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SAVI in an EVPN network
draft-levyabegnoli-bess-evpn-savi-03

Document Type Active Internet-Draft (individual)
Authors Eric Levy-Abegnoli , Pascal Thubert , Ratko Kovacina
Last updated 2024-07-23
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draft-levyabegnoli-bess-evpn-savi-03
BESS                                                    E. Levy-Abegnoli
Internet-Draft                                                P. Thubert
Intended status: Informational                               R. Kovacina
Expires: 24 January 2025                                   Cisco Systems
                                                            23 July 2024

                        SAVI in an EVPN network
                  draft-levyabegnoli-bess-evpn-savi-03

Abstract

   Source Address Validation procedures have been specified in the SAVI
   Working Group and provide a set of mechanisms and state machines to
   verify Source Address ownership.  The main mechanisms are described
   in RFC6620 and RFC7513.

   RFC7432 and furthermore RFC9161 specify how an EVPN network could
   learn and distribute IP addressess.  RFC9161 describes a mechanism by
   which the PE can proxy some ND messages based on this information.

   In this document, we review how these two sets of specifications and
   underlying mechanisms can interact to provide Source Address
   Validation in an EVPN network.

Requirements Language

   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
   [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 24 January 2025.

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Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  SAVI background . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Deployment models . . . . . . . . . . . . . . . . . . . . . .   6
   5.  DHCP assigned addresses . . . . . . . . . . . . . . . . . . .   8
     5.1.  SAVI-DHCP background  . . . . . . . . . . . . . . . . . .   8
     5.2.  Interactions between RFC7513 and EVPN . . . . . . . . . .   9
   6.  SLAAC and other IPv6 addresses  . . . . . . . . . . . . . . .   9
     6.1.  SAVI-FCFS background  . . . . . . . . . . . . . . . . . .   9
     6.2.  Interactions between SAVI-FCFS and EVPN . . . . . . . . .   9
       6.2.1.  Address not found . . . . . . . . . . . . . . . . . .  11
       6.2.2.  Address found in EVPN table, remote not active  . . .  11
       6.2.3.  Address found in EVPN table, remote active  . . . . .  13
     6.3.  IPv4 address considerations . . . . . . . . . . . . . . .  14
     6.4.  Interaction with SAVNET considerations  . . . . . . . . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  15
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   11. Normative References  . . . . . . . . . . . . . . . . . . . .  15
   12. Informative References  . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   [RFC6620] describes a mechanism that provides Source Address
   Validation Improvements (SAVI) for IPv6 networks based the First Come
   First Serve (FCFS) principle, applicable to any type of IPv6
   addresses, including those assigned through IPv6 [RFC4291][RFC8200]
   Neighbor Discovery (ND) [RFC4861] Stateless Address Autoconfiguration
   (SLAAC) [RFC4862].  According to that specification, an IPv6 entry
   freshly snooped on a SAVI device needs to reach the “VALID“ state

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   before traffic sourced with it can be forwarded.

   Another SAVI specification, [RFC7513], describes a similar mechanism
   for addresses assigned by DHCPv6/DHCPv4 server.  Again, traffic
   sourced which such addresses can only be forwarded when the address
   state is “BOUND”.

   Section 10 of "BGP MPLS-Based Ethernet VPN" [RFC7432] (EVPN)
   indicates that a Provider Edge (PE) router may learn IP addresses and
   advertise them to other PEs.  EVPN allows PEs to execute a proxy ARP/
   ND function that is further detailed in "Operational Aspects of Proxy
   ARP/ND in Ethernet Virtual Private Network" [RFC9161].  According to
   section 3.2 of [RFC9161], IPv6 addresses should be learnt by snooping
   Neighbor Advertisements (NA), then advertised in an EVPN MAC/IP
   Advertisement route, and finally used on remote PEs to perform said
   proxy ARP/ND function.

   Assuming one would want to perform Source Address Validation in an
   EVPN network, two models can be deployed:

   1.  the SAVI function runs on SAVI switches not integrated with PEs

   2.  the SAVI function is integrated with the PEs

   These two models are reviewed in Section 4.  Corresponding
   interactions between SAVI and EVPN are reviewed as well in this
   document.

2.  Acronyms

   This document uses the following abbreviations:

   CE:  Customer Edge (router)
   DAD:  Duplicate Address Detection
   NA:  Neighbor Advertisement (message)
   ND:  Neighbor Discovery (protocol)
   NDP:  Neighbor Discovery Protocol
   NS:  Neighbor Solicitation (message)
   PE:  Provider Edge (router)
   VLAN:  Virtual Local Area Network
   VxLAN:  Virtual Extensible LAN
   EVPN:  Ethernet Virtual Private Network
   VTEP:  VXLAN Tunnel EndPoint (node)
   BGP:  Border Gateway Protocol
   SAVI-PE:  A PE that integrates SAVI functionality

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3.  SAVI background

   As specified in the [RFC7039] SAVI instance enforces the hosts' use
   of legitimate IP source addresses and to verify that the source
   address used in data packets actually belongs to the originator of
   the packet following three-step model:

   1.  Identify which IP source addresses are legitimate for a host,
       based on monitoring packets exchanged by the host.

   2.  Bind a legitimate IP address to the host's "binding anchor" which
       must be verifiable in every packet that the host sends.

   3.  Enforce that the IP source addresses in packets match the binding
       anchors to which they were bound.

   SAVI devices form a perimeter separating trusted and untrusted
   regions of a network.  As specified in [RFC6620] and [RFC7513], only
   validated addresses can inject traffic over the trusted perimeter.

                                protection perimeter
             +- - - - - - - - - - - - - - - - - - - - - - -+
             |                                             |
             |                trusted perimeter            |
             |    +- - - - - - - - - - - - - - - - - +     |
             |    |                                  |     |
             |    |                                  |     |
   +-------+ | +--+---+                           +--+---+ | +-------+
   |       | | | SAVI |                           | SAVI | | |       |
   |Client | | |      |     L2-Network            |      | | |Client |
   |       | | |device|                           |device| | |       |
   +-------+ | +--+---+                           +--+---+ | +-------+
             |    |                                  |     |
             |    +- - - - - - - - - - - - - - - - - +     |
             |                                             |
             +- - - - - - - - - - - - - - - - - - - - - - -+

                           Figure 1: SAVI network

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   According to [RFC6620], any address, used as the source of a packet
   or showing up as a target of a Neighbor Advertisement (NA) or a
   target of a DAD Neighbor Solicitation (NS), which is not locally
   known and validated, is treated as a TENTATIVE address.  Validation
   process is initiated with a DAD NS (Duplicate Address Detection
   Neighbor Solicitation) message with this address in the target field
   originated by the SAVI device and broadcasted to any validated or
   trusted port.  A response received implies a duplication and/or IP
   theft [B] and on the contrary, no response allows to progress the
   state of the address from TENTATIVE to VALID [A].

  +-------+       +---------+             +---------+         +-------+
  |Client1|       | SAVI1   |             | SAVI2   |         |Client2|
  |       |       |         |             |         |         |       |
  +-----+-+       +---------+             +---------+         +--+----+
        |               |                       |                |
        |               |                       |                |
   (*)  |data, src=IP   |                       |IP: VALID       |
        +-------------->|IP not found           |                |
        |               |                       |                |
        |   IP:TENTATIVE|                       |                |
        |               |                       |                |
        |               | l2-multicast DAD NS   |                |
        |               | target=IP             |                |
  +-    |               +---------------------->|DAD NS          |
  |     |               |                       +--------------->|
  A     |      wait TENT_LT                     |                |
  |     |               |                       |                |
  |     |               |                       |                |
  |     |      IP: VALID|                       |IP: NO_BIND     |
  +-    |               |                       |                |

                            DAD NS
  +-    |               +---------------------->|DAD NS          |
  |     |               |        NA, target=IP  +--------------->|
  B     |               |<---------------------------------------|
  |     |               |                       |                |
  |     |               |                       |                |
  |     |      IP: NO_BIND                      |IP: VALID       |
  +-    |      Theft logging                    |                |

 (*) Any packet, including a DAD. For DAD and NA, src is found in target
 field

                          Figure 2: SAVI flow

   Note that a SAVI device stores only local entries (client facing)

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   Sequence goes like this for A:

   1.  Data sourced with S is received on the ingress SAVI instance.  An
       entry for S is created in TENTATIVE state.

   2.  A DAD is built with target=S and broadcasted to all SAVI
       instances.

   3.  Only instances that have the entry "S" in VALID state or trusted
       ports forward the DAD.

   4.  In the absence of a response from Client, the state of the "S"
       entry at the ingress SAVI progresses to VALID.

   For B, after step 3 Client responds to DAD with an NA (dst=all
   nodes).

   5.  Upon receiving the NA, the ingress SAVI instance move the entry
       to NO_BIND and does not allow traffic from this source to be
       forwarded.

   As described in step 3, only instances that have the entry "S" in
   VALID state or trusted ports forward the DAD.

4.  Deployment models

   In model 1, a SAVI device is inserted between client (host or CE) and
   PE (or VTEP).  This first model is straight forward and does not
   require any additional specification.  It is presented in Figure 3.

   The SAVI devices operate as a verification perimeter between
   untrusted clients (CEs or Hosts) and PEs (or VTEPs).  As specified in
   [RFC6620] and [RFC7513], only validated addresses can inject traffic
   over the trusted perimeter.  The mechanisms to validate addresses are
   specified in these two RFCs.  Note that IPv6 DAD NS (IP source is set
   to the unspecified address, see section section-2.5.2 of [RFC4291] ),
   used by SAVI for validation, can still be forwarded by EVPN but are
   not used by EVPN proxy for learning.  Therefore, as long as an
   address is not validated by SAVI, it remains unknown by EVPN.

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                                protection perimeter
             +- - - - - - - - - - - - - - - - - - - - - - -+
             |                                             |
             |                trusted perimeter            |
             |            +- - - - - - - - - -+            |
             |            |                   |            |
             |            |    L3 NETWORK     |            |
             |            |  VTEP        VTEP |            |
   +-------+ | +------+  ++------+     +------++  +------+ | +-------+
   |       | | | SAVI |  |       |     |       |  | SAVI | | |       |
   |HOST/CE| | |      |  |EVPN/PE|     |EVPN/PE|  |      | | |HOST/CE|
   |       | | |device|  |       |     |       |  |device| | |       |
   +-------+ | +------+  ++------+     +------++  +------+ | +-------+
             |            |                   |            |
             |            |                   |            |
             |            |                   |            |
             |            |                   |            |
             |            +- - - - - - - - - -+            |
             |                                             |
             |                                             |
             +- - - - - - - - - - - - - - - - - - - - - - -+

                        Figure 3: Deployment model 1

   In this model, the SAVI device and the PE/VTEP can also be colapsed
   into the same box referenced as a SAVI-PE.  The injection happens
   over an API between SAVI instance and EVPN rather than over a
   physical wire.  Furthermore, only validated sources are learnt per
   section 3.2 of [RFC9161].

   In model 2, SAVI Instance is integrated with te EVPN PE/VTEP, It is
   presented in Figure 4.  In this model it is possible and even
   desirable to leverage the knowledge of remote IP entries stored in
   the VTEP EVPN tables to make SAVI validation process more efficient.

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                                protection perimeter
             +- - - - - - - -  - - - -  - - - - - -- - -- - +
             |                                              |
             |                trusted perimeter             |
             |            +- - - -- - - - - - -+            |
             |            |                    |            |
             |            |    L3 NETWORK      |            |
             |    SAVI-PE |                    | SAVI-PE    |
   +-------+ | +--------+-+------+      +------+-+--------+ | +-------+
   |       | | |SAVI    |        |      |        | SAVI   | | |       |
   |HOST/CE| | |        |  EVPN  |      | EVPN   |        | | |HOST/CE|
   |       | | |instance|        |      |        |instance| | |       |
   +-------+ | +--------+-+------+      +------+-+--------+ | +-------+
             |            |                    |            |
             |            |                    |            |
             |            |                    |            |
             |            |                    |            |
             |            +- - - - ---- - - - -+            |
             |                                              |
             |                                              |
             +- - - - - - - - - - - -   - - - - - - - - - - +
                                protection perimeter

                        Figure 4: Deployment model 2

   The next section review interactions between SAVI and EVPN for
   different type of addresses

5.  DHCP assigned addresses

5.1.  SAVI-DHCP background

   The "SAVI Solution for DHCP" [RFC7513] specification describes a
   mechanism that provides source address validation for IPv6 networks
   where addresses are assigned by DHCPv6 server.  The address
   validation is achieved by snooping DHCPv6 address assignments, which
   is known as DHCP Snooping, or validating discovered address with the
   DHCP server which is described as Data Snooping process.  Both
   processes are described in detail in [RFC7513].

   During DHCP Snooping process and according to associated state
   machine, an IP entry freshly snooped on a SAVI device progresses from
   NO_BIND to BOUND.

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5.2.  Interactions between RFC7513 and EVPN

   The whole DHCP address assignment procedure is performed using IPv6
   Link-Local addresses, which are expected to be VALID prior to the
   beginning of this process.  The DHCP server or relay can then be
   located anywhere in the EVPN network without the DHCP messages being
   blocked by SAVI.  EVPN itself does not learn from DHCP, so until the
   address is assigned, DAD completed and the host have sent an NA
   (response to a lookup or unsolicited NA), EVPN is not aware of the
   assigned address.  After the NA is sent, the address can be learnt by
   EVPN, stored locally by the EVPN proxy-ND, and distributed by BGP per
   [RFC9161].

   Source validation of DHCP assigned addresses in EVPN is described in
   "EVPN First Hop Security" [I-D.sajassi-bess-evpn-first-hop-security]

6.  SLAAC and other IPv6 addresses

6.1.  SAVI-FCFS background

   According to [RFC6620], any address, used as the source of a packet
   or showing up as a target of a Neighbor Advertisement (NA) or a
   target of a DAD Neighbor Solicitation (NS), which is not locally
   known and validated, is treated as a TENTATIVE address and a DAD NS
   (Duplicate Address Detection Neighbor Solicitation) message with this
   address in the target field is originated by the SAVI device and
   broadcasted to any validated or trusted port.  A response received
   implies a duplication and/or IP theft and on the contrary, no
   response allow to progress the state of the address from TENTATIVE to
   VALID.

6.2.  Interactions between SAVI-FCFS and EVPN

   Main interactions are listed below:

   *  Sources not validated by SAVI are not learnt nor distributed by
      EVPN: SAVI does not allow NA to be forwarded (model 1) or signaled
      (model 2) to EVPN.

   *  During the validation process for a Source, SAVI (ingress)
      originates a broadcast DAD, with target set to "Source" and
      forwards (model 1) or signals (model 2) it to EVPN, which delivers
      it to remote SAVI devices (over the wire or an API).  Only SAVI
      devices that have a local validated entry or a trusted interface
      forward the DAD to enable the target to defend itself.

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   *  In case a response is sent by one of the DAD recipients, it is a
      broadcast NA (to "all-nodes"), processed by SAVI (egress).  The
      source is expected to be a SAVI validated source, and as such,
      delivered from (egress) SAVI to EVPN for delivery to all VTEPs and
      finally to (ingress) SAVI to complete the validation process of
      the target "Source".

   *  The first NA sent by this Source triggers EVPN proxy learning and
      EVPN distribution to all VTEPs per [RFC9161].

   *  Important to note that the Duplicate IP Detection nechanism as
      described in section 3.7 of [RFC9161] would not be required if the
      EVPN PE carries out the SAVI procedures, since SAVI will prevent
      duplicate IP addresses from being learned and signaled to EVPN in
      the first place, and would optimize overall mechanism.

   In model 2 where SAVI is co-located with EVPN table, upon starting
   the validation process for an address, SAVI MAY perform a lookup into
   EVPN table, where entry can be 1) not found, 2) local or 3) remote.

   If the entry is local, this is an error as it is expected only VALID
   entries should be learnt by EVPN ND proxy.  The entry in the EVPN
   table MUST be deleted.

   Other cases are described in the next sections

   As described in [RFC6620], when validating a source address that is
   not known in the local SAVI table, a multicast DAD NS message is sent
   to all remote SAVI instances to check for the presence of this
   address on any of these instances.  This process can be optimized by
   leveraging the content of EVPN tables on VTEPs and "unicast-forward"
   the DAD to the known address owner, if any, more in [RFC6085].

   Depending on the presence of the address in the EVPN table and if
   present, whether the address is active or not, there are three
   possible scenarios as described below.

   1.  Address not found in EVPN table.

   2.  Address found in EVPN table, remote not active.

   3.  Address found in EVPN table, remote active.

   It is important to note that EVPN table is simply a "helper" for SAVI
   verification.  It may happen that the entry is not present in the
   EVPN table due to following reasons:

   *  Race condition (BGP did not converge yet for that entry).

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   *  EVPN decided not to distribute it (that may be the case for IPv6
      Link-Local addresses on some implementations).

   *  The entry has not been detected in the network yet.

   If the entry is not present in the EVPN table and not present in the
   SAVI table, the verification will fallback on sending a multicast
   (l2-broadcast) packet to all remote SAVI-PEs.

   Similarly, in the case the EVPN lookup for the IP returns a local
   entry, SAVI will also fallback on broadcasting the DAD NS used for
   verification to all remote SAVI-PEs.  This may happen if EVPN
   installs the entry for IP before SAVI get a chance to initiate the
   verification process, which could be the case in "loose-mode"
   described below.

6.2.1.  Address not found

   Since the source address that is being validated by SAVI process
   might not be present in the EVPN table for reasons described above,
   it means it cannot be moved to VALID state directly without
   performing validation as per [RFC6620].  It will be created as
   TENTATIVE in SAVI, and the verification will fallback on sending a
   multicast (l2-broadcast) packet to all remote SAVI-PEs.

   In the case when entry is not present in the EVPN table due to race
   condition or entry is not distributed by the EVPN, multicast NS DAD
   will be converted to unnicast on remote SAVI-PEs before forwarding to
   the target.  In the case when entry is not detected in the network,
   multicast NS DAD will be stopped at remote SAVI-PEs.

   Note that to prevent race condition where a host is VALID in the
   local SAVI instance but not yet present in the EVPN table, SAVI MAY
   signal the entry to EVPN as soon as it becomes VALID.

6.2.2.  Address found in EVPN table, remote not active

   When the source address that is being validated by SAVI process is
   present in the EVPN table, then the multicast NS DAD sent by SAVI can
   be "unicast-forwarded" per section 3.4.  "Unicast-Forward Sub-
   function" of [RFC9161].

   If the address is no longer active on the remote location, there will
   be no response and the validation process will follow the steps as
   specified in [RFC6620] to move the entry to VALID state.  Once the
   entry is in VALID state, the traffic received from that address will
   be forwarded into EVPN network and the IP address will be learned by
   the EVPN.  This is shown in Figure 5

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   SAVI instance MAY signal the entry to EVPN as soon as it becomes
   VALID.

   Note than, by default, waiting "TENT_LT" (TIMEOUT is TENTATIVE
   lifetime - default is 500ms) before moving entry to VALID state will
   delay mobility by this amount of time.

   Until validation is complete, traffic sourced from IP will be
   blocked.  It is also expected that EVPN will start the mobility
   procedure only at the end of the validation (after TENT_LT) process.
   This delay can however be improved in some cases.

   If the MACs (bound to IP) are the same on both locations, the EVPN
   MAC mobility procedure may start immediately after detection of the
   MAC at the new location, and traffic from the IP can be allowed
   "optimistically", to the exception of ARP/ND/DHCP messages that could
   change the status-quo (mac, dhcp lease, etc.).  See case 1 in the
   figure below.  This is sometimes referred to as "loose mode" as
   opposed to "strict mode" (nothing allowed till validation is
   complete).

   By doing so, traffic will resume to new location as soon as BGP has
   re-converged, and in case of an IP-theft, mobility procedure and/or
   SAVI validation (whichever completes first) will re-establish the
   previous situation (case 2 in the figure below).

   If the MAC bound to the IP is different from the one already known,
   the MAC will be advertised immediately, but not the IP which will be
   delayed by TENT_LT.  In this case, traffic from the IP or ARP/ND
   traffic announcing the MAC change should also be delayed.

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                    local PE             Remote PE
   +------+       +---------+             +---------+         +------+
   | HOST |       | SAVI-PE |             | SAVI-PE |         | HOST |
   |      |       |         |             |         |         |      |
   +----+-+       +---------+             +---------+         +--+---+
        |               |                       |                |
        |               |                       |                |
       (1)data, src=IP  |                       |IP: VALID       |
        +-------------->|IP:REMOTE      IP:LOCAL|                |
        |               |                       |                |
        |   IP:TENTATIVE|                       |                |
        |               |                       |                |
        |     IP:REMOTE |                       |                |
        |     found in  |                       |                |
        |     EVPN table|                       |                |
        |               |                       |                |
        |               |  (2)l2-unicast DAD NS |                |
        |               |     target=IP         |                |
        |               +---------------------->|(3)DAD NS       |
        |               |                       +--------------->|
        |      wait TENT_LT                     |                |
        |               |                       |                |
        |               |                       |                |
        |      IP: VALID|                       |                |
        |               |                       |                |
        |               | IP: LOCAL             |IP:NO_BIND      |
        |               | in EVPN table         |                |
        |               |                       |                |
        |               +--IP BGP advertized->  |                |
        |               |              IP:REMOTE|                |

                 Figure 5: Remote not responding - Mobility

6.2.3.  Address found in EVPN table, remote active

   As in previous section, local SAVI sends the multicast NS DAD to the
   known (by EVPN, as a remote entry) target but this time, the target
   responds with a multicast NA.  The validation process will follow the
   steps as specified in [RFC6620] and move the entry to NO_BIND state.
   Any NA received on this local SAVI instance from the validating port
   will not be signalled to EVPN and will not be learnt by EVPN ND
   proxy.  This is a IP duplication / theft use case and should be
   signalled through logging or by triggering an alarm.

   This is shown in Figure 6

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                    local PE             Remote PE
   +------+       +---------+             +---------+         +------+
   | HOST |       | SAVI-PE |             | SAVI-PE |         | HOST |
   |      |       |         |             |         |         |      |
   +----+-+       +-----+---+             +-----+---+         +--+---+
        |               |                       |                |
        |               |                       |                |
        | src=IP        |                       |IP: VALID       |
        +-------------->|IP:REMOTE      IP:LOCAL|                |
        |               |                       |                |
        |   IP:TENTATIVE|                       |                |
        |               |                       |                |
        |     IP:REMOTE |                       |                |
        |     found in  |                       |                |
        |     EVPN table|                       |                |
        |               |                       |                |
        |               |  (2)l2-unicast DAD NS |                |
        |               |     target=IP         |                |
        |               +---------------------->|(3)DAD NS       |
        |               |                       +--------------->|
        |               |                       |            NA  |
        |               |                       |<---------------|
        |               |<----------------------| allowed        |
        |    IP:NO_BIND |                       |                |
        |    Theft signalled                    |                |

                     Figure 6: Remote active - IP theft

6.3.  IPv4 address considerations

   While [RFC6620] does not mention IPv4, a very similar mechanism as
   the one described for IPv6 addresses could be used for IPv4.  NS DAD
   is simply replaced by ARP ACD (Address Conflict Detection) as
   specified in [RFC5227] in all previous diagrams.

6.4.  Interaction with SAVNET considerations

   The Source Address Validation Architecture (SAVA) [RFC5210] proposes
   a multi-fence approach that implements SAV at three levels of the
   network: access, intra-domain, and inter-domain.  As described in
   [RFC6620] and [RFC7039] the applicability of FCFS SAVI is limited to
   local traffic, to verify if the traffic generated by the hosts
   attached to the local link contains a valid source address.  The
   verification of the source address of the inter-subnet traffic is out
   of the scope of FCFS SAVI.  Other techniques are recommended to
   validate inter-subnet traffic.  The scope of the Source Address
   Validation in Intra-domain and Inter-domain Networks (SAVNET)
   includes the SAV function for both intra-domain and inter-domain

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   networks.  It identifies the technical gaps and fundamental problems
   with current mechanism and techniques, and specifies the practical
   requirements for the solution of these problems.  In that sense, FCFS
   SAVI complements SAVNET and the security level can be increased by
   combining these two techniques.

7.  Security Considerations

8.  IANA Considerations

   This specification does not require IANA action.

9.  Contributors

10.  Acknowledgments

11.  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>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/info/rfc4861>.

   [RFC5210]  Wu, J., Bi, J., Li, X., Ren, G., Xu, K., and M. Williams,
              "A Source Address Validation Architecture (SAVA) Testbed
              and Deployment Experience", RFC 5210,
              DOI 10.17487/RFC5210, June 2008,
              <https://www.rfc-editor.org/info/rfc5210>.

   [RFC5227]  Cheshire, S., "IPv4 Address Conflict Detection", RFC 5227,
              DOI 10.17487/RFC5227, July 2008,
              <https://www.rfc-editor.org/info/rfc5227>.

   [RFC6620]  Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS
              SAVI: First-Come, First-Served Source Address Validation
              Improvement for Locally Assigned IPv6 Addresses",
              RFC 6620, DOI 10.17487/RFC6620, May 2012,
              <https://www.rfc-editor.org/info/rfc6620>.

   [RFC6085]  Gundavelli, S., Townsley, M., Troan, O., and W. Dec,
              "Address Mapping of IPv6 Multicast Packets on Ethernet",
              RFC 6085, DOI 10.17487/RFC6085, January 2011,
              <https://www.rfc-editor.org/info/rfc6085>.

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   [RFC7039]  Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
              "Source Address Validation Improvement (SAVI) Framework",
              RFC 7039, DOI 10.17487/RFC7039, October 2013,
              <https://www.rfc-editor.org/info/rfc7039>.

   [RFC7513]  Bi, J., Wu, J., Yao, G., and F. Baker, "Source Address
              Validation Improvement (SAVI) Solution for DHCP",
              RFC 7513, DOI 10.17487/RFC7513, May 2015,
              <https://www.rfc-editor.org/info/rfc7513>.

   [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>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [RFC9161]  Rabadan, J., Ed., Sathappan, S., Nagaraj, K., Hankins, G.,
              and T. King, "Operational Aspects of Proxy ARP/ND in
              Ethernet Virtual Private Networks", RFC 9161,
              DOI 10.17487/RFC9161, January 2022,
              <https://www.rfc-editor.org/info/rfc9161>.

   [I-D.sajassi-bess-evpn-first-hop-security]
              Sajassi, A., Krattiger, L., Ananthamurthy, K., Rabadan,
              J., and W. Lin, "EVPN First Hop Security", Work in
              Progress, Internet-Draft, draft-sajassi-bess-evpn-first-
              hop-security-02, 22 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-sajassi-bess-
              evpn-first-hop-security-02>.

12.  Informative References

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <https://www.rfc-editor.org/info/rfc4862>.

Authors' Addresses

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   Eric Levy-Abegnoli
   Cisco Systems, Inc
   Emerald Square, Batiment C
   rue Evariste Galois
   06410 BIOT - Sophia Antipolis
   France
   Phone: +33 497 23 26 20
   Email: elevyabe@cisco.com

   Pascal Thubert
   Cisco Systems, Inc
   Emerald Square, Batiment C
   rue Evariste Galois
   06410 BIOT - Sophia Antipolis
   France
   Phone: +33 497 23 26 34
   Email: pthubert@cisco.com

   Ratko Kovacina
   Cisco Systems, Inc
   2000 Innovation Dr
   Kanata, ON K2K 3E8, Canada  ON K2K 3E8
   Canada
   Phone: +1 613 254 4545
   Email: rkovacin@cisco.com

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