A SAVI Solution for WLAN
draft-bi-savi-wlan-09

Network Working Group                                              J. Bi
Internet Draft                                                     J. Wu
Intended status: Standard Tracks                                 Y. Wang
Expires: August, 2016                                Tsinghua University
                                                                  T. Lin
                                            Hangzhou H3C Tech. Co., Ltd.
                                                        February 1, 2016

                         A SAVI Solution for WLAN
                         draft-bi-savi-wlan-09.txt

Abstract

   This document describes a source address validation solution for WLAN
   enabling 802.11i or other security mechanisms. This mechanism snoops
   NDP and DHCP packets to bind IP address to MAC address, and relies on
   the security of MAC address 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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 2, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ................................................ 2
   2. Conventions used in this document............................ 3
   3. IP-MAC Binding .............................................. 3
      3.1. Data Structures......................................... 3
         3.1.1. IP-MAC Mapping Table............................... 3
         3.1.2. MAC-IP Mapping Table............................... 4
      3.2. Pre-conditions for binding.............................. 4
      3.3. Binding IP addresses to MAC addresses................... 4
      3.4. Binding Migration....................................... 5
      3.5. Binding Clearing........................................ 5
   4. Source Address Validation.................................... 6
   5. Deployment Scenarios......................................... 6
      5.1. Centralized WLAN........................................ 6
         5.1.1. AP Filtering....................................... 7
            5.1.1.1. Candidate Binding............................. 7
            5.1.1.2. Packet Filtering.............................. 7
            5.1.1.3. CAPWAP Extension.............................. 7
            5.1.1.4. Mobility Solution............................. 9
         5.1.2. AC Filtering...................................... 10
      5.2. Autonomous WLAN........................................ 10
   6. Security Considerations..................................... 10
   7. IANA Considerations ........................................ 11
   8. Acknowledgments ............................................ 11
   9. References ................................................. 11
      9.1. Normative References................................... 11
      9.2. Informative References................................. 12

1. Introduction

   This document describes a mechanism to perform per packet IP source
   address validation in WLAN. This mechanism performs ND snooping or
   DHCP snooping to bind allocated IP address with authenticated MAC
   address. Static addresses are bound to the MAC addresses of
   corresponding hosts manually. Then the mechanism can check validity

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   of source IP address in local packets according to the binding
   association. The security of MAC address is assured by 802.11i or
   other mechanisms, thus the binding association is secure.

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

   There are three deployment scenarios specified in this document. The
   mechanism is deployed on different devices in different scenarios.
   The deployment detail is described in the document.

   When hosts move from one access point to another, the migration of
   binding entries may be triggered according to the specific mobility
   scenario. The mechanism to handle host mobility is specified in the
   document according to different deployment scenarios.

2. Conventions used in this document

   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 RFC-2119 [RFC2119].

3. IP-MAC Binding

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

3.1. Data Structures

3.1.1. IP-MAC Mapping Table

   This table maps IP addresses to corresponding MAC addresses. IP
   address is the index of the table. One IP address can only have one
   corresponding MAC address, while different IP addresses can be mapped
   to the same MAC address.

   This table is used in control process. Before creating new IP-MAC
   bindings, this table must first be consulted in case of conflict in
   binding entries. Also, this table must be consulted before doing any
   packet filtering. This table must be synchronized with the MAC-IP
   table specified in Section 3.1.2.

   Each entry in IP-MAC mapping table must also record the binding state
   of the IP address. Addresses snooped in DHCP address assignment
   procedure must record its state as "DHCPv6", and addresses snooped in

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   Duplicate Address Detection procedure must record its state as
   "SLAAC".

   Each entry in IP-MAC mapping table has its lifetime. According to
   [RFC3315], the address allocated by DHCP has a limited lifetime, so
   the related entry records its lifetime the same as that of the
   address. According to [RFC4862], stateless address also has a limited
   lifetime, and the host set this lifetime by itself. Thus the related
   entry also records its lifetime the same as that of the address.

3.1.2. MAC-IP Mapping Table

   This table maps MAC addresses to corresponding IP addresses. 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.
   Though multiple MAC addresses may exist on one interface, these MAC
   addresses must be mapped to different IP addresses.

   This table is used for filtering. Different from wired network, MAC-
   IP mapping table and IP-MAC mapping table can be maintained
   separately on different devices. Mechanisms for synchronization
   between the two tables must be employed for the consistency of the
   bindings. We will specify the details in Section 5 according to
   different deployment scenarios.

3.2. Pre-conditions for binding

   In the binding based mechanism, the security of IP address is based
   on the security of the binding anchor. In WLAN, a number of security
   mechanisms on link layer make MAC address a strong enough binding
   anchor, for instance, 802.11i, WAPI, WEP.

   If MAC address has no protection, attackers can spoof MAC address to
   succeed in validation. However, in general cases, if MAC address is
   not protected, more serious attack can be launched than IP spoofing
   attack.

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.

   An individual procedure handles binding DHCP addresses to MAC
   addresses. This procedure snoops the DHCP address assignment
   procedure between attached hosts and DHCP server. DHCP snooping in
   WLAN is the same as that in wired network specified in [RFC7513].

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   An individual procedure handles binding stateless addresses to MAC
   addresses. This procedure snoops Duplicate Address Detection
   procedure. ND snooping in WLAN is the same as that in wired network
   specified in [RFC6620].

   Data packets MAY also trigger the establishment of new IP-MAC binding
   entries. Data packet with non-bound source IP address with a limited
   rate is collected to handle DAD message loss in SLAAC procedure,
   which can be quite frequent in wireless network. The detail of the
   procedure is specified in Section 4. However, this mechanism will
   bring potential security risks (e.g. attacks that aimed at exhausting
   available IP addresses). Thus, it is optional whether to enable the
   mechanism, and if it is enabled, additional security mechanisms MUST
   also be employed to cope with the risks. Related security
   considerations are discussed in Section 6.

   In some deployment scenarios, the function of address snooping and
   IP-MAC table maintaining may also be separated onto different devices.
   Thus to prevent conflictions in binding entries, the device snoops
   addresses must have interactions with the device maintains the IP-MAC
   table. We will specify the details in Section 5.1.1.

3.4. Binding Migration

   Different from wired network, SAVI for WLAN must handle migration of
   binding entries when mobile hosts move from one access point to
   another. After movement, hosts will not perform another address
   allocation procedure to obtain new IP addresses, but continue to use
   the existing IP address. Thus binding entries in the foreign device
   that the mobile hosts access to cannot be established by snooping. A
   new mechanism is needed to correctly migrate the binding entry
   related to the IP address of the mobile host from the home device to
   the foreign device. We will specify the details in Section 5,
   according to different deployment scenarios.

3.5. Binding Clearing

   Three kinds of events will trigger binding clearing:

   1. The lifetime of an IP address in one entry has expired. This IP
   entry MUST be cleared.

   2. A host leaves this access point. The entries for all the related
   MAC addresses MUST be cleared.

   3. A DHCP RELEASE message is received from the owner of corresponding
   IP address. This IP entry MUST be cleared.

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4. Source Address Validation

   This section describes source address validation procedure on packet.
   In this procedure, all the frames are assumed to have passed the
   verifications of 802.11i or other security mechanisms.

   This procedure has the following steps:

   1. Extract the IP source and MAC source from the frame. Lookup the
   MAC address in the MAC-IP Mapping Table and check if the MAC-IP pair
   exists. If yes, forward the packet. Or else go to step 2.

   2. Lookup the IP address in the IP-MAC Mapping Table and check if the
   IP address exists. If no, go to step 3. If yes, check whether The MAC
   address in the entry is the same as that in the frame. If yes,
   forward the packet. Else drop the packet.

   3. If the mechanism that allows data packets to trigger the
   establishment of new IP-MAC binding entries is enabled, insert a new
   entry into the IP-MAC Mapping Table and forward the packet. Otherwise
   drop the packet.

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

   Also in step 3, if a new IP-MAC binding entry is established, it
   should be synchronized to MAC-IP mapping table.

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 respectively in each scenario.

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.

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5.1.1. AP Filtering

   In this scenario, AC maintains IP-MAC Mapping Table while AP
   maintains MAC-IP Mapping Table and perform address snooping.

5.1.1.1. Candidate Binding

   AP executes the procedure specified in Section 3.3. Candidate binding
   is generated after snooping procedure. Candidate binding must be
   confirmed by AC to be valid.

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

5.1.1.2. Packet Filtering

   As specified in Section 4, for incoming data packets, AP looks up the
   MAC address in the local MAC-IP Mapping Table and check if the MAC-IP
   pair exists. If yes, AP forwards the packet. Or else AP delivers the
   packet to AC for further processing.

   When receiving data packets from AP, AC Looks up the IP address in
   the local IP-MAC Mapping Table and checks if the IP address exists.
   If no, according to whether the AC is configured to allow data
   packets to trigger binding entry creations, AC establishes a new IP-
   MAC entry then forwards the packet, or drop the packet. If yes, AC
   checks whether The MAC address in the entry is the same as that in
   the frame. If yes, AC forwards the packet. Else AC drops the packet.

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

5.1.1.3. CAPWAP Extension

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

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   The host IP message element can be used in the process of
   confirmation of candidate binding. When AP generates a candidate
   binding, it reports the MAC address and related IP addresses to AC
   using this message, with suggestions of the state and lifetime of
   each IP address as specified in Section 3.1.1. After AC checks the
   validation of the candidate binding, it replies using a message of
   the same format to inform AP the validation of each IP address with
   suggestions of its state and lifetime.

   The host IP message element also can be used in the process of
   binding migration. In mobility scenario, foreign device the mobile
   hosts accesses to need to request related bindings from home devices,
   and host IP message element can be used for interactions between them.
   Details will be specified in the following sections according to
   different deployment scenarios.

        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    |        IPv4 Address...        +
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    IPv4 Address...                            +
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    IPv6 flag  |     Length    |        IPv6 Address...        +
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    IPv6 Address...                            +
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   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.

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   Length: The length of the Value field.

   Description: A 16-bit value for descriptions 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] are supported.

   MAC Address: A MAC address of the host.

   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 state (only value 1 is used for now), and a 32-bit
   value for lifetime.

   IPv6 flag: An 8-bit value representing that the sub-field's type is
   IPv6 address, whose value is 3.

   Length: The length of the IPv6 Address field.

   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 state (also one value for now), and a 32-bit value
   lifetime.

5.1.1.4. Mobility Solution

   When a host moves from one AP to another, layer-2 association happens
   before IP packet transfer. Home AP deletes the binding when mobile
   host is disconnected, and foreign AP immediately requests the bound
   addresses with the associated MAC from AC using host IP message
   element specified in Section 5.1.1.2. AC returns the binding with
   suggestions of its state and lifetime also using the new CAPWAP
   protocol message. After AP get the addresses should be bound, the
   binding migration is completed.

   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. CAPWAP extensions

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   specified in Section 5.1.1.2 can also be used for communications
   between AC.

5.1.2. AC Filtering

   In this scenario, AC maintains both MAC-IP and IP-MAC Mapping Table
   and performs both address snooping and packet filtering. So all the
   packets must be forwarded to AC firstly.

   AC executes the procedure specified in Section 3.3 and check 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.

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

   Mobility within one AC does not trigger any binding migration.
   Mobility between different ACs triggers binding migration. ACs must
   communicate to perform the binding migration. CAPWAP extensions
   specified in Section 5.1.1.2 can be used for communications between
   ACs.

5.2. Autonomous WLAN

   Autonomous WLAN is comprised of FAT Access Points. In this scenario,
   FAT AP maintains both MAC-IP and IP-MAC Mapping Table and performs
   both address snooping and packet filtering.

   FAT AP executes the procedure specified in Section 3.3 and check 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.

   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. CAPWAP
   extensions specified in Section 5.1.1.2 can be used for
   communications between FAT AP.

6. 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 firstly.

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   In Section 3.3, a mechanism is described to allow data packets to
   trigger the establishment of new binding entries. If the mechanism is
   enabled, it can be used to launch attacks which may finally leads to
   exhaustion of available IP addresses. If no restriction is taken, the
   attacker can make as many IP-MAC bindings as possible with the same
   MAC address. In this way, other hosts may fail to trigger any binding
   entry establishment and thus cannot get their packets pass the SAVI
   device. To cope with the potential security risks, additional
   mechanism MUST be employed, e.g. to limit the maximum number of IP
   addresses that one MAC address can bind to.

7. IANA Considerations

   There is no IANA Consideration currently.

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, March 1997.

   [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and
             M. Carney, "Dynamic Host Configuration Protocol for IPv6
             (DHCPv6)", RFC3315, July, 2003.

   [RFC4862] Thomson, S., Narten, T. and T. Jinmei, "IPv6 Stateless
             Autoconfiguration", RFC4862, September, 2007.

   [RFC6620] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, " FCFS
             SAVI: First-Come, First-Served Source Address Validation
             Improvement for Locally Assigned IPv6 Addresses", RFC6620,
             May, 2012.

   [RFC5415] Calhoun, P., Montemurro, M., and D. Stanley, "Control And
             Provisioning of Wireless Access Points (CAPWAP) Protocol
             Specification", RFC5415, March, 2009.

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   [RFC7513] Bi, J., Wu, J., Yao, G., and F. Baker, "Source Address 
             Validation Improvement (SAVI) Solution for DHCP", 
             RFC7513, May 2015.

9.2. Informative References

   [EUI-48]  "Guidelines For 48-bit Global Identifier (EUI-48)",
             http://standards.ieee.org/develop/regauth/tut/eui48.pdf

   [EUI-64]  "Guidelines For 64-bit Global Identifier (EUI-64)",
             http://standards.ieee.org/develop/regauth/tut/eui64.pdf

Authors' Addresses

   Jun Bi
   Tsinghua University
   Network Research Center, Tsinghua University
   Beijing  100084
   China
   EMail: junbi@cernet.edu.cn

   Jianping Wu
   Tsinghua University
   Computer Science, Tsinghua University
   Beijing  100084
   China
   EMail: jianping@cernet.edu.cn

   You Wang
   Tsinghua University
   Network Research Center, Tsinghua University
   Beijing  100084
   China
   EMail: wangyou10@mails.tsinghua.edu.cn

   Tao Lin
   Hangzhou H3C Tech. Co., Ltd.
   Beijing 100085
   China
   EMail: lintao@h3c.com

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