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Network Working Group S. Krishnan
Internet-Draft Ericsson
Intended status: Standards Track Y. Sheffer
Expires: November 19, 2009 Check Point
N. Steinleitner
University of Goettingen
G. Bajko
Nokia
May 18, 2009
Guidelines for firewall vendors regarding MIPv6 traffic
draft-ietf-mext-firewall-vendor-01
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Abstract
This document presents some recommendations for firewall vendors to
help them implement their firewalls in a way that allows Mobile IPv6
signaling and data messages to pass through. This document describes
how to implement stateful packet filtering capability for MIPv6.
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. MIPv6 Firewall Primitives . . . . . . . . . . . . . . . . . . . 3
3.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Detecting and parsing the Mobility Header . . . . . . . . . 3
3.3. Parsing Mobility Options . . . . . . . . . . . . . . . . . 4
4. Allowing signaling response packets . . . . . . . . . . . . . . 4
5. Allowing data packets based on signaling . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
9. Normative References . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 9
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1. Requirements notation
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].
2. Introduction
Network elements such as firewalls are an integral aspect of a
majority of IP networks today, given the state of security in the
Internet, threats, and vulnerabilities to data networks. MIPv6
[RFC3775] defines mobility support for IPv6 nodes. Since firewalls
are not aware of MIPv6 protocol details, they will probably interfere
with the smooth operation of the protocol. The problems caused by
firewalls to Mobile IPv6 are documented in [RFC4487].
This document presents some recommendations for firewall vendors to
help them implement their firewalls in a way that allows Mobile IPv6
signaling and data messags to pass through. This document describes
how to implement stateful packet filtering capability for MIPv6.
Some Mobile IPv6 signalling messages require the use of encryption to
protect the confidentiality of the payload (e.g. the HoTI and HoT
messages between the MN and the HA). The other signalling messages
allow the use of encryption. If encryption is being used, it is not
possible to inspect the contents of the signalling packets. For
these messages to get through, a generic rule needs to be added in
the firewall to let ESP packets through without further inspection.
3. MIPv6 Firewall Primitives
3.1. Requirements
This document assumes that the firewalls are capable of deep packet
inspection at least until the mobility header. It also assumes that
the firewalls are capable of creating filters based on arbitrary
fields based on the contents of a signaling packet.
3.2. Detecting and parsing the Mobility Header
The Mobility Header is the basic primitive in all MIPv6 signaling
messages. Thus the firewalls need to be able to recognize the
presence of the mobility header and be able to parse the contents of
the Mobility Header. The MH is described in section 6.1 of [RFC3775]
and the format of the same is scribed in section 6.1.1 of [RFC3775].
Firewalls need to be able to at least understand the contents of the
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MH Type field that describes the type of signaling message carried.
3.3. Parsing Mobility Options
The Mobility Header can carry additional information in the form of
mobility options as described in section 6.2 of [RFC3775]. Some of
these mobility options need to be understood for proper creation of
state on the firewalls. Hence firewalls must be able to parse the
mobility options defined in [RFC3775].
4. Allowing signaling response packets
The MIPv6 signalling messages are usually performed as a request-
response pair. The request message is usually allowed by setting up
a static firewall rule to allow the traffic to pass through. The
response message on the other hand can be dynamically allowed if the
firewall can automatically setup a filter for the response packets
when the request packet passes through. This is not trivial, but
fortunately is straightforward. There are 3 message pairs that are
of importance to MIPv6 signaling. They are the BU/BA, HoTI/HoT and
CoTI/CoT pairs. When the first message in the pair traverses the
firewall in one direction, the firewall must setup a filter rule to
allow the second message through in the other direction.
Consider a packet that matches a static rule configured on a firewall
Destination Address: Address of HA
Next Header: 50 (ESP)
Mobility Header Type: 5 (BU)
This rule allows a binding update message from a MN to pass through
to the HA. Once a packet that matches this rule passes through the
firewall, the firewall must setup a dynamic filter for the return
packet
Source Address: Destination Address from Packet
Destination Address: Source Address from Packet
Next Header: 50 (ESP)
Mobility Header Type: 6 (BA)
This rule ensures that the return BA packet will pass through
unhindered. The rules can be generalized as summarized in the table
below.
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+---------------------------------+---------------------------------+
| Passing packet MH Type | Setup return filter with MH |
| | Type |
+---------------------------------+---------------------------------+
| Mobility Header Type:1(HoTI) | Mobility Header Type:3(HoT) |
| Mobility Header Type:2(CoTI) | Mobility Header Type:4(CoT) |
| Mobility Header Type:5(BU) | Mobility Header Type:6(BA) |
+---------------------------------+---------------------------------+
Table 1: Message Pairs in MIPv6
Such dynamic rules can be timed out after a configurable period
STATEFUL_PINHOLE_LIFETIME, unless renewed by new mobility messages.
This document recommends that the default value of
STATEFUL_PINHOLE_LIFETIME be set to 30 seconds.
These dynamic rules MUST be immediately deleted after the return
message passes through. e.g. Once a return HoT message for a HoTI
passes through, the pinhole must be immediately removed. The loss of
the HoT packet after passing the firewall needs to be handled by the
original MN retransmitting the HoTI message.
5. Allowing data packets based on signaling
Once the MIPv6 signaling completes, the data traffic can begin to
flow. The traffic filters for the data traffic can be inferred from
the contents of the signaling messages that setup the session. This
section describes how firewalls can intelligently setup filters for
data traffic based on signaling traffic.The following example
describes how to setup a filter for allowing incoming route optimized
messages from a CN to an MN after the MN sent a BU message to a CN.
When the BU message from MN to CN (MH Type 5) traverses through the
firewall the firewall extracts the home address (HoA) from the Home
Address Option (section 6.3 of [RFC3775]) of the packet.
The firewall adds the following rule in order to let the return
traffic pass.
Destination Address: Source Address of the packet (MN CoA)
Source Address: Destination Address of packet (CN)
Routing Header Type 2 Address: HoA
This pattern allows all route optimized traffic coming from the CN to
the MN to pass through.
Additionally, the firewall adds a second rule in order to let the
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data traffic from the MN to the CN pass through.
Source Address: Source Address of the packet (MN CoA)
Destination Address: Destination Address of packet (CN)
Next Header: IPv6 Destination Options Header(60)
Home Address Dest. Option: MN HoA
This pattern allows all route optimized traffic coming from the MN to
the CN to pass through.
A firewall protecting the HA can add the following rule on reception
of a HA binding update, in order to let the incoming bi-directional
tunneled traffic pass.
Destination Address: Source Address of the packet (MN HoA)
Source Address: Destination Address of packet (CN)
6. Acknowledgements
The authors would like to thank the following members of the MIPv6
firewall design team for contributing to this document: Hannes
Tschofenig, Hesham Soliman, Qiu Ying, and Vijay Devarapalli. The
authors would also like to thank William Ivancic, Ryuji Wakikawa,
Jari Arkko, Henrik Levkowetz, Pasi Eronen and Noriaki Takamiya for
their thorough reviews of the document and for providing comments to
improve the quality of the document.
7. IANA Considerations
This document does not require any IANA action.
8. Security Considerations
This document specifies recommendations for firewall vendors to allow
Mobile IPv6 traffic to pass through unhindered. This document
recommends a liberal setting of firewall rules so that all legitimate
traffic may be allowed to pass. This means that some malicious
traffic may be permitted by these rules. These rules may allow the
initiation of Denial of Service attacks against Mobile IPv6 capable
nodes (the MNs, CNs and the HAs).
One of the main goals of any firewall is to prevent unsolicited
traffic from entering the network. The proposed solution allows such
traffic into the network, albeit with a number of restrictions.
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In a typical enterprise environment, an administrator cannot
distinguish Mobile IPv6 capable nodes from other nodes. In such a
situation any node in the protected network may end up receiving
unsolicited packets from outside the firewall. The risk in this case
is that such packets could trigger unknown vulnerabilities in any of
these nodes, causing denial-of-service or worse attacks. This issue
is compounded in a mobile service provider environment by the risks
specific to such environments like endpoint battery exhaustion and
spectrum misuse.
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC4487] Le, F., Faccin, S., Patil, B., and H. Tschofenig, "Mobile
IPv6 and Firewalls: Problem Statement", RFC 4487,
May 2006.
Authors' Addresses
Suresh Krishnan
Ericsson
8400 Decarie Blvd.
Town of Mount Royal, QC
Canada
Phone: +1 514 345 7900 x42871
Email: suresh.krishnan@ericsson.com
Yaron Sheffer
Check Point
5 Hasolelim St.
Tel Aviv 67897
Israel
Email: yaronf@checkpoint.com
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Niklas Steinleitner
University of Goettingen
Lotzestr. 16-18
Goettingen
Germany
Email: steinleitner@cs.uni-goettingen.de
Gabor Bajko
Nokia
Email: gabor.bajko@nokia.com
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