyar
Versa Networks
A. Sajassi
Cisco
Expires: April 22, 2019 October 19, 2018
Optimized Ingress Replication solution for EVPN
draft-ietf-bess-evpn-optimized-ir-06
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 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.
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Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on April 22, 2019.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Conventions . . . . . . . . . . . . . . . . . . 4
3. Solution requirements . . . . . . . . . . . . . . . . . . . . . 5
4. EVPN BGP Attributes for optimized-IR . . . . . . . . . . . . . 6
5. Non-selective Assisted-Replication (AR) Solution Description . 9
5.1. Non-selective AR-REPLICATOR procedures . . . . . . . . . . 10
5.2. Non-selective AR-LEAF procedures . . . . . . . . . . . . . 11
5.3. RNVE procedures . . . . . . . . . . . . . . . . . . . . . . 12
5.4. Forwarding behavior in non-selective AR EVIs . . . . . . . 13
5.4.1. Broadcast and Multicast forwarding behavior . . . . . . 13
5.4.1.1. Non-selective AR-REPLICATOR BM forwarding . . . . . 13
5.4.1.2. Non-selective AR-LEAF BM forwarding . . . . . . . . 14
5.4.1.3. RNVE BM forwarding . . . . . . . . . . . . . . . . 14
5.4.2. Unknown unicast forwarding behavior . . . . . . . . . . 14
5.4.2.1. Non-selective AR-REPLICATOR/LEAF Unknown unicast
forwarding . . . . . . . . . . . . . . . . . . . . 15
5.4.2.2. RNVE Unknown unicast forwarding . . . . . . . . . . 15
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6. Selective Assisted-Replication (AR) Solution Description . . . 15
6.1. Selective AR-REPLICATOR procedures . . . . . . . . . . . . 15
6.2. Selective AR-LEAF procedures . . . . . . . . . . . . . . . 17
6.3. Forwarding behavior in selective AR EVIs . . . . . . . . . 18
6.3.1. Selective AR-REPLICATOR BM forwarding . . . . . . . . . 18
6.3.2. Selective AR-LEAF BM forwarding . . . . . . . . . . . . 19
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 . . . . . . . . . 23
10. Benefits of the optimized-IR solution . . . . . . . . . . . . 23
11. Security Considerations . . . . . . . . . . . . . . . . . . . 24
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
13.1 Normative References . . . . . . . . . . . . . . . . . . . 24
13.2 Informative References . . . . . . . . . . . . . . . . . . 25
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 25
15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
16. 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
part of the same EVPN Instance (EVI) use Ingress Replication (IR) or
PIM-based trees to transport the tenant's 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 (Broadcast,
Unknown unicast and Multicast 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
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networks where all the MAC and IP addresses are learnt 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 the 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:
i) Assisted-Replication (AR)
ii) 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 3.
Section 2 lists the requirements of the combined optimized-IR
solution, whereas sections 4 and 5 describe the Assisted-Replication
(AR) solution, and section 6 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
Regular-IR: Refers to Regular Ingress Replication, where the source
NVE/PE sends a copy to each remote NVE/PE part of the EVI.
AR-IP: IP address owned by the AR-REPLICATOR and used to
differentiate the ingress traffic that must follow the AR
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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
selective 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 EVI 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 (AD) route
VXLAN: Virtual Extensible LAN
GRE: Generic Routing Encapsulation
NVGRE: Network Virtualization using Generic Routing Encapsulation
GENEVE: Generic Network Virtualization Encapsulation
NVO: Network Virtualization Overlay
NVE: Network Virtualization Edge
VNI: VXLAN Network Identifier
EVI: EVPN Instance. An EVPN instance spanning the Provider Edge (PE)
devices participating in that EVPN
3. Solution requirements
The IR optimization solution specified in this document (optimized-IR
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hereafter) meets the following requirements:
a) The solution provides an IR optimization for BM (Broadcast and
Multicast) traffic, while preserving the packet order for unicast
applications, i.e., known and unknown unicast traffic should
follow the same path.
b) 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].
c) The solution is backwards compatible with existing NVEs using a
non-optimized version of IR. A given EVI can have NVEs/PEs
supporting regular-IR and optimized-IR.
d) 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 defined as follows:
0 1 2 3 4 5 6 7
+-+-+-+-+-+--+-+-+
|rsvd | T |BM|U|L|
+-+-+-+-+-+--+-+-+
Where a new type field (for AR) and two new flags (for PFL signaling)
are defined:
- T is the AR Type field (2 bits) that 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 PFL (Pruned-Flood-Lists) flags defined the desired behavior of
the advertising router for the different types of traffic:
+ BM= Broadcast and Multicast (BM) flag. BM=1 means "prune-me" from
the BM flooding list. BM=0 means regular behavior.
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+ U= Unknown 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 10 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 EVI/Ethernet Tag:
o Regular-IR route: in this route, Originating Router's IP Address,
Tunnel Type (0x06), MPLS Label, Tunnel Identifier and Flags MUST be
used as described in [RFC7432]. The Originating Router's IP Address
and Tunnel Identifier are set to an IP address that we denominate
IR-IP in this document.
o 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 as well as the Tunnel Identifier
are set to the same routable IP address that we denominate AR-IP
and SHOULD be different than the IR-IP for a given PE/NVE.
+ Tunnel Type = Assisted-Replication (AR). Section 11 provides the
allocated type value.
+ T (AR role type) = 01 (AR-REPLICATOR).
+ L (Leaf Information Required) = 0 (for non-selective AR) or 1
(for selective AR).
In addition, this document also uses the Leaf-AD route (RT-11)
defined in [EVPN-BUM] in case the selective AR mode is used. The
Leaf-AD 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
multicast traffic from a specific AR-REPLICATOR. It is only used for
selective AR and its fields are set as follows:
+ Originating Router's IP Address is set to the advertising IR-IP
(same IP used by the AR-LEAF in regular-IR routes).
+ Route Key is the "Route Type Specific" NLRI of the Replicator-AR
route for which this Leaf-AD route is generated.
+ The AR-LEAF constructs an IP-address-specific route-target as
indicated in [EVPN-BUM], by placing the IP address carried in the
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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-AD routes.
+ The leaf-AD 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 IR-IP of the advertising AR-LEAF. The PMSI
Tunnel attribute MUST carry a downstream-assigned MPLS label 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, part of the EVI, 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).
5. Non-selective Assisted-Replication (AR) Solution Description
The following figure illustrates an example NVO network where the
non-selective AR function is enabled. Three different roles are
defined for a given EVI: 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 multicast traffic to
'all' the NVE/PEs in the EVI except for the source NVE/PE.
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( )
(_ WAN _)
+---(_ _)----+
| (_ _) |
PE1 | PE2 |
+------+----+ +----+------+
TS1--+ (EVI-1) | | (EVI-1) +--TS2
|REPLICATOR | |REPLICATOR |
+--------+--+ +--+--------+
| |
+--+----------------+--+
| |
| |
+----+ VXLAN/nvGRE/MPLSoGRE +----+
| | IP Fabric | |
| | | |
NVE1 | +-----------+----------+ | NVE3
Hypervisor| TOR | NVE2 |Hypervisor
+---------+-+ +-----+-----+ +-+---------+
| (EVI-1) | | (EVI-1) | | (EVI-1) |
| LEAF | | RNVE | | LEAF |
+--+-----+--+ +--+-----+--+ +--+-----+--+
| | | | | |
VM11 VM12 TS3 TS4 VM31 VM32
Figure 1 Optimized-IR scenario
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 EVI 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 EVI. This administrative
option to enable AR-REPLICATOR capabilities MAY be implemented as
a system level option as opposed to as a per-MAC-VRF 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
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(AC). If the Regular-IR route is advertised, the AR Type field MAY
be set to AR-REPLICATOR.
c) The Replicator-AR and Regular-IR routes will be generated
according to section 3. The AR-IP and IR-IP used by the
Replicator-AR will be different routable IP addresses.
d) When a node defined as AR-REPLICATOR receives a 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.
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-
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 EVI. This administrative option to
enable AR-LEAF capabilities MAY be implemented as a system level
option as opposed to as per-MAC-VRF 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 the AR-LEAF, it is
RECOMMENDED the use of this flag for an easy operation and
troubleshooting of the EVI.
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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 (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 EVI), 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
EVI. This selection is a local decision and it does not have
to match other AR-LEAF's selection within the same EVI.
o An AR-LEAF MAY select more than one AR-REPLICATOR and do
either per-flow or per-EVI 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
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) 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. This will give the
AR-REPLICATOR some time to program the AR-LEAF nodes before the
AR-LEAF sends BM traffic.
5.3. RNVE procedures
RNVE (Regular Network Virtualization Edge node) is defined as an
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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 EVI. 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-AD routes (due to the IP-address-specific route-target).
This role provides EVPN with the backwards compatibility required in
optimized-IR EVIs. Figure 1 shows NVE2 as RNVE.
5.4. Forwarding behavior in non-selective AR EVIs
In AR EVIs, 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.
Section 4.4.1. describes the expected forwarding behavior for BM
traffic in nodes acting as AR-REPLICATOR, AR-LEAF and RNVE. Section
4.4.2. describes the forwarding behavior for unknown unicast traffic.
Note that known unicast forwarding is not impacted by this solution.
5.4.1. Broadcast and Multicast forwarding behavior
The expected behavior per role is described in this section.
5.4.1.1. Non-selective AR-REPLICATOR BM forwarding
The AR-REPLICATORs will build a flooding list composed of ACs and
overlay tunnels to remote nodes in the EVI. Some of those overlay
tunnels MAY be flagged as non-BM receivers based on the BM flag
received from the remote nodes in the EVI.
o 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.
o When an AR-REPLICATOR receives a BM packet on an overlay tunnel, it
will check the destination IP of the underlay IP header and:
- 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
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to the originating AR-LEAF.
- 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].
5.4.1.2. Non-selective AR-LEAF BM forwarding
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 EVI. The selection of more than one AR-
REPLICATOR is described in section 4.2. 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.
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].
5.4.1.3. RNVE BM forwarding
The RNVE is completely unaware of the AR-REPLICATORs, AR-LEAF nodes
and BM/U flags (that information is ignored). Its forwarding behavior
is the regular IR behavior described in [RFC7432]. Any regular non-AR
node is fully compatible with the RNVE role described in this
document.
5.4.2. Unknown unicast forwarding behavior
The expected behavior is described in this section.
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5.4.2.1. Non-selective AR-REPLICATOR/LEAF Unknown unicast forwarding
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 a flood-list composed of ACs
and overlay tunnels to the IR-IP Addresses of the remote nodes in the
EVI. 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 EVI.
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].
5.4.2.2. RNVE Unknown unicast forwarding
As described for BM traffic, the RNVE is completely unaware of the
REPLICATORs, LEAF nodes and BM/U flags (that information is ignored).
Its forwarding behavior is the regular IR behavior described in
[RFC7432], also for Unknown unicast traffic. Any regular non-AR node
is fully compatible with the RNVE role described in this document.
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 EVI-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 slightly 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
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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 EVI, as the AR
role itself. This administrative option MAY be implemented as a
system level option as opposed to as a per-MAC-VRF option.
b) Each AR-REPLICATOR will build a list of AR-REPLICATOR, AR-LEAF and
RNVE nodes (AR-LEAF nodes that sent only a regular-IR route are
accounted as RNVEs by the AR-REPLICATOR). 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 EVI context), the
rest of the AR-REPLICATORs will fall back to non-selective AR
mode.
b) The Selective AR-REPLICATOR MUST follow the procedures described
in section 4.1, 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 3.
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-AD route
with PE1's IP-address-specific route-target and NVE3
advertises a Leaf-AD route with PE2's IP-address-specific
route-target, PE1 MUST only add NVE1/NVE2 to its selective AR-
LEAF-set for EVI-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
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MUST NOT replicate the BM traffic to remote RNVEs). In other
words, 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
indication for the remote Selective AR-REPLICATOR that the
packet needs further replication to its AR-LEAFs.
6.2. Selective AR-LEAF procedures
A Selective AR-LEAF chooses a single Selective AR-REPLICATOR per EVI
and:
o Sends all the EVI BM traffic to that AR-REPLICATOR and
o Expects to receive the BM traffic for a given EVI 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 EVI-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 EVI. This
administrative option to enable AR-LEAF capabilities MAY be
implemented as a system level option as opposed to as per-MAC-VRF
option.
b) The AR-LEAF MAY advertise a Regular-IR route if there are RNVEs in
the EVI. The Selective AR-LEAF MUST advertise a Leaf-AD route
after receiving a Replicator-AR route with L=1. It is recommended
that the Selective AR-LEAF waits for a timer t before sending the
Leaf-AD route, so that the AR-LEAF receives all the Replicator-AR
routes for the EVI.
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 EVI. Once selected:
o The Selective AR-LEAF will send a Leaf-AD route including the
Route-key and IP-address-specific route-target of the selected
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AR-REPLICATOR.
o The Selective AR-LEAF will send all the BM packets received on
the attachment circuits (ACs) for a given EVI 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-AD 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 t to speed up the convergence. When the
timer expires, the Selective AR-LEAF will resume its AR mode
with the new Selective AR-REPLICATOR.
All the AR-LEAFs in an EVI 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 EVI. 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.
6.3. Forwarding behavior in selective AR EVIs
This section describes the differences of the selective AR forwarding
mode compared to the non-selective mode. Compared to section 4.4,
there are no changes for the forwarding behavior in RNVEs or for
unknown unicast traffic.
6.3.1. Selective AR-REPLICATOR BM forwarding
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 EVI, 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 EVI.
2) Flood-list #2 - composed of ACs, a Selective AR-LEAF-set and a
Selective AR-REPLICATOR-set, where:
o The Selective AR-LEAF-set is composed of the overlay tunnels
to the AR-LEAFs that advertise a Leaf-AD route for the local
AR-REPLICATOR. This set is updated with every Leaf-AD route
received/withdrawn from a new AR-LEAF.
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o 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:
- 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 EVI 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.
- 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.
- 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 EVI 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.
6.3.2. Selective AR-LEAF BM forwarding
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
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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].
7. Pruned-Flood-Lists (PFL)
In addition to AR, the second optimization supported by this solution
is the ability for the all the EVI 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= Broadcast and Multicast (BM) flag. BM=1 means "prune-me" from
the BM flood-list. BM=0 means regular behavior.
+ U= 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 EVI 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 EVI-1 in figure 1 is optimized-IR
enabled and:
o 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.
o 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
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come up and don't have any VMs interested in multicast
applications, they will be configured to signal BM/U flags = 11 for
EVI-1.
o NVE2 is optimized-IR unaware; therefore it takes on the RNVE role
in EVI-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
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 4 (Non-selective AR) and 5
(Selective AR) 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 4 and 5 must be modified in the following
way:
o 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
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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 for both routes.
o 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 described in sections 4 and 5. 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.
The rest of the procedures will follow what is described in sections
4 and 5.
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 Broadcast Domain. 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 DF
(Designated Forwarder) 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
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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:
o For BUM traffic received on a local AR-REPLICATOR's AC, "Local-
Bias" procedures as in [RFC8365] SHOULD be followed.
o 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.
o 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-LEF
or AR-REPLICATOR originating the traffic.
10. Benefits of the optimized-IR solution
A solution for the optimization of Ingress Replication in EVPN is
described in this document (optimized-IR). The solution brings the
following benefits:
o Optimizes the multicast forwarding in low-performance NVEs, by
relaying the replication to high-performance NVEs (AR-REPLICATORs)
and while preserving the packet ordering for unicast applications.
o Reduces the flooded traffic in NVO networks where some NVEs do not
need broadcast/multicast and/or unknown unicast traffic.
o It is fully compatible with existing EVPN implementations and EVPN
functions for NVO overlay tunnels. Optimized-IR NVEs and regular
NVEs can be even part of the same EVI.
o It does not require any PIM-based tree in the NVO core of the
network.
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11. Security Considerations
This section will be added in future versions.
12. IANA Considerations
IANA has allocated the following Border Gateway Protocol (BGP)
Parameters:
1) Allocation in the P-Multicast Service Interface Tunnel (PMSI
Tunnel) Tunnel Types registry:
Value Meaning Reference
0x0A Assisted-Replication Tunnel [This document]
2) 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]
13. References
13.1 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>.
[EVPN-BUM] Zhang et al., "Updates on EVPN BUM Procedures", draft-
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ietf-bess-evpn-bum-procedure-updates-04.txt, work in progress, June
2018.
13.2 Informative References
[RFC8365] Sajassi et al., "A Network Virtualization Overlay Solution
Using Ethernet VPN (EVPN)", RFC 8365, March, 2018.
14. 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
15. Acknowledgments
The authors would like to thank Neil Hart, David Motz, Dai Truong,
Thomas Morin, Jeffrey Zhang and Shankar Murthy for their valuable
feedback and contributions.
16. Authors' Addresses
Jorge Rabadan (Editor)
Nokia
777 E. Middlefield Road
Mountain View, CA 94043 USA
Email: jorge.rabadan@nokia.com
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Senthil Sathappan
Nokia
Email: senthil.sathappan@nokia.com
Mukul Katiyar
Versa Networks
Email: mukul@versa-networks.com
Wen Lin
Juniper Networks
Email: wlin@juniper.net
Ali Sajassi
Cisco
Email: sajassi@cisco.com
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