A SAVI solution for WLAN
draft-bi-savi-wlan-01

Network Working Group                                            J. Bi 
Internet Draft                                                   J. Wu 
Intended status: Standard Tracks                               Y. Wang 
Expires: APR, 2012                                 Tsinghua University 
                                                                T. Lin 
                                          Hangzhou H3C Tech. Co., Ltd. 
                                                       October 4, 2011 
                                   
 
                         A SAVI solution for WLAN 

                         draft-bi-savi-wlan-01.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 to bind IP address with 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 workgroup, such as multiple MAC 
   addresses on one interface. This document describes three different 
   deployment scenarios, with solutions for migration of mapping 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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   Internet-Drafts are draft documents valid for a maximum of six months 
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   This Internet-Draft will expire on April 4, 2012. 

Copyright Notice 

   Copyright (c) 2011 IETF Trust and the persons identified as the 
   document authors.  All rights reserved. 

 
 
 
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Table of Contents 

    
   1. Introduction ................................................ 3 
   2. Conventions used in this document............................ 3 
   3. IP-MAC Binding .............................................. 3 
      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.............................. 4 
      3.3. Binding IP addresses to MAC addresses................... 4 
      3.4. Clear Binding .......................................... 5 
   4. Source Address Validation.................................... 5 
   5. Deployment Scenarios......................................... 5 
      5.1. Centralized WLAN........................................ 6 
         5.1.1. AP Filtering....................................... 6 
            5.1.1.1. Candidate Binding............................. 6 
            5.1.1.2. CAPWAP Extension.............................. 6 
            5.1.1.3. Mobility Solution............................. 8 
         5.1.2. AC Filtering....................................... 8 
      5.2. Autonomous WLAN......................................... 8 
   6. Security Considerations...................................... 9 
   7. IANA Considerations ......................................... 9 
   8. Conclusions ................................................. 9 
 
 
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   9. Contributors ................................................ 9 
   10. Acknowledgments ............................................ 9 
   11. References ................................................. 9 
      11.1. Normative References
................................... 9 
      11.2. Informative References................................ 11 
    
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 stations manually. Then the mechanism can check 
   validity 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 
   mapping 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 of binding IP addresses to MAC 
   addresses, and the clear of binding.  

 
 
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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. This table must be synchronized with the MAC-IP 
   table specified in Section 3.1.2. 

   The address allocated by DHCP has a limited lifetime, so the related 
   entry has a limited lifetime, too. According to [RFC4862], stateless 
   address also has a limited lifetime, the stations set this lifetime 
   by itself.  

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 and we will specify the details in 
   Section 4. This table must be synchronized with the IP-MAC table 
   specified in Section 3.1.1. 

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.   
 
 
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   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 wired network. 

   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 wired network. 

3.4. Clear Binding 

   Three kinds of events will trigger clearing binding:  

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

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

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

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 next step.  

   2. Lookup the IP address in the IP-MAC Mapping Table and check if the 
   IP address exists. If no, insert a new entry into the IP-MAC Mapping 
   Table and forward the packet. 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.  

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. 

 
 
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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 

   In this scenario, AC maintains IP-MAC Mapping Table while AP 
   maintains MAC-IP Mapping Table. Packet filtering will be performed on 
   each AP as specified in Section 4. 

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. CAPWAP Extension 

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

   The host IP message element MAY be sent by AP. 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.  

   The host IP message element MAY be sent by AC. After AC checks the 
   validation of a 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. 

    

 
 
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        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                              + 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       |    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. 

   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. 
 
 
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   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. 

5.1.1.3. 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. After AC tells AP 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 specified in Section 5.1.1.2 can also be used for 
   communications between AC. The procedure of binding migration is the 
   similar to that in the previous scenario. Home AC deletes the binding 
   when mobile host is disconnected, and foreign AC requests the bound 
   addresses with the associated MAC from Home AC. 

5.1.2. AC Filtering 

   In this scenario, AC maintains both MAC-IP and IP-MAC Mapping Table 
   and performs packet filtering. So all the packets must be firstly be 
   forwarded to AC. AC executes the procedure specified in Section 3.3. 

   Mobility in one AC does not trigger any binding migration. Mobility 
   between different ACs triggers binding migration and the procedure is 
   the same as that in Section 5.1.1.3. 

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 
   packet filtering and executes the procedure specified in Section 3.3.

   Mobility between different FAT APs will trigger binding migration, 
   and the procedure is the same as that in Section 5.1.1.3. 

 
 
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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.  

7. IANA Considerations 

   There is no IANA Consideration currently.  

8. Conclusions 

   This solution can satisfy the requirements of SAVI charter in WLAN 
   enabling 802.11i or other security mechanisms. 

9. Contributors 

   Guang Yao 
   Tsinghua University 
   Network Research Center, Tsinghua University 
   Beijing  100084 
   China 
   EMail: yaog@netarchlab.tsinghua.edu.cn 
    
   Yang Shi 
   Hangzhou H3C Tech. Co., Ltd. 
   Beijing 100085 
   China 
   EMail: rishyang@gmail.com  
    
   Hao Wang 
   Hangzhou H3C Tech. Co., Ltd. 
   Beijing 100085 
   China 
   EMail: hwang@h3c.com 
 

10. Acknowledgments 

   This document was prepared using 2-Word-v2.0.template.dot.  

11. References 

11.1. Normative References 

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement 
         Levels", BCP 14, RFC 2119, March 1997. 
 
 
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   [2]  Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax 
         Specifications: ABNF", RFC 2234, Internet Mail Consortium and 
         Demon Internet Ltd., November 1997.  

   [3]  IEEE 802.11i-2004: Amendment 6: Medium Access Control (MAC) 
         Security Enhancements  

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate 
   Requirement Levels", BCP 14, RFC 2119, March 1997.  

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

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

   [RFC5415] Control And Provisioning of Wireless Access Points (CAPWAP) 
   Protocol Specification 

 
 
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11.2. Informative References 

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: wangyou@netarchlab.tsinghua.edu.cn 
    
   Tao Lin 
   Hangzhou H3C Tech. Co., Ltd. 
   Beijing 100085 
   China 
   EMail: lintaog@gmail.com 
    

 
 
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