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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://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 April 4, 2012. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. Bi, et al. Expires Apr 4, 2012 [Page 1] Internet-Draft SAVI wlan October 2011 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 to this document. Code Components extracted from this document must 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. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. 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 Bi, et al. Expires Apr 4, 2012 [Page 2] Internet-Draft SAVI wlan October 2011 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. Bi, et al. Expires Apr 4, 2012 [Page 3] Internet-Draft SAVI wlan October 2011 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. Bi, et al. Expires Apr 4, 2012 [Page 4] Internet-Draft SAVI wlan October 2011 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. Bi, et al. Expires Apr 4, 2012 [Page 5] Internet-Draft SAVI wlan October 2011 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. Bi, et al. Expires Apr 4, 2012 [Page 6] Internet-Draft SAVI wlan October 2011 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. Bi, et al. Expires Apr 4, 2012 [Page 7] Internet-Draft SAVI wlan October 2011 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. Bi, et al. Expires Apr 4, 2012 [Page 8] Internet-Draft SAVI wlan October 2011 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. Bi, et al. Expires Apr 4, 2012 [Page 9] Internet-Draft SAVI wlan October 2011 [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 Bi, et al. Expires Apr 4, 2012 [Page 10] Internet-Draft SAVI wlan October 2011 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 Bi, et al. Expires Apr 4, 2012 [Page 11]