MIP6 F. Le
Internet-Draft CMU
Expires: April 20, 2006 S. Faccin
B. Patil
Nokia
H. Tschofenig
Siemens
October 17, 2005
Mobile IPv6 and Firewalls: Problem statement
draft-ietf-mip6-firewalls-03.txt
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Copyright (C) The Internet Society (2005).
Abstract
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. Current IP
networks are predominantly based on IPv4 technology and hence
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firewalls have been designed for these networks. Deployment of IPv6
networks is currently progressing, albeit at a slower pace.
Firewalls for IPv6 networks are still maturing and in development.
Mobility support for IPv6 has been standardized as specified in RFC
3775. Given the fact that Mobile IPv6 is a recent standard, most
firewalls available for IPv6 networks do not support Mobile IPv6.
Unless firewalls are aware of Mobile IPv6 protocol details, these
security devices will interfere in the smooth operation of the
protocol and can be a detriment to deployment. This document
captures the issues that may arise in the deployment of IPv6 networks
when they support Mobile IPv6 and firewalls.
The issues are not only applicable to firewalls protecting enterprise
networks, but are also applicable in 3G mobile networks such as GPRS/
UMTS and cdma2000 networks.
The goal of this Internet draft is to highlight the issues with
firewalls and Mobile IPv6 and act as an enabler for further
discussion. Issues identified here can be solved by developing
appropriate solutions in the MIP6 WG.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Overview of firewalls . . . . . . . . . . . . . . . . . . . . 7
5. Analysis of various scenarios involving MIP6 nodes and
firewalls . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Scenario where the Mobile Node is in a network
protected by firewall(s) . . . . . . . . . . . . . . . . . 9
5.2. Scenario where the Correspondent Node is in a network
protected by firewall(s) . . . . . . . . . . . . . . . . . 11
5.3. Scenario where the HA is in a network protected by
firewall(s) . . . . . . . . . . . . . . . . . . . . . . . 15
5.4. Scenario where MN moves to a network protected by
firewall(s) . . . . . . . . . . . . . . . . . . . . . . . 15
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . . 20
Appendix A. Applicability to 3G Networks . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
Intellectual Property and Copyright Statements . . . . . . . . . . 23
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1. Introduction
Mobile IPv6 enables IP mobility for IPv6 nodes. It allows a mobile
IPv6 node to be reachable via its home IPv6 address irrespective of
any link that the mobile attaches to. This is possible as a result
of the extensions to IPv6 defined in the Mobile IPv6 specification
[1].
Mobile IPv6 protocol design also incorporates a feature termed as
Route Optimization. This set of extensions is a fundamental part of
the protocol that enables optimized routing of packets between a
Mobile Node and its correspondent node and therefore the performance
of the communication.
In most cases, current firewall technologies, however, do not support
Mobile IPv6 or are even aware of Mobile IPv6 headers and and
extensions. Since most networks in the current business environment
deploy firewalls, this may prevent future large-scale deployment of
the Mobile IPv6 protocol.
This document presents in detail some of the issues that firewalls
present for Mobile IPv6 deployment, as well as the impact of each
issue.
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2. Terminology
Return Routability Test (RRT): The Return Routability Test is a
procedure defined in RFC 3775 [1]. It is performed prior to the
Route Optimization (RO), where a mobile node (MN) instructs a
correspondent node (CN) to direct the mobile node's data traffic
to its claimed care-of address (CoA). The Return Routability
procedure provides some security assurance and prevents the misuse
of Mobile IPv6 signaling to maliciously redirect the traffic or to
launch other attacks.
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3. Abbreviations
This document uses the following abbreviations:
o CN: Correspondent Node
o CoA: Care of Address
o CoTI: Care of Test Init
o HA: Home Agent
o HoA: Home Address
o HoTI: Home Test Init
o MN: Mobile Node
o RO: Route Optimization
o RRT: Return Routability Test
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4. Overview of firewalls
The following section provides a brief overview of firewalls. It is
intended as background information so that issues with the Mobile
IPv6 protocol can then be presented in detail in the following
sections.
There are different types of firewalls and state can be created in
these firewalls through different methods. Independent of the
adopted method, firewalls typically look at five parameters of the
traffic arriving at the firewalls:
o Source IP address
o Destination IP address
o Protocol type
o Source port number
o Destination port number
Based on these parameters, firewalls usually decide whether to allow
the traffic or to drop the packets. Some firewalls may filter only
incoming traffic while others may also filter outgoing traffic.
According to Section 3.29 of RFC 2647 [2] stateful packet filtering
refers to the process of forwarding or rejecting traffic based on the
contents of a state table maintained by a firewall. These types of
firewalls are commonly deployed to protect networks from different
threats, such as blocking unsolicited incoming traffic from the
external networks. The following briefly describes how these
firewalls work since they can create additional problems with the
Mobile IPv6 protocol as described in the subsequent sections.
When a MN connects using TCP to another host in the Internet, it
sends a TCP SYN message to set up the connection. When that SYN
packet is routed through the firewall, the firewall creates an entry
in its state table containing the source IP address, the destination
IP address, the Protocol type, the source port number and the
destination port number indicated in that packet before forwarding
the packet to the destination. When an incoming message from the
external networks reaches the firewall, it searches the packet's
source IP address, destination IP address, Protocol type, source port
number and destination port number in its state table to see if the
packet matches the characteristics of a request sent previously. If
so, the firewall lets the packet pass. Otherwise, the packet is
dropped since it was not requested from inside the network.
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The firewall removes the state table entries either when the TCP
close session negotiation packets are routed through, or after some
configurable timeout period. This ensures that dropped connections
do not leave holes in the table.
For UDP, similar state is created. However, since UDP is
connectionless and the protocol does not have an indication of the
beginning nor the end of a session, the state is based only on
timers.
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5. Analysis of various scenarios involving MIP6 nodes and firewalls
The following section describes various scenarios involving MIP6
nodes and firewalls and also presents the issues related to each
scenario.
The Mobile IPv6 specifications define three main entities: the Mobile
Node (MN), the Correspondent Node (CN) and the Home Agent (HA). Each
of these entities may be in a network protected by one or many
firewalls:
o Section 5.1 analyzes the issues when the MN is in a network
protected by firewall(s)
o Section 5.2 analyzes the issues when the CN is in a network
protected by firewall(s)
o Section 5.3 analyzes the issues when the HA is in a network
protected by firewall(s)
The MN may also be moving from an external network, to a network
protected by firewall(s). The issues of this case are described in
Section 5.3.
Some of the described issues (e.g. Section 5.1 and Section 5.2) may
require modifications to the protocols or to the firewalls, and
others (e.g. Section 5.3) may require only appropriate rules and
configuration to be in place.
5.1. Scenario where the Mobile Node is in a network protected by
firewall(s)
Let's consider a MN A, in a network protected by firewall(s).
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+----------------+ +----+
| | | HA |
| | +----+
| | Home Agent
| +---+ +----+ of A +---+
| | A | | FW | | B |
| +---+ +----+ +---+
|Internal | External
| MN | Node
| |
+----------------+
Network protected
Figure 1: Issues between MIP6 and firewalls when MN is in a network
protected by firewalls
A number of issues need to be considered:
Issue 1: When the MN A connects to the network, it should acquire a
local IP address (CoA), and send a Binding Update to its Home
Agent to update the HA with its current point of attachment. The
Binding Updates and Acknowledgements should be protected by IPsec
ESP according to the MIPv6 specifications [1]. However, as a
default rule, many firewalls drop IPsec ESP packets because they
cannot determine whether inbound ESP packets are legitimate. It
is difficult or impossible to create useful state by observing the
outbound ESP packets. This may cause the Binding Updates and
Acknowledgements between the Mobile Nodes and their Home Agent to
be dropped.
Issue 2: Let's now consider a node in the external network, B, trying
to establish a communication with MN A.
* B sends a packet to the Mobile Node's home address.
* The packet is intercepted by the MN's Home Agent which tunnels
it to the MN's CoA [1].
* When arriving at the firewall(s) protecting MN A, the packet
may be dropped since the incoming packet may not match any
existing state. As described in Section 4, stateful inspection
packet filters e.g. typically drop unsolicited incoming
traffic.
* B will thus not be able to contact the MN A and establish a
communication.
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Even though the HA is updated with the location of a MN, firewalls
may prevent Correspondent nodes from establishing communications
when the MN is in a network protected by firewall(s).
Issue 3: Let's assume a communication between MN A and an external
node B. MN A may want to use Route Optimization (RO) so that
packets can be directly exchanged between the MN and the CN
without passing through the HA. However the firewalls protecting
the MN might present issues with the Return Routability procedure
that needs to be performed prior to using RO.
According to the MIPv6 specifications, the Home Test message of
the RRT must be protected by IPsec in tunnel mode. However,
firewalls might drop any packet protected by ESP, since the
firewalls cannot analyze the packets encrypted by ESP (e.g. port
numbers). The firewalls may thus drop the Home Test messages and
prevent the completion of the RRT procedure.
Issue 4: Let's assume that MN A successfully sends a Binding Update
to its Home Agent (resp. Correspondent nodes) - issues 1 (resp.
issue 3) solved - the subsequent traffic is sent from the HA
(resp. CN) to the MN's CoA. However there may not be any
corresponding state in the firewalls. The firewalls protecting A
may thus drop the incoming packets.
The appropriate states for the traffic to the MN's CoA need to be
created in the firewall(s).
Issue 5: When the MN A moves, it may move to a link that is served by
a different firewall. MN A might be sending a BU to its CN,
however incoming packets may be dropped at the firewall, since the
firewall on the new link that the MN attaches to does not have any
state that is associated with the MN.
The issues described above result from the fact that the MN is behind
the firewall. Consequently, the MN's communication capability with
other nodes is affected by the firewall rules.
5.2. Scenario where the Correspondent Node is in a network protected by
firewall(s)
Let's consider a MN in a network, communicating with a Correspondent
Node C in a network protected by firewall(s). There are no issues
with the presence of a firewall in the scenario where the MN is
sending packets to the CN via a reverse tunnel that is setup between
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the MN and HA. However firewalls may present different issues to
Route Optimization.
+----------------+ +----+
| | | HA |
| | +----+
| | Home Agent
| +---+ +----+ of B
| |CN | | FW |
| | C | +----+
| +---+ | +---+
| | | B |
| | +---+
+----------------+ External Mobile
Network protected Node
by a firewall
Figure 2: Issues between MIP6 and firewalls when a CN is in a network
protected by firewalls
The following issues need to be considered:
Issue 1: The MN, MN B, should use its Home Address, HoA B, when
establishing the communication with the CN (CN C) if the MN (MN B)
wants to take advantage of the mobility support provided by the
Mobile IPv6 protocol, for its communication with CN C. The state
created by the firewall protecting CN C is therefore created based
on the IP address of C (IP C) and the home address of the node B
(IP HoA B). The states may be created via different means and the
protocol type as well as the port numbers depend on the connection
set up.
Uplink packet filters (1)
Source IP address: IP C
Destination IP address: HoA B
Protocol Type: TCP/UDP
Source Port Number: #1
Destination Port Number: #2
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Downlink packet filters (2)
Source IP address: HoA B
Destination IP address: IP C
Protocol Type: TCP/UDP
Source Port Number: #2
Destination Port Number: #1
Nodes C and B might be topologically close to each other while B's
Home Agent may be far away, resulting in a trombone effect that
can create delay and degrade the performance. The MN B may decide
to initiate the route optimization procedure with Node C. Route
optimization requires the MN B to send a Binding Update to Node C
in order to create an entry in its binding cache that maps the MNs
home address to its current care-of-address. However, prior to
sending the binding update, the Mobile Node must first execute a
Return Routability Test:
* the Mobile Node B has to send a Home Test Init (HoTI) message
via its Home Agent and
* a Care of Test Init (COTI) message directly to its
Correspondent Node C.
The Care of Test Init message is sent using the CoA of B as the
source address. Such a packet does not match any entry in the
protecting firewall (2). The CoTi message will thus be dropped by
the firewall.
The HoTI is a Mobility Header packet, and the protocol type
differs from the existing states (2), the HoTI packet will also be
dropped.
As a consequence, the RRT cannot be completed and route
optimization cannot be applied. Every packet has to go through
the node B's Home Agent and tunneled between B's Home Agent and B.
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+----------------+
| +----+ HoTI (HoA) +----+
| | FW |X<---------------|HA B|
| +----X +----+
| +------+ | ^ CoTI & HoTI ^
| | CN C | | | dropped by FW |
| +------+ | | | HoTI
| | | |
| | | CoTI (CoA)+------+
| | +------------------| MN B |
+----------------+ +------+
Network protected External Mobile
by a firewall Node
Figure 3: Issues with Return Routability Test
Issue 2: Let's assume that the Binding Update to the CN is
successful, the firewall(s) might still drop packets
1. coming from the CoA, since these incoming packets are sent
from the CoA and do not match the Downlink Packet filter (2)
2. sent from the CN to the CoA if uplink packet filters are
implemented. The uplink packets are sent to the MN's CoA and
do not match the uplink packet filter (1).
The packet filters for the traffic sent to (resp. from) the CoA
need to be created in the firewall(s).
Requiring the firewalls to update the connection state upon
detecting Binding Update messages from a node outside the network
protected by the firewall does not appear feasible nor desirable,
since currently the firewall does not have any means to verify the
validity of Binding Update messages and to therefore securely
modify the state information. Changing the firewall states
without verifying the validity of the Binding Update messages
could lead to denial of service attacks. Malicious nodes may send
fake binding updates, forcing the firewall to change its state
information, and therefore leading the firewall to drop packets
from the connections that use the legitimate addresses. An
adversary might also use an address update to enable its own
traffic to pass through the firewall and enter the network.
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Issue 3: Let's assume that the Binding Update to the CN is
successful. The CN may be protected by different firewalls and as
a result of the MN's change of IP address, incoming and outgoing
traffic may pass through a different firewall. The new firewall
may not have any state associated with the CN and incoming packets
(and potentially outgoing traffic as well) may be dropped at the
firewall.
Firewall technology allows clusters of firewalls to share state
[3]. This, for example, allows the support of routing asymmetry.
However, if the previous and the new firewalls, where the packets
are routed through after the Binding Update has been sent, do not
share state, this may result in packets being dropped at the new
firewall. The new firewall not having any state associated with
the CN, incoming packets (and potentially outgoing traffic as
well) may be dropped at the new firewall.
5.3. Scenario where the HA is in a network protected by firewall(s)
In the scenarios where the Home Agent is in a network protected by
firewall(s), the following issues may exist:
Issue 1: If the firewall(s) protecting the Home Agent block ESP
traffic, many of the MIPv6 signaling (e.g. Binding Update, HoT)
may be dropped at the firewall(s) preventing MN(s) from updating
their binding cache and performing Route Optimization, since
Binding Update, HoT and other MIPv6 signaling must be protected by
IPsec ESP.
Issue 2: If the firewall(s) protecting the Home Agent block
unsolicited incoming traffic (e.g. as stateful inspection packet
filters do), the firewall(s) may drop connection set up requests
from CN, and packets from MN.
Issue 3: If the Home Agent is in a network protected by several
firewalls, a MN/CN's change of IP address may result in the
traffic to and from the Home Agent passing through a different
firewall that may not have the states corresponding to the flows.
As a consequence, packets may be dropped at the firewall.
5.4. Scenario where MN moves to a network protected by firewall(s)
Let's consider a HA in a network protected by firewall(s). The
following issues need to be investigated:
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Issue 1: Similarly to the issue 1 described in Section 5.1, the MN
will send a Binding Update to its Home Agent after acquiring a
local IP address (CoA). The Binding Updates and Acknowledgements
should be protected by IPsec ESP according to the MIPv6
specifications [1]. However, as a default rule, many firewalls
drop ESP packets. This may cause the Binding Updates and
Acknowledgements between the Mobile Nodes and their Home Agent to
be dropped.
Issue 2: The MN may be in a communication with a CN, or a CN may be
attempting to establish a connection with the MN. In both cases,
packets sent from the CN will be forwarded by the MN's HA to the
MN's CoA. However when the packets arrive at the firewall(s), the
incoming traffic may not match any existing state, and the
firewall(s) may therefore drop it.
Issue 3: If the MN is in a communication with a CN, the MN may
attempt to execute a RRT for packets to be route optimized.
Similarly to the issue 3, Section 5.1, the Home Test message which
should be protected by ESP may be dropped by firewall(s)
protecting the MN. Firewall(s) may as a default rule drop any ESP
traffic. As a consequence, the RRT cannot be completed.
Issue 4: If the MN is in a communication with a CN, and assuming that
the MN successfully sent a Binding Update to its CN to use Route
Optimization, packets will then be sent from the CN to the MN's
CoA and from the MN's CoA to the CN.
Packets sent from the CN to the MN's CoA may however not match any
existing entry in the firewall(s) protecting the MN, and therefore
be dropped by the firewall(s).
If packet filtering is applied to uplink traffic (i.e. traffic
sent by the MN), packets sent from the MN's CoA to the the CN may
not match any entry in the firewall(s) either and may be dropped
as well.
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6. Conclusions
Current firewalls may not only prevent route optimization but may
also prevent regular TCP and UDP sessions from being established in
some cases. This document describes some of the issues between the
Mobile IPv6 protocol and current firewall technologies.
This document captures the various issues involved in the deployment
of Mobile IPv6 in networks that would invariably include firewalls.
A number of different scenarios are described which include
configurations where the mobile node, correspondent node and home
agent exist across various boundaries delimited by the firewalls.
This enables a better understanding of the issues when deploying
Mobile IPv6 as well as providing an understanding for firewall design
and policies to be installed therein.
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7. Security Considerations
This document describes several issues that exist between the Mobile
IPv6 protocol and firewalls.
Firewalls may prevent Mobile IP6 signaling in addition to dropping
incoming/outgoing traffic.
If the firewall configuration is modified in order to support the
Mobile IPv6 protocol but not properly configured, many attacks may be
possible as outlined above: malicious nodes may be able to launch
different types of denial of service attacks.
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8. Acknowledgments
We would like to thank James Kempf, Samita Chakrabarti, Giaretta
Gerardo, Steve Bellovin, Henrik Levkowetz and Spencer Dawkins for
their valuable comments. Their suggestions have helped to improve
both the presentation and the content of the document.
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9. References
9.1. Normative References
[1] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
9.2. Informative References
[2] Newman, D., "Benchmarking Terminology for Firewall Performance",
RFC 2647, August 1999.
[3] Noble, J., Doug, D., Hourihan, K., Hourihan, K., Stephens, R.,
Stiefel, B., Amon, A., and C. Tobkin, "Check Point NG VPN-1/
Firewall-1 Advanced Configuration and Troubleshooting", Syngress
Publishing Inc. , 2003.
[4] Chen, X., Watson, M., and M. Harris, "Problem Statement for
MIPv6 Interactions with GPRS/UMTS Packet Filtering",
draft-chen-mip6-gprs-03 (work in progress), February 2005.
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Appendix A. Applicability to 3G Networks
In 3G networks, different packet filtering functionalities may be
implemented to prevent malicious nodes from flooding or launching
other attacks against the 3G subscribers. The packet filtering
functionality of 3G networks are further described in [4]. Packet
filters are set up and applied to both uplink and downlink traffic:
outgoing and incoming data not matching the packet filters is
dropped. The issues described in this document also apply to 3G
networks.
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Authors' Addresses
Franck Le
Carnegie Mellon University
5000 Forbes Avenue
Pittsburgh, PA 15213
USA
Email: franckle@cmu.edu
Stefano Faccin
Nokia Research Center
6000 Connection Drive
Irving, TX 75039
USA
Email: stefano.faccin@nokia.com
Basavaraj Patil
Nokia
6000 Connection Drive
Irving, TX 75039
USA
Email: Basavaraj.Patil@nokia.com
Hannes Tschofenig
Siemens
Otto-Hahn-Ring 6
Munich, Bavaria 81739
Germany
Email: Hannes.Tschofenig@siemens.com
URI: http://www.tschofenig.com
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