Network Working Group S. Krishnan
Internet-Draft Ericsson
Intended status: Informational N. Steinleitner
Expires: April 11, 2009 University of Goettingen
Y. Qiu
Institute for Infocomm Research
G. Bajko
Nokia
October 8, 2008
Guidelines for firewall administrators regarding MIPv6 traffic
draft-ietf-mext-firewall-admin-00
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Abstract
This document presents some recommendations for firewall
administrators to help them configure their existing firewalls in a
way that allows in certain deployment scenarios the Mobile IPv6
signaling and data messages to pass through. For other scenarios,
the support of additional mechanisms to create pinholes required for
MIPv6 will be necessary. This document assumes that the firewalls in
question include some kind of stateful packet filtering capability.
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Home Agent behind a firewall . . . . . . . . . . . . . . . . . 4
4.1. Signaling between the MN and the HA . . . . . . . . . . . 5
4.2. IKEv2 signaling between MN and HA for establishing SAs . . 5
5. Correspondent Node behind a firewall . . . . . . . . . . . . . 5
5.1. Route optimization signaling between MN and CN through
HA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Route optimization signaling between MN and CN . . . . . . 6
5.3. Binding Update from MN to CN . . . . . . . . . . . . . . . 7
5.4. Route Optimization data traffic from MN . . . . . . . . . 7
6. Mobile Node behind a firewall . . . . . . . . . . . . . . . . 7
6.1. Signaling between MN and HA . . . . . . . . . . . . . . . 8
6.2. Signaling between MN and CN . . . . . . . . . . . . . . . 9
6.3. IKEv2 signaling between MN and HA for establishing SAs . . 9
7. Related documents . . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. Security Considerations . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 12
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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. Firewalls will
interfere with the smooth operation of the MIPv6 protocol unless
specific steps are taken to allow Mobile IPv6 signaling and data
messages to pass through the firewall. The problems caused by
firewalls to Mobile IPv6 are documented in [RFC4487].
This document presents some recommendations for firewall
administrators to help them configure their firewalls in a way that
allows the Mobile IPv6 signaling and data messages to pass through.
This document assumes that the firewalls in question include some
kind of stateful packet filtering capability. The static rules that
need to be configured are described in this document. In some
scenarios, the support of additional mechanisms to create pinholes
required for MIPv6 signalling and data traffic to pass through will
be necessary. A possible solution, describing the dynamic
capabilities needed for the firewalls to create pinholes based on
MIPv6 signalling traffic is described in a companion document
[MIP6FWVENDOR]. Other solutions may also be possible.
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. Abbreviations
This document uses the following abbreviations:
o CN: Correspondent Node
o CoA: Care of Address
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o CoTI: Care of Test Init
o HA: Home Agent
o HoA: Home Address
o HoTI: Home Test Init
o HoT: Home Test
o MN: Mobile Node
o RO: Route Optimization
o RRT: Return Routability Test
4. Home Agent behind a firewall
This section presents the recommendations for configuring a firewall
that protects a home agent.
+----------------+ +---+
| | | A |
| | +---+
| +----+ | External
| | HA | +----+ MN
| +----+ | FW | +---+
| Home Agent +----+ | B |
| of A | +---+
| | External
| | Node
+----------------+
Network protected
by a firewall
Figure 1: HA behind a firewall
For each type of traffic that needs to pass through this firewall,
recommendations are presented on how to identify that traffic. The
following types of traffic are considered
o Signaling between the MN and the HA
o IKEv2 signaling between MN and HA for establishing SAs
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4.1. Signaling between the MN and the HA
The signaling between the MN and HA is protected using IPSec ESP.
These messages are critical to the MIPv6 protocol and if these
messages are discarded, Mobile IPv6 as specified today will cease to
work. In order to permit these messages through, the firewall has to
detect the messages using the following patterns.
Destination Address: Address of HA
Next Header: 50 (ESP)
Mobility Header Type: 5 (BU)
This pattern will allow the BU messages from MNs to HA to pass
through.
4.2. IKEv2 signaling between MN and HA for establishing SAs
The MN and HA exchange IKEv2 signaling in order to establish the
security associations. The security associations so established will
later be used for securing the mobility signaling messages. Hence
these messages need to be permitted to pass through the firewalls.
The following pattern will detect these messages.
Destination Address: Address of HA
Transport Protocol: UDP
Destination UDP Port: 500
5. Correspondent Node behind a firewall
This section presents the recommendations for configuring a firewall
if a node behind it should be able to act as Mobile IPv6 CN.
+----------------+ +----+
| | | HA |
| | +----+
| | Home Agent
| +---+ +----+ of B
| |CN | | FW |
| | C | +----+
| +---+ | +---+
| | | B |
| | +---+
+----------------+ External Mobile
Network protected Node
by a firewall
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Figure 2: CN behind a firewall
For each type of traffic that needs to pass through this firewall,
recommendations are presented on how to identify that traffic. The
following types of traffic are considered
o Route optimization signaling between MN and CN through HA
o Route optimization signaling between MN and CN
o Binding Update from MN to CN
o Route Optimization data traffic from MN
5.1. Route optimization signaling between MN and CN through HA
Parts of the initial route optimization signaling has to pass through
the HA, namely the HoTI and the HoT messages. Without assistance,
the HoTI message from the HA to the CN is not able to traverse the
firewall. When only a few priviledged nodes (like servers) are
allowed to be contacted by outside nodes, then the following pattern
will allow the HoTI messages to reach these nodes:
Destination Address: CN Address
Mobility Header Type: 1 (HoTI)
where CN Address describes the address(es) of the priviledged
node(s). This pinhole allows the HoTI message from the HA to the CN
to traverse the firewall. The HoT message from the CN to the MN
through the HA can traverse the firewall without any assistance.
Hence no pinhole is required.
5.2. Route optimization signaling between MN and CN
Route Optimization allows direct communication of data packets
between the MN and a CN without tunnelling it back through the HA.
To get route optimization work, the MN has to send a CoTI message
directly to the CN, which response with a CoT message. However, a
stateful firewall would prevent the CoTI message to pass through as
there is no established state on the firewall. When only a few
priviledged nodes (like servers) are allowed to be contacted by
outside nodes, then the following pattern will allow the CoTI
messages to reach these nodes:
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Destination Address: CN Address
Mobility Header Type: 2 (CoTI)
where CN Address describes the address(es) of the priviledged
node(s).The CoT message from the CN to the MN can traverse the
firewall without any assistance. Hence no pinhole is required.
5.3. Binding Update from MN to CN
After successfully performing the return routability procedure, the
MN sends the BU to the CN and expects the BA. Since this BU does not
match any previous installed pinhole rules, an additional pinhole
with the following format is required.When only a few priviledged
nodes (like servers) are allowed to be contacted by outside nodes,
then the following pattern will allow the BU messages to reach these
nodes:
Destination Address: CN Address
Mobility Header Type: 5
where CN Address describes the address(es) of the priviledged
node(s).This allows the BU to traverse the firewall and the BA can
pass the firewall without any assistance. Therefore, the Binding
Update sequence can be performed successfully.
5.4. Route Optimization data traffic from MN
Also the Route Optimization data traffic from MN directly to the CN
can not traverse the firewall without assistance. A dynamically
created pinhole such as the one specified in [MIP6FWVENDOR] will
allow this traffic to pass.
6. Mobile Node behind a firewall
This section presents the recommendations for configuring a firewall
that protects the network a mobile node visiting.
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+----------------+ +----+
| | | HA |
| | +----+
| | Home Agent
| +---+ +----+ of A +---+
| | A | | FW | | B |
| +---+ +----+ +---+
|Internal | External
| MN | Node
| |
+----------------+
Network protected
by a firewall
Figure 3: MN behind a firewall
For each type of traffic that needs to pass through this firewall,
recommendations are presented on how to identify that traffic. The
following types of traffic are considered
o Signaling between MN and HA
o Route Optimization Signaling between MN and CN
o IKEv2 signaling between MN and HA for establishing SAs
6.1. Signaling between MN and HA
As described in Section 4.1, the signaling between the MN and HA is
protected using IPSec ESP. Currently, a lot of firewalls are
configured to block the incoming ESP packets. Moreover, from the
view of the firewall, both source and destination addresses of these
messages from/to mobile node are variable. Fortunately, for a
stateful firewall, if the initial traffic is allowed through the
firewall, then the return traffic is also allowed. A mobile node is
always the initiator for the BU. Since MN's CoA is not able to be
known in advance, the firewall can use following patterns to permit
these messages through.
Source Address: Visited subnet prefix
Destination Address: Address of HA
Next Header: 50 (ESP)
Mobility Header Type: 5 (BU)
This pattern will allow the Binding Update packets to pass through
the firewall. Then the return packets (BA from HA to MN) will also
able to pass through accordingly.
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6.2. Signaling between MN and CN
Route Optimization allows direct communication of data packets
between the MN and a CN without tunneling it back through the HA. It
includes 3 pairs of messages: HoTI/HoT, CoTI/CoT and BU/BA. The
first pair can pass through the firewall using the pattern described
in section 5.1. Here we discuss CoTI/CoT and BU/BA messages.
Following pattern permits these messages through the firewall.
Source Address: Visited subnet prefix
Mobility Header Type: 2 (CoTI)
Source Address: Visited subnet prefix
Mobility Header Type: 5 (BU)
This pattern allows the initial messages (CoTI and BU) from the MN to
the CN pass through the firewall. The return messages (CoT and BA)
from the CN to the MN can also passes through the firewall
accordingly.
6.3. IKEv2 signaling between MN and HA for establishing SAs
The MN and HA exchange IKEv2 signaling in order to establish the
security associations. The security associations so established will
later be used for securing the mobility signaling messages. Due to
variable source/destination IP addresses and MN always as initiator,
the following pattern will let the negotiation pass.
Source Address: Visited subnet prefix
Transport Protocol: UDP
Destination UDP Port: 500
7. Related documents
There are other IETF published documents that provide recommendations
for firewall configuration that can affect Mobile IPv6 messages.
[RFC4890] that provides recommendations for filtering ICMPv6 messages
(especially Section 4.3.2). [RFC4942] describes security issues
present in IPv6 and related protocols (especially Sections 2.1.2 and
2.1.15).
8. Acknowledgements
The authors would like to thank the following members of the MIPv6
firewall design team for contributing to this document: Hannes
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Tschofenig, Hesham Soliman, Yaron Sheffer, 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.
9. IANA Considerations
This document does not require any IANA action.
10. Security Considerations
This document specifies recommendations for firewall administrators
to allow Mobile IPv6 traffic to pass through unhindered. Since some
of this traffic is encrypted it is not possible for firewalls to
discern whether it is safe or not. This document recommends a
liberal setting so that all legitimate traffic can 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).
11. References
11.1. Normative References
[MIP6FWVENDOR]
Krishnan, S., Sheffer, Y., Steinleitner, N., and G. Bajko,
"Guidelines for firewall vendors regarding MIPv6 traffic",
draft-ietf-mext-firewall-vendor-0 (work in progress),
October 2008.
[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.
11.2. Informative References
[RFC4890] Davies, E. and J. Mohacsi, "Recommendations for Filtering
ICMPv6 Messages in Firewalls", RFC 4890, May 2007.
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[RFC4942] Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
Co-existence Security Considerations", RFC 4942,
September 2007.
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
Niklas Steinleitner
University of Goettingen
Lotzestr. 16-18
Goettingen
Germany
Email: steinleitner@cs.uni-goettingen.de
Ying Qiu
Institute for Infocomm Research
21 Heng Mui Keng Terrace
Singapore
Phone: +65-6874-6742
Email: qiuying@i2r.a-star.edu.sg
Gabor Bajko
Nokia
Email: gabor.bajko@nokia.com
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