Network Working Group J. Bi
Internet Draft J. Wu
Intended status: Standard Tracks Y. Wang
Expires: OCT, 2012 Tsinghua University
T. Lin
Hangzhou H3C Tech. Co., Ltd.
April 5, 2012
A SAVI solution for WLAN
draft-bi-savi-wlan-02.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
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This Internet-Draft will expire on October 5, 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................... 5
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....................................... 6
5.1.1.1. Candidate Binding............................. 6
5.1.1.2. CAPWAP Extension.............................. 7
5.1.1.3. Mobility Solution............................. 9
5.1.2. AC Filtering....................................... 9
5.2. Autonomous WLAN......................................... 9
6. Security Considerations..................................... 10
7. IANA Considerations ........................................ 10
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8. Conclusions ................................................ 10
9. Contributors ............................................... 10
10. Acknowledgments ........................................... 11
11. References ................................................ 11
11.1. Normative References.................................. 11
11.2. 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 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.
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
Duplicate Address Detection procedure must record its state as
"SLAAC".
Each entry in IP-MAC mapping table has its lifetime. 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
stations 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. IP-MAC mapping table and MAC-IP
mapping table can be maintained separately on different devices, but
they must be synchronized. We will specify the details in Section 4.
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.
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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.
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.
Different from wired network, 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 holds 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 deferent 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 station leaves this access point. The entries for all the
related MAC addresses MUST be deleted.
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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 on 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.
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 and perform address snooping. Packet
filtering will be performed also on 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.
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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 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... +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 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.
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
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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 using host IP message
element specified in Section 5.1.1.2. AC return 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 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 both address snooping and packet filtering. So all the
packets must be firstly be forwarded to AC. 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 procedures are
needed to establish the IP-MAC bindings. AC executes the procedure
specified in Section 4 for packet filtering.
Mobility within one AC does not trigger any binding migration.
Mobility between different ACs triggers binding migration. Home AC
deletes the binding when mobile host is disconnected, and foreign AC
requests the bound addresses with the associated MAC from Home AC.
CAPWAP extensions specified in Section 5.1.1.2 can be used for
communications between AC.
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
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pairs by consulting the local IP-MAC mapping table. No extra
procedures are needed to establish the IP-MAC bindings. FAT AP
executes the procedure specified in Section 4 for packet filtering.
Mobility between different FAT APs will trigger binding migration.
Home FAT AP deletes the binding when mobile host is disconnected, and
foreign FAT AP requests the bound addresses with the associated MAC
from Home FAT AP. 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.
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
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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.
[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: wangyou10@mails.tsinghua.edu.cn
Tao Lin
Hangzhou H3C Tech. Co., Ltd.
Beijing 100085
China
EMail: lintaog@gmail.com
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