Source Address Validation Improvements (SAVI)                    J.B. Bi
Internet-Draft                                                   J.W. Wu
Intended status: Standards Track                     Tsinghua University
Expires: 12 November 2022                                       T.L. Lin
                                            New H3C Technologies Co. Ltd
                                                               Y.W. Wang
                                                                 L.H. He
                                                     Tsinghua University
                                                             11 May 2022


                        A SAVI Solution for WLAN
                         draft-bi-savi-wlan-23

Abstract

   This document describes a source address validation solution for
   WLANs where 802.11i or other security mechanisms are enabled to
   secure MAC addresses.  This mechanism snoops NDP and DHCP packets to
   bind IP addresses to MAC addresses, and relies on the security of MAC
   addresses guaranteed by 802.11i or other mechanisms to filter IP
   spoofing packets.  It can work in the special situations described in
   the charter of SAVI (Source Address Validation Improvements)
   workgroup, such as multiple MAC addresses on one interface.  This
   document describes three different deployment scenarios, with
   solutions for migration of binding entries when hosts move from one
   access point to another.

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 12 November 2022.







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Copyright Notice

   Copyright (c) 2022 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  IP-MAC Binding  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Data Structures . . . . . . . . . . . . . . . . . . . . .   4
       3.1.1.  IP-MAC Mapping Table  . . . . . . . . . . . . . . . .   4
       3.1.2.  MAC-IP Mapping Table  . . . . . . . . . . . . . . . .   4
     3.2.  Pre-conditions for Binding  . . . . . . . . . . . . . . .   5
     3.3.  Binding IP addresses to MAC addresses . . . . . . . . . .   5
     3.4.  Binding Migration . . . . . . . . . . . . . . . . . . . .   6
     3.5.  Binding Clearing  . . . . . . . . . . . . . . . . . . . .   6
   4.  Source Address Validation . . . . . . . . . . . . . . . . . .   6
   5.  Deployment Scenarios  . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Centralized WLAN  . . . . . . . . . . . . . . . . . . . .   7
       5.1.1.  AP Filtering  . . . . . . . . . . . . . . . . . . . .   7
         5.1.1.1.  Candidate Binding . . . . . . . . . . . . . . . .   7
         5.1.1.2.  Packet Filtering  . . . . . . . . . . . . . . . .   8
         5.1.1.3.  Negative Entries  . . . . . . . . . . . . . . . .   8
         5.1.1.4.  CAPWAP Extension  . . . . . . . . . . . . . . . .   9
         5.1.1.5.  Mobility Solution . . . . . . . . . . . . . . . .  12
       5.1.2.  AC Filtering  . . . . . . . . . . . . . . . . . . . .  12
     5.2.  Autonomous WLAN . . . . . . . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
     7.1.  Privacy Considerations  . . . . . . . . . . . . . . . . .  14
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15





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1.  Introduction

   This document describes a mechanism for performing per-packet IP
   source address validation in wireless local area networks (WLANs).
   The mechanism performs ND snooping or DHCP snooping to bind the
   assigned IP address to the verified MAC address.  Static addresses
   are manually bound to the MAC address of the corresponding host.  The
   mechanism can then check the validity of the source IP address in the
   local packet against the binding association.  The MAC address is
   secured by 802.11i or other mechanisms, so the binding association is
   secure.

   This mechanism utilizes two important data structures, the IP-MAC
   mapping table on the control plane and the MAC-IP mapping table on
   the data plane, to implement source address validation, which is
   described in detail in this document.

   The case of an interface with multiple MAC addresses is a special
   case mentioned in the SAVI charter and is the only special case that
   challenges MAC-IP binding.  The mechanism to handle this case is
   specified in the document.

   Three deployment scenarios for this mechanism are specified in this
   document, describing the devices and details of deployment in
   different scenarios.

   When a host moves from one access point to another, the migration of
   binding entries can be triggered depending on the specific mobility
   scenario.  The mechanism for handling host mobility is specified in
   the documentation based on different deployment scenarios.

1.1.  Terminology

   FIT access points: The access points used in centralized WLAN
   deployment scenario.

   FAT access points: The access points used in autonomous WLAN
   deployment scenario.

   Binding anchor: A "binding anchor" is defined to be a physical and/or
   link-layer property of an attached device, as defined in [RFC7039].
   In this document, the binding anchor refers to th MAC address.

   Binding entry: A rule that associates an IP address with a binding
   anchor.

   Familiarity with SAVI-DHCP and its terminology, as defined in
   [RFC7513], is assumed.



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2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  IP-MAC Binding

   This section specifies the operations for creating and clearing
   bindings between IP addresses and MAC addresses.

3.1.  Data Structures

   The binding relationship between IP address and MAC address is stored
   using two data structures, i.e., the IP-MAC mapping table and MAC-IP
   mapping table.

3.1.1.  IP-MAC Mapping Table

   This table maps IP addresses to their corresponding MAC addresses.
   The IP address is the index of the table.  An IP address can have
   only one corresponding MAC address.  Different IP addresses can be
   mapped to the same MAC address.

   This table is used in the control process.  Before creating a new IP-
   MAC binding, this table must be queried to prevent conflicting
   binding entries.  Also, this table must be queried before any packet
   filtering is performed.  This table must be synchronized with the
   MAC-IP mapping table specified in Section 3.1.2.

   Each entry in the IP-MAC mapping table must also record the binding
   method of the IP address.  Addresses snooped in the DHCP address
   assignment procedure must have their binding method recorded as
   "DHCP", and addresses snooped in the Duplicate Address Detection
   procedure [RFC4862] must have their binding method recorded as
   "SLAAC".

3.1.2.  MAC-IP Mapping Table

   This table maps MAC addresses to the corresponding IP addresses.  The
   MAC address is the index of the table.  It is a one-to-many mapping
   table, which means a MAC address can be mapped to multiple IP
   addresses.  Although multiple MAC addresses may exist on one
   interface, these MAC addresses must be mapped to different IP
   addresses.






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   This table is used for filtering.  Different from wired networks, the
   MAC-IP mapping table and the IP-MAC mapping table can be maintained
   separately on different devices.  A synchronization mechanism must be
   used between these two tables to ensure the consistency of the
   bindings.  We will explain the details in Section 5 for different
   deployment scenarios.

3.2.  Pre-conditions for Binding

   As specified in [RFC7039], in a binding-based mechanism, the security
   of IP address is dependent on the security of the binding anchor.  In
   WLANs, 802.11i or other link-layer security mechanisms make MAC
   address a strong enough binding anchor.

   If the MAC address is unprotected, an attacker can spoof the MAC
   address to pass validation successfully.

3.3.  Binding IP addresses to MAC addresses

   All the static IP-MAC address pairs are configured into the IP-MAC
   mapping table with the mechanism enabled.

   A separate procedure handles the binding of DHCP addresses to MAC
   addresses.  This procedure snoops on the DHCP address assignment
   process between the attached host and the DHCP server.  DHCP snooping
   in WLANs is the same as that in wired networks specified in
   [RFC7513].

   A separate procedure handles the binding of stateless addresses to
   MAC addresses.  This procedure snoops Duplicate Address Detection
   procedure as described in [RFC4862] or Address Resolution procedure
   between attached hosts and neighbors as described in [RFC4861].
   Based on the principle of roaming experience first in WLAN, the new
   binding anchor is selected in preference and triggers the deletion of
   the secure connection of the old binding anchor.

   In some deployment scenarios, the functions of address snooping and
   IP-MAC mapping table maintenance may also be separated to different
   devices.  Therefore, to prevent conflicting binding entries, the
   device for address snooping must interact with the device that
   maintains the IP-MAC mapping table.  We will specify the details in
   Section 5.1.1.









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3.4.  Binding Migration

   Different from wired networks, SAVI for WLAN must handle the
   migration of binding entries when a mobile host moves from one access
   point to another.  After the move, the host will not perform another
   address configuration procedure to obtain new IP addresses but
   continue to use the existing IP address(es).  Thus, binding entries
   in the foreign device accessed by mobile hosts cannot be established
   by snooping.  A new mechanism is needed to correctly migrate the
   binding entry associated with the mobile host's IP address from the
   home device to the foreign device.  If the host binds multiple
   entries, multiple entries will be migrated.  For example, when the
   host is assigned multiple addresses, multiple binding entries will be
   generated, and these entries will be migrated.  We will specify the
   details in Section 5 depending on different deployment scenarios.

3.5.  Binding Clearing

   Three kinds of events will trigger binding clearing:

   1.  A host leaves explicitly this access point.  All entries in the
      MAC-IP mapping table associated with this MAC address MUST be
      cleared.

   2.  A DHCP RELEASE message is received from the owner of the
      corresponding IP address.  This IP entry in the IP-MAC mapping
      table and the corresponding entries in the MAC-IP mapping table
      MUST be cleared.

   3.  A timeout message of the AC's client idle-time is received.  All
      entries in the MAC-IP mapping table related to the MAC address
      MUST be cleared.

4.  Source Address Validation

   This section describes source address validation procedure for
   packets.  In this procedure, all the frames are considered to have
   passed the verification of 802.11i or other security mechanisms.

   This procedure has the following steps:

   1.  Extract the IP source address and MAC source address from the
      frame.  Look up the MAC address in the MAC-IP mapping table and
      check if the MAC-IP pair exists.  If exists, forward the packet.
      Otherwise, go to step 2.

   2.  Look up the IP address in the IP-MAC mapping table and check if




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      the IP address exists.  If it does not exist, go to step 3.  If it
      exists, check whether the MAC address in the entry is the same as
      that in the frame.  If so, forward the packet.  Otherwise, drop
      the packet.

   In step 2, after the packet is judged to be valid and forwarded,
   synchronization between the MAC-IP and IP-MAC mapping tables should
   be triggered.  The MAC-IP binding of the packet should be
   synchronized from the IP-MAC mapping table to the MAC-IP mapping
   table, and thus subsequent packets with the same MAC-IP pair will be
   forwarded without going to step 2.

5.  Deployment Scenarios

   This section specifies three deployment scenarios, including two
   under centralized WLAN and one under autonomous WLAN.  The deployment
   details and solutions for host mobility between access points are
   described for each scenario, respectively.

5.1.  Centralized WLAN

   Centralized WLAN is comprised of FIT access points (AP) and access
   controllers (AC).  In this scenario, this document proposes the
   following two deployment solutions.

5.1.1.  AP Filtering

   With this deployment scheme, validated data packets received by an AP
   do not pass through the AC; only control packets and the questionable
   data packets pass through the AC.  In this case, the AC maintains the
   IP-MAC mapping table, while the AP maintains the MAC-IP mapping table
   and performs address snooping.

5.1.1.1.  Candidate Binding

   An AP executes the procedure specified in Section 3.3.  The candidate
   bindings are generated after the snooping procedure.  Candidate
   bindings MUST be confirmed by the AC to be valid.

   After a candidate binding is generated, the AC is notified and checks
   whether the binding is valid or not.  If a candidate binding does not
   violate any existing binding in the IP-MAC mapping table, the
   validity of the binding is determined.  Otherwise, if an address is
   not suitable for use by the host, the AC notifies the corresponding
   AP.  If the candidate binding is valid, the AC adds an entry to the
   IP-MAC mapping table and notifies the AP.  Afterwards, the AP also
   adds an entry to the local MAC-IP mapping table.




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5.1.1.2.  Packet Filtering

   As specified in Section 4, for incoming data packets, an AP looks up
   the MAC address in the local MAC-IP mapping table and checks if the
   MAC-IP pair exists.  If exists, the AP forwards the packet.
   Otherwise, the AP delivers the packet to the AC for further
   processing.

   When receiving a data packet from the AP, the AC looks up the IP
   address in the local IP-MAC mapping table and checks if the IP
   address exists.  If it does not exist, the AC drops the packet.  If
   it exists, the AC checks whether the MAC address in the entry is the
   same as that in the frame.  If so, the AC forwards the packet.
   Otherwise, the AC drops the packet.

   After the AC forwards a valid packet, it synchronizes the associated
   MAC-IP binding to the MAC-IP mapping table on the AP from which the
   packet comes.  Subsequent packets with the same MAC-IP pair will be
   forwarded directly by the AP without going through the AC.

5.1.1.3.  Negative Entries

   In the AP filtering scenario, APs MAY drop packets directly without
   sending them to the AC by enabling the establishment of negative
   entries on APs.  Specifically, APs may establish negative entries in
   the following circumstances.

   1.  When an AP receives a certain number of packets within a certain
      amount of time with the same MAC-IP pair that does not exist in
      the local MAC-IP mapping table, it establishes a negative entry
      for this MAC-IP pair.  Then the AP drops all following packets
      that have the same MAC-IP pair as indicated in this negative entry
      without sending them to the AC for further processing.

   2.  When an AP receives a certain number of packets within a certain
      amount of time with the same MAC address but different MAC-IP
      pairs and none of these MAC-IP pairs exist in the local MAC-IP
      mapping table, it establishes a negative entry for this MAC
      address.  Then the AP drops all the following packets that have
      the same MAC address as indicated in this negative entry without
      sending them to the AC for further processing.

   Each negative entry has a limited lifetime.  The number of packets
   and duration of time to trigger the establishment of the negative
   entry, and the lifetime of the negative entry are configurable.






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5.1.1.4.  CAPWAP Extension

   CAPWAP protocol is used for communication between the AP and the AC.
   A new CAPWAP protocol message element is introduced, which extends
   [RFC5415].  The host IP message element is used by both the AP and
   the AC to exchange the binding information of hosts.

   The host IP message element can be used in the process of confirming
   candidate bindings.  When the AP generates a candidate binding, it
   reports the MAC address and related IP addresses to the AC using this
   message, with suggestions of the status of each IP address (e.g.,
   available, unavailable, candidate).  After the AC checks the validity
   of the candidate binding, it replies using a message of the same
   format, informing the AP of the validation of each IP address with a
   suggested status.

   The host IP message element can be used in the process of binding
   migration.  When migration occurs, the source device uses this
   message to report the MAC address and related IP addresses to the
   destination device, with suggestions for the status of each IP
   address.  After the destination device checks the validity of the
   candidate binding, it replies using a message of the same format to
   inform the source device of the validity of each IP address with a
   suggested status.

   The host IP message element can also be used in other scenarios when
   the synchronization between MAC-IP and IP-MAC mapping tables is
   required as specified in Section 3.5 and Section 4.  When the
   synchronization from IP-MAC mapping table to MAC-IP mapping table is
   triggered, the source device which holds the IP-MAC mapping table
   reports the MAC address and the related IP addresses to the
   destination device which holds the MAC-IP mapping table using this
   message, with suggestions of the status of each IP address.  The
   destination device replies using a message of the same format to
   acknowledge the source device.

     0               1               2               3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Radio ID   |                 Total Length                  +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Sender ID   |     Length    |         Description           +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    MAC flag   |     Length    |        MAC Address...         +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     MAC Address...                            +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    IPv4 flag  |     Length    |        blank       ...        +



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     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    IPv4 Address 1(32 bit)                     +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Status     |        blank       ...                        +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    lifetime                                   +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    IPv4 Address 2(32 bit)                     +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Status     |        blank       ...                        +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    lifetime                                   +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    ........                                   +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    IPv4 Address n(32 bit)                     +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Status     |        blank       ...                        +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    lifetime                                   +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    IPv6 flag  |     Length    |        IPv6 Address...        +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    IPv6 Address 1(128 bit)                    +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Status     |        blank       ...                        +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    lifetime                                   +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    IPv6 Address 2(128 bit)                    +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Status     |        blank       ...                        +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    lifetime                                   +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    ........                                   +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    IPv6 Address n(128 bit)                    +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Status     |        blank       ...                        +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    lifetime                                   +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   BSSID flag  |     Length    |        BSSID...               +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     BSSID                                     +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   Radio ID: An 8-bit value representing the radio, whose value is
   between 1 and 31.

   Total Length: Total length of the following fields.

   Sender ID: An 8-bit value representing the sender of the message.  AP
   is represented by value 1 and AC is represented by value 2.

   Length: The length of the Value field.

   Description: A 16-bit value for a description of the sender (AP or
   AC).

   MAC flag: An 8-bit value representing that the sub-field's type is
   MAC address, whose value is 1.

   Length: The length of the MAC Address field.  The formats and lengths
   specified in EUI-48 and EUI-64 [EUI] are supported.

   MAC Address: A MAC address of the host.  At least one MAC address
   block MUST appear in the message, otherwise the message is considered
   as invalid.

   IPv4 flag: An 8-bit value representing that the sub-field's type is
   IPv4 address, whose value is 2.

   Length: The length of the IPv4 Address field.

   IPv4 Address: An IPv4 address of the host.  There may exist many
   entries, and each entry is comprised of an IPv4 address, an 8-bit
   value for address status (value 1 means available, value 0 means
   unavailable, value 255 means candidate), and a 32-bit value for
   lifetime.  Lifetime is a reserved field for future application under
   abnormal conditions.  It is required to list all IPv4 addresses
   before IPv6 address blocks.

   IPv6 flag: An 8-bit value representing that the sub-field's type is
   IPv6 address, a DHCPv6-assigned IP address represented by value 3 and
   a locally assigned IP address represented by value 4.

   Length: The length of the IPv6 Address field.










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   IPv6 Address: An IPv6 address of the host.  There may exist many
   entries, and each entry is comprised of an IPv6 address, an 8-bit
   value of address status (value 1 means available, value 0 means
   unavailable, value 255 means candidate), and a 32-bit value lifetime.
   Lifetime is a reserved field for future application under abnormal
   conditions.  All IPv4 and IPv6 addresses bind to the MAC address that
   appears before them in the message.

   BSSID flag: An 8-bit value representing that the sub-field's type is
   BSSID, whose value is 5.

   Length: The length of the BSSID field.  The formats and lengths
   specified in EUI-48 and EUI-64 [EUI] are supported.

   BSSID: A basic service set identifier representing the BSS.

5.1.1.5.  Mobility Solution

   When a host moves from one AP to another, layer-2 association happens
   before the IP packets are forwarded.  The home AP deletes the binding
   when the mobile host is disconnected, and the foreign AP immediately
   requests the bound addresses with the associated MAC address from the
   AC.  The AC returns the binding with a suggested status.  After the
   foreign AP gets the addresses that should be bound, the binding
   migration is completed.  The protocol used for communication between
   the foreign AP and the AC is the same as described in
   Section 5.1.1.4, while in this scenario, the AC serves the role of
   the source device and the foreign AP serves the role of the
   destination device.

   In WLAN, a host can move from an AC to another AC while keeping using
   the same IP address.  To be compatible with such scenario, ACs must
   communicate to perform the binding migration.  The protocol used for
   communication between ACs is the same as described in
   Section 5.1.1.4, while in this scenario the home AC serves the role
   of the source device and the foreign AC serves the role of the
   destination device.

5.1.2.  AC Filtering

   In this scenario, an AC maintains both the MAC-IP and IP-MAC mapping
   tables and performs both address snooping and packet filtering.
   Therefore, all the packets must be forwarded to the AC first.

   The AC executes the procedure specified in Section 3.3 and checks the
   validity of IP-MAC pairs by consulting the local IP-MAC mapping
   table.  No extra procedure is needed to establish the IP-MAC
   bindings.



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   The AC executes the procedure specified in Section 4 for packet
   filtering, and no extra procedure is involved.

   Host movement within an AC does not trigger any binding migration.
   Host movement between different ACs triggers binding migration.  ACs
   must communicate to perform binding migration.  The protocol used for
   communication between ACs is the same as described in
   Section 5.1.1.4, while in this scenario the home AC serves the role
   of the source device and the foreign AC serves the role of the
   destination device.

5.2.  Autonomous WLAN

   Autonomous WLAN is comprised of FAT access points.  In this scenario,
   a FAT AP maintains both the MAC-IP and IP-MAC mapping tables and
   performs both address snooping and packet filtering.

   The FAT AP executes the procedure specified in Section 3.3 and checks
   the validity of IP-MAC pairs by consulting the local IP-MAC mapping
   table.  No extra procedure is needed to establish the IP-MAC
   bindings.

   The FAT AP executes the procedure specified in Section 4 for packet
   filtering, and no extra procedure is involved.

   Mobility between different FAT APs will trigger binding migration.
   FAT APs must communicate to perform the binding migration.  The
   protocol used for communication between FAT APs is the same as
   described in Section 5.1.1.4, while in this scenario the home FAT AP
   serves the role of the source device and the foreign FAT AP serves
   the role of the destination device.

6.  IANA Considerations

   There is no IANA consideration currently.

7.  Security Considerations

   The security of address allocation methods matters the security of
   this mechanism.  Thus, it is necessary to improve the security of
   stateless auto-configuration and DHCP first.










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7.1.  Privacy Considerations

   A SAVI device MUST delete binding anchor information as soon as
   possible, except where there is an identified reason why that
   information is likely to be involved in the detection, prevention, or
   tracing of actual source-address spoofing.  Information about hosts
   that never spoof (probably the majority of hosts) SHOULD NOT be
   logged.

8.  Acknowledgements

   The authors would like to thank Guang Yao, Yang Shi, and Hao Wang for
   their contributions to this document.

9.  References

9.1.  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>.

9.2.  Informative References

   [EUI]      IEEE Standards Association, "Guidelines for Use of
              Extended Unique Identifier (EUI), Organizationally Unique
              Identifier (OUI), and Company ID (CID)", 2017,
              <https://standards.ieee.org/content/dam/ieee-
              standards/standards/web/documents/tutorials/eui.pdf>.

   [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>.

   [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>.

   [RFC5415]  Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
              Ed., "Control And Provisioning of Wireless Access Points
              (CAPWAP) Protocol Specification", RFC 5415,
              DOI 10.17487/RFC5415, March 2009,
              <https://www.rfc-editor.org/info/rfc5415>.





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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>.

Authors' Addresses

   Jun Bi
   Tsinghua University
   Beijing
   100084
   China
   Email: junbi@cernet.edu.cn


   Jianping Wu
   Tsinghua University
   Beijing
   100084
   China
   Email: jianping@cernet.edu.cn


   Tao Lin
   New H3C Technologies Co. Ltd
   466 Changhe Road, Binjiang District
   Hangzhou
   Zhejiang, 310052
   China
   Email: lintao@h3c.com


   You Wang
   Tsinghua University
   Beijing
   100084
   China
   Email: you@opennetworking.org








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   Lin He
   Tsinghua University
   Beijing
   100084
   China
   Email: he-l14@mails.tsinghua.edu.cn













































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