Network Working Group K. Nielsen
INTERNET-DRAFT Ericsson
M. Morelli
Expires: April 4, 2005 Telecom Italia Lab
J. Palet
Consulintel
J. Soininen
Nokia
J. Wiljakka
Nokia
October 5, 2004
Goals for Zero-Configuration Tunneling in 3GPP
<draft-nielsen-v6ops-3GPP-zeroconf-goals-00.txt>
Status of this memo
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Abstract
Various types of IPv6-IPv4 tunneling are envisaged to be required in
the transition period from IPv4 networking to IPv6 networking, or
more precisely, in the transition period from IPv4 only networking to
dual or mixed IPv6 and IPv4 networking.
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Zero-Configuration Tunneling is the term used for a minimalistic
IPv6-in-IPv4 automatic tunneling mechanism that could be used by a
Service Provider to offer IPv6 connectivity to its customers in early
phases of IPv4 to IPv6 transition.
This document describes the set of goals to be fulfilled by a Zero-
Configuration Tunneling protocol in the 3GPP environment.
Table of Contents
1. Introduction.....................................................3
2. Terminology......................................................4
3. Scope and Limitations............................................5
3.1. IPv6 address allocation, Scope and Limitations:.............5
3.2. IPv6 tunnel link characteristics, Scope and Limitations:....5
4. Assumptions and Prerequisites....................................6
4.1. Applicability Assumptions...................................6
4.2. 3GPP Prerequisites..........................................6
5. Timing...........................................................7
6. Goals............................................................7
6.1. Simplicity..................................................8
6.2. Automated IPv6-in-IPv4 tunnel establishment.................8
6.3. Use native when available...................................9
6.4. Easy to deploy and Easy to Phase-out with no modifications on
existing equipment...............................................9
6.5. Tunnel Server End-Point Auto-Discovery.....................10
6.6. Address Assignment.........................................10
6.7. Tunnel Link Sustainability.................................10
6.8. Tunnel End-Point Reachability Detection....................11
6.9. Private and public IPv4 addresses..........................11
6.10. Scalability, Load Balancing...............................11
6.11. Security..................................................11
7. Non Goals.......................................................11
7.1. NAT and Firewall Traversal.................................12
7.2. IPv6 DNS...................................................12
7.3. Extensibility..............................................12
7.4. Registration burden........................................12
8. Stateful or Stateless...........................................12
9. Security Considerations.........................................13
9.1. Threats to existing network infrastructures................13
9.2. Threats to nodes implementing Zero-Configuration Tunneling.14
9.2.1. Threats to end-hosts..................................14
9.2.2. Threats to Tunnel Servers.............................15
9.2.2.1. Tunnel State related risks.......................15
9.2.2.2. Traffic related risks............................15
9.2.2.3. Packet Delivery related threats..................16
9.3. Implications of Direct Tunneling...........................16
10. Acknowledgments................................................17
11. Authors Addresses..............................................17
12. Changes from draft-nielsen-v6ops-zeroconf-goals-01.txt.........18
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13. Informative References.........................................18
Appendix A Out of Scope............................................19
1. Introduction
The IETF v6ops Working Group has identified and analyzed deployment
scenarios for IPv4/IPv6 transition mechanisms in various stages of
IPv6 deployment and IPv6 and IPv4 coexistence.
This work has been carried out for a number of different network
environments each with their particular characteristics: Enterprise,
ISP, Unmanaged and 3GPP networks, see e.g., [2], [3] and [4].
The work has identified a need for automatic IPv6-in-IPv4 tunneling
mechanisms that provide bidirectional IPv6-in-IPv4 tunneled
connectivity between dual stack end-nodes located at an IPv4-only
access network and dual-stack tunnel servers located at IPv6-IPv4
network boundaries within the Service Providers network.
The term Zero-Configuration Tunneling is used to denote a simplistic
automatic IPv6-in-IPv4 tunneling mechanism.
Zero-Configuration Tunneling is intended to provide a basic set of
tunneling features only, and intentionally so. The scope of Zero-
Configuration Tunneling is not to provide emulation of the full suite
of native IPv6 connectivity functions as defined by [7], [8] and [9];
rather the focus is to provide a minimal set of features required for
automatic establishment of IPv6 connectivity.
IPv6-in-IPv4 tunneling is envisaged to be deployed in 3GPP networks
as an initial and temporary mechanism to provide limited and basic
IPv6 connectivity services only. The IPv6-in-IPv4 tunneling mechanism
demanded by the 3GPP environment falls within the realm of Zero-
Configuration Tunneling.
Native IPv6 like 3GPP connectivity services, e.g. services including
flexible charging and quality of service on demand, will in 3GPP
environments be feasible by virtue of true native IPv6 only. This is
due to the interrelation between the native IPv6 3GPP service and
various 3GPP signaling interfaces. The latter which is not envisaged
upgraded to support the IPv6-in-IPv4 tunneling situation.
It is important to note that the IPv6 connectivity provided by 3GPP
Zero-Configuration IPv6-in-IPv4 tunneling does not compare with the
native IPv6 3GPP connectivity in terms of the services offered. This
differentiates the 3GPP IPv6-in-IPv4 tunneling transition case
somewhat from some of the other transition scenarios considered in
the IETF v6ops WG and unlike some of these scenarios, the 3GPP IPv6-
in-IPv4 tunneling deployment case is not a case of progressive and
gradual roll out of native IPv6-like services. Rather, Zero-
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Configuration tunneling will in the 3GPP environment be deployed for
the following purposes:
- To provide temporary provisioning of basic IPv6 services, which
users may deploy for the simplest IPv6 services only.
- To allow an Operator, possibly a native IPv6 enabled Operator,
to provide basic IPv6 services to users roaming into foreign
networks which supports IPv4 bearer connectivity only.
Unless otherwise specified then in this document the reference, IPv6-
in-IPv4 encapsulation as defined in [1], refers to the aspects of
Protocol-41 encapsulation related to IPv4 header construction (except
for source and destination address determination), MTU and
Fragmentation, Hop Limits and ICMP handling as detailed in Section
3.1-3.6 of [1]. The particular aspects of Configured IPv6-In-IPv4
Tunneling in the areas of IPv4 source and destination address
determination, tunnel link characteristics and IPv6 Neighbor
Discovery operation are not intended referred to by the above
reference.
2. Terminology
Zero-Configuration Tunneling site:
A logical IPv4 network over which IPv6 connectivity is provided to
dual-stack nodes by means of Zero-Configuration Tunneling.
Tunnel End-point:
A dual-stack node performing IPv6-in-IPv4 tunnel
encapsulation/decapsulation in accordance with Zero-Configuration
Tunneling.
Tunnel Server:
A dual-stack server node with IPv6 connectivity and which provides
IPv6 connectivity to client nodes by performing IPv6-in-IPv4 tunnel
encapsulation/decapsulation to/from client nodes in accordance with
Zero-Configuration Tunneling.
A Tunnel Server is likely to be a dual-stack router.
Tunnel Client:
A dual-stack node that obtains IPv6 connectivity by means of Zero-
Configuration Tunneling. A tunnel client relies on IPv6-in-IPv4
tunnel encapsulation/decapsulation to/from Tunnel Servers for IPv6
communications to native IPv6 nodes.
Direct Tunneling:
Direct tunneling here refer to the case where end-hosts located
within the same Zero-Configuration Tunneling site may circumvent the
Tunnel Server and communicate directly using the tunnel protocol.
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3. Scope and Limitations
The scope of Zero-Configuration Tunneling in the 3GPP network
environment is restricted to an absolute minimal set of functions
required to provide automatic IPv6 connectivity establishment to dual
stack nodes by means of IPv6-in-IPv4 encapsulation as defined in [1]
to Tunnel Servers under the assumptions and prerequisites described
in Section 4.
Zero-Configuration Tunneling in the 3GPP network environment does not
attempt to provide emulation of the full set of native IPv6
connectivity functions as defined by [7], [8] and [9].
3.1. IPv6 address allocation, Scope and Limitations:
The primary goal of 3GPP Zero-Configuration Tunneling is to provide
IPv6 connectivity to nodes on an individual basis. By this it is
meant that it is only an explicit goal to have a /128 address
allocated for global connectivity on the tunnel link. As such optimal
IPv6 connectivity provisioning in Personal Area Network (PAN)
scenarios is not explicitly within the scope of Zero-Configuration
Tunneling.
It is not explicitly within the scope of Zero-Configuration Tunneling
in the 3GPP network environment to support usage of privacy IPv6
extensions as defined in [12].
It is not explicitly within the scope to support usage of IPv6
multicast.
No goals are defined as to how address configuration should be
performed. This may be done based on legacy stateless or stateful
IPv6 address configuration mechanisms or by some altogether different
mechanism particular to the zero-configuration solution.
3.2. IPv6 tunnel link characteristics, Scope and Limitations:
Direct tunneling is neither an explicit goal nor explicitly excluded
in Zero-Configuration Tunneling in the 3GPP network environment.
It is not an explicit requirement for the 3GPP Zero-Configuration
tunnel link to support IPv6 link-local multicast.
The tunnel protocol should allow for the formation of a link-local
address on the tunnel link. Though no particular usage of such an
address is explicitly demanded by the goals set forward here.
It is an explicit goal that nodes attached to a tunnel link must be
able to ascertain the reachability of neighbors with which they are
communicating (or wish to start communicate). This may be achieved
using IPv6 Neighbor Discovery mechanism ([13]) based on unicast link-
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local packet exchanges (or link-local multicast if such is supported)
but it may also be achieved by altogether different mechanisms.
4. Assumptions and Prerequisites
4.1. Applicability Assumptions
The aim of the document is to define the set of goals to be fulfilled
by 3GPP Zero-Configuration Tunneling when the following assumptions
are made on the 3GPP deployment environment:
- IPv4 source addresses spoofing within the Zero-Configuration
Tunneling site is prevented.
- The Zero-Configuration Tunneling site is protected from
protocol-41 encapsulated packets arriving from external IPv4
networks.
- At least one authoritative DNS server is IPv4-enabled and at
least one recursive DNS server supports IPv4. Further IPv4 DNS
Server discovery is provided by already existing means/means
outside the scope of the tunnel protocol.
- The user is being authenticated to the network by means external
to the tunneling protocol and other than that no additional
authentication/registration mechanisms are required.
Plus in addition:
- There are no NATs in between the tunnel endpoints in the Zero-
Configuration Tunneling site.
- The Zero-Configuration Tunneling network is fully penetrable for
intra-site IPv6-in-IPv4 Protocol 41 traffic.
Finally, it is a prerequisite that the tunnel protocol must work in
IPv4 network environments, as the 3GPP network environment, where
IPv4 multicast is not provided.
The above assumptions are readily applicable to the 3GPP tunneling
transition scenario described in [4], section 3.1. The specific
transition scenario considered there and here is the scenario where a
3GPP UE deploys IPv6-in-IPv4 tunneling towards a Tunnel Server
located in its Home Operators network, this regardless of whether the
UE is located at an IPv4-only segment of its Home Operators network
or at an IPv4-only segment of a Foreign Operators network. In both
cases, it is assumed that the 3GPP UE is attached to the logical IPv4
network of its Home Operator, i.e., the Home Operator provides the
IPv4 address and the logical first hop link, read the IPv4 PDP
context, is terminated at a GGSN of its Home Operator.
4.2. 3GPP Prerequisites
3GPP Zero-Configuration Tunneling must work over 3GPP wireless
networks. When considering the characteristics of 3GPP network links
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and mobile terminals / User Equipment (UE), the following points need
to be taken into account:
- Link bandwidth (tunnel overhead / usage cost)
- Link latency
- UE battery power and derived implications on memory and
processing power
It is thus an explicit requirement for 3GPP Zero-Configuration
Tunneling to comply well with the constrained conditions put on the
above parameters by the 3GPP environments. The latter which commonly
is recognized as translating into requirements for the protocol to
operate with a limited number of message exchanges, small packet
sizes and simple message processing.
In this context it is note worthy that average round trip times in
3GPP networks can be in the size of 0.2 to 1.5 seconds (0.2 to 0.8
for 3G, 0.8 to 1.5 for 2.5G). This fact alone illustrates the need to
keep the number of message exchanges required for tunnel
initialization at an absolute minimum.
Here we shall refer to a protocol as being lightweight when its
demands on message exchanges, packet sizes and message processing
complexity are sufficiently light for it to be readily applicable in
environments characterized by the constrained conditions of 3GPP
networks (as described above).
As a mean to ensure that the protocol be lightweight it is considered
preferable for the protocol to provide a simple set of functions
only, even if it provides only a basic IPv6 service compared to the
native one. It is although acknowledged that additional functionality
doesn't necessarily automatically add complexity to the demands on
the aforementioned parameters.
5. Timing
For the purpose of 3GPP deployment it is a prerequisite that this
tunneling protocol is provided within a very restrictive timescale.
3GPP Release 6 documents, which ideally should refer to an
appropriate solution, are being finalized at the time of writing of
this document.
Trial deployments, in which zero-configuration type of IPv6
connectivity is provided in 3GPP environments, are starting up using
experimental protocols at the time of writing this document.
6. Goals
The goals to be achieved by Zero-Configuration Tunneling in the 3GPP
network environment are detailed in the following subsections.
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6.1. Simplicity
By simplicity, we understand a tunnel protocol that is easy to
implement in the targeted environment. Additionally, the protocol
should provide a reasonable, limited set of basic IPv6 connectivity
features.
Further by simplicity we imply that the protocol must be lightweight.
6.2. Automated IPv6-in-IPv4 tunnel establishment
The protocol should provide for the set up of IPv6-in-IPv4 tunnels,
based on IPv6-in-IPv4 encapsulation as defined in [1], from dual-
stack nodes, attached to IPv4-only networks, to Tunnel Servers.
The IPv6-in-IPv4 tunnels and the IPv6 connectivity must be
established in an automated manner, i.e., without requiring manual
intervention at any of the tunnel end-points at tunnel establishment
time.
The mechanism must be fully dynamic in the sense that it must not
require IP address information such as the IPv4 address of a Tunnel
Server and/or the IPv6 address(es) to use for IPv6 connectivity to be
configured on the Tunnel Clients beforehand.
Comment:
This goal is set to ensure that tunneled IPv6 connectivity can be
established in an automated manner by invocation of the Zero-
Configuration Tunneling function on an IPv4 network link.
For IPv6 connectivity to be established automatically, processes
within the node must be responsible for automatic invocation of the
Zero-Configuration Tunneling function when appropriate. The operation
of such activation - and deactivation - processes, as well as the
indicators on which such mechanisms may rely to determine the
appropriateness of tunneling, is not considered to be part of the
tunnel protocol processing per se and is considered to be an issue
for the node implementers.
Generally speaking, however, it is anticipated that such processes
will operate on the knowledge of whether IPv6 connectivity can be
established or not, for a 3GPP UE specifically whether IPv6 PDP
context activation succeeds or not.
No goals are set as to whether Zero-Configuration Tunneling should be
activated as default when native IPv6 connectivity is not available
or only by an applications demand for (tunneled) IPv6 connectivity.
As the general PDP context activation policies of an UE, e.g., see
the considerations given in Section 3.1 of [4], this is considered
determined by implementers, application developers and operators.
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Further refinements of how the automated process should be carried
out, and of the nature of the (IPv6) connectivity that should be
provided, is given in some of the subsequent goals.
6.3. Use native when available
The protocol must in no way restrict the native IPv6 capabilities of
the client node.
The node should not initiate Zero-Configuration Tunneling when native
IPv6 connectivity is available.
Comment:
The fact that a node should not initiate Zero-Configuration Tunneling
when native IPv6 connectivity is available is not considered to be a
functional requirement on the tunnel protocol per se. Rather it is
related to the activation and deactivation of the Zero-Configuration
Tunneling function.
On a 3GPP UE this translates into saying that the PDP context and
Zero-Configuration Tunneling activation policies implemented on the
UE should ensure that activation of IPv6 PDP contexts (when possible)
take precedence over activation of Zero-Configuration Tunneling over
IPv4 PDP contexts.
The extend to which a 3GPP UE may try for native IPv6 availability,
i.e., attempt for IPv6 PDP context activation, while moving around,
is, as the general PDP context activation policies of an UE, left to
be determined by UE implementers, application developers and
operators. Possible choices could be to attempt for IPv6 PDP context
activation once every time the IPv4 connectivity changes (e.g., IPv4
PDP context deactivation due to roaming out of operator range) or,
once every time a new IPv6 connectivity request is received from an
application. Attempts for IPv6 PDP context activation could in
principle also be done on the basis of Routing Area changes (change
of SGSN).
6.4. Easy to deploy and Easy to Phase-out with no modifications on
existing equipment
The tunnel protocol should be easy to deploy into the existing IPv4
and IPv6 network infrastructure.
The tunnel protocol should have no major impact on protocols and
infrastructure nodes deployed in existing infrastructures providing
IPv4 and native IPv6 connectivity.
The tunnel protocol should coexist and work seamlessly together with
any native IPv6 infrastructure that gradually may be implemented in
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the network. The tunnel protocol should have no negative implications
on how such are implemented.
The tunnel protocol must be easy to take out of service once native
IPv6 is available.
6.5. Tunnel Server End-Point Auto-Discovery
The tunnel protocol must provide a mechanism for automated end-point
discovery by the virtue of which end-hosts automatically and at run-
time can determine the IPv4 addresses of available Tunnel Servers.
The discovery mechanism should rely on intrinsic services, read
services already universally deployed, to the particular network
environment. It should not require the addition of additional IP
network infrastructure elements for this function only.
Comment: The analysis done in [6] may apply.
6.6. Address Assignment
The tunnel protocol must allow for the assignment of at least one
globally routable (/128) IPv6 unicast address to use for tunneled
IPv6 connectivity over the link provided by the Zero-Configuration
Tunneling mechanism.
It is preferable that the address assignment provides a stable
address, that is, an address that can be used for IPv6 connectivity
for a certain amount of time rather than solely one address per
higher layer session initiation.
6.7. Tunnel Link Sustainability
The tunnel link established in between a host deploying Zero-
Configuration Tunneling and an associated Tunnel Server should be
expected to remain in administrative active state for the lifetime of
the IPv6 address provided to the host.
The tunnel protocol must not mandate keep-alive messages to be
transmitted by the host simply in order to sustain tunnel link
connectivity.
Motivation: The fact that a 3GPP terminal, for the single purpose of
transmitting keep-alive messages, could have to wake up the radio
periodically, send a packet over the radio and possibly wait for
response is undesirable for the following reasons:
- The terminal cannot, as otherwise anticipated, be in dormant
mode all the time it is idle. This has severe implications for
the battery consumption of the device.
- Radio resources are costly and sparse and consequently not to be
used for what is considered to be unnecessary traffic.
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6.8. Tunnel End-Point Reachability Detection
The tunnel protocol must allow for means for one tunnel end-point to
verify the reachability of other tunnel end-points towards which it
intends to send packets.
The unicast neighbor reachability discovery functions provided by
IPv6 Neighbor Discovery ([13]), i.e., unicast NS/NA exchanges, should
be supported on the tunnel link.
6.9. Private and public IPv4 addresses
The tunnel protocol must work over IPv4 sites deploying both private
and public IPv4 addresses.
Furthermore, the tunnel protocol should work with both dynamic and
static IPv4 address allocation.
Motivation: Private IPv4 addresses are widely used in current 3GPP
networks.
6.10. Scalability, Load Balancing
In order to ensure the scalability of the tunnel service, in terms of
not limiting the number of simultaneous connections to the service
and consequently limiting possible service denial situations, it
should be possible for a Service Provider to load-balance those
connections among several available Tunnel Servers.
Load balancing should be planned already during the early phases of
deployment. Given adequate planning it should be possible for a
Service Provider to seamlessly deploy additional Tunnel Servers in
order to support an increased amount of Tunnel Clients.
Comment: This may be achieved using load-balancing functions provided
by the Tunnel Server End-point Discovery mechanism as detailed in
[14].
6.11. Security
The tunnel protocol should not impose any new vulnerability to the
existing 3GPP network infrastructure.
The tunnel protocol should not impose any new vulnerability to the
nodes implementing the tunnel protocol than what is already present
in existing multi-access IPv6 networks, where multiple hosts are
served by the same router or possibly multiple routers.
7. Non Goals
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Non-goals of 3GPP Zero-Configuration Tunneling are detailed in the
following subsections.
With the term Non-goals we refer to features that generally are
believed to be applicable to tunneling, but which are not among the
minimal set of required features of 3GPP Zero-Configuration
Tunneling. The latter primarily because of the assumptions made on
the applicability environments for 3GPP Zero-Configuration Tunneling,
e.g., see Section 4.
7.1. NAT and Firewall Traversal
NAT and Firewall traversal is not required due to the assumptions on
the applicability environment.
Moreover to minimize the tunneling overhead applied to the packets as
well as in order to minimize the number of tunnel set-up signaling
messages exchanged on the link, it is preferable that the protocol
does not deploy the UDP encapsulation techniques, on which mechanisms
able to traverse NATs and Firewalls normally rely.
7.2. IPv6 DNS
By virtue of the assumptions on the applicability environments, the
dual stack end-hosts can use IPv4 DNS discovery mechanisms and IPv4
transport for DNS services.
Given that IPv4 based DNS services are already available, it is not
considered a requirement that the end-host should be able to deploy
IPv6 based DNS services. Consequently, the tunnel protocol does not
need to provide IPv6 DNS discovery mechanisms.
7.3. Extensibility
As a minimal tunneling mechanism Zero-Configuration Tunneling targets
IPv6 connectivity provisioning only. The protocol does not need to be
readily extendable to other encapsulation mechanisms, e.g., IPv4-in-
IPv6.
7.4. Registration burden
Tunnel service registration is not required due to the assumptions on
the applicability environment.
In order to keep the simplicity and minimize the tunnel overhead it
is desirable that the tunnel protocol not in itself (e.g., in order
to meet the goals put forward in this document) mandates
authenticated registration of the user.
8. Stateful or Stateless
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By a stateful mechanism we mean a mechanism that require the Tunnel
Server to maintain tunnel state per client it serves.
Tunnel state here is considered to be any parameter kept by the
server per client and without which the server is unable to serve the
client (receive packets from/send packets to).
Tunnel state must be distinguished from state used to optimize the
packet delivery function of the tunnel server and which is kept in a
fixed or upper limited amount of memory space, such as, e.g.,
reachability information.
It should be emphasized that this document makes no deliberate
assumptions on whether a Zero-Configuration Tunneling solution should
be based on a stateful or stateless Tunnel Server mechanism. Indeed
it is anticipated that the goals of zero-configuration as put forward
here could be served both by a stateless as well as by a stateful
mechanism.
9. Security Considerations
It is considered reasonable to assume that the following assumptions
of Section 4 are valid in the particular 3GPP network environment:
- IPv4 source addresses spoofing within the Zero-Configuration
Tunneling site is prevented.
- The Zero-Configuration Tunneling site is protected from
protocol-41 encapsulated packets arriving from external IPv4
networks.
It is worthwhile to note that together these assumptions imply that
the IPv4 source of all protocol-41 tunneled packets is legitimate.
9.1. Threats to existing network infrastructures
As stated in Section 6.11 the tunnel protocol should not impose any
new vulnerability to the existing network infrastructure.
The following have been identified as potential threats opened up for
by the deployment of Zero-Configuration Tunneling:
- As the tunnel service is un-authenticated (not registered) it
may be possible to use a tunnel server to reflect tunneled
packets into the network, similar to the 6to4-reflection attacks
identified in [10].
- The Zero-configuration site must be kept fully penetrable for
intra-site IPv6-in-IPv4 protocol-41 encapsulated packets. This
may open up for threats to end-hosts that rely on the network
infrastructure to filter out bogus protocol-41 encapsulated
packets.
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- Zero-configuration tunneling may open up for threats to other
mechanisms in the network that rely on Protocol-41
encapsulation.
Detailed analysis of the validity of these threats will have to
depend on the particular Zero-Configuration solution. In general it
could be noted that attacks based on the above threats largely should
be preventable if the end-hosts in the network implement appropriate
drop policies, either simple drop all protocol-41 policies or more
differentiated policies based, e.g., on source addresses.
The only known additional protocol-41 based mechanism that may be
deployed in the 3GPP environment are Configured Tunnels ([1]) and in
this case unauthorized packets should be dropped by the Configured
Tunnel implementation.
9.2. Threats to nodes implementing Zero-Configuration Tunneling
The following considerations apply to the situation where Zero-
Configuration Tunneling is deployed in between tunnel servers and
end-hosts only.
Special security considerations for the usage of Zero-Configuration
Tunneling for direct tunneling in between end-hosts is given in
Section 9.3.
As stated in Section 6.11 the tunnel protocol should not impose any
new vulnerability to the nodes implementing the tunnel protocol than
what is already present in existing multi-access IPv6 networks where
multiple hosts are served by the same router or possible multiple
routers.
Here it is implicitly assumed that the tunnel server(s) take the role
of default routers and the end-nodes using Zero-Configuration
Tunneling for IPv6 connectivity the role of hosts in multi-access
environments.
9.2.1. Threats to end-hosts
Given that all IPv4 sources of protocol-41 tunneled packets can be
assumed to be legitimate, threats stemming from encapsulated packets
sourced by nodes (addresses) other than nodes (addresses) which the
end-hosts recognize as tunnel servers (identified by addresses) can,
if not already an intrinsic part of the Zero-Configuration protocol,
easily be mitigated by the implementation of appropriate
differentiated (source addresses) drop policies in the end-hosts,
i.e., accept only if source is tunnel server.
In current multi-access IPv6 networks hosts need to trust on the
benevolence of their default routers as well as hosts must trust that
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anyone impersonating as a router is indeed one, see, e.g., the trust
models and threats described in [11].
Future multi-access IPv6 networks may rely on SEND mechanisms, i.e.,
mechanisms developed in the SEND WG in order to mitigate the threats
described in [11], to establish a trust relations ship in between
host and routers.
Given that IPv4 source address spoofing is not possible in Zero-
Configuration Tunneling sites, then
- for an end-host to trust that packets it perceives as stemming
from tunnel servers do actually stem from such - as well as รป
- for an end-host to trust on the benevolence of its tunnel
servers,
it suffices that a trustworthy tunnel server end-point discovery
mechanism, read discovery of benevolent tunnel servers IPv4
address(es), is implemented.
In open environments, such as indeed the 3GPP environment, it is
assumed a prerequisite that a trustworthy Zero-Configuration tunnel
server end-point discovery mechanism is implemented.
9.2.2. Threats to Tunnel Servers
Zero-Configuration Tunneling may be deployed over very large IPv4
sites with low density of active tunnel clients but with a very high
number of dormant, but potential tunnel clients. Therefore Denial of
Service prevention by strict over provisioning of Tunnel Server
capacity is unlikely to be performed.
9.2.2.1. Tunnel State related risks
If the Tunnel Server relies on state to be kept per tunnel client
that it serves, the server risks resource exhaustion.
In this situation it is a security prerequisite that no node, whether
located within or outside the Zero-Configuration Tunneling site, can
initiate initialization of tunnel state for other entities than
itself.
Further it is a security prerequisite that the amount of tunnel
state, e.g. one tunnel per client only, created and maintained per
Tunnel Client, identified by e.g. its IPv4 address, is limited.
Given these prerequisites, then for tunnel server resource exhaustion
by tunnel state creation to be categorized as a security threat,
rather than a case of under provisioning, requires a large number of
tunnel clients to operate in co-action. This is thus not considered a
plausible threat.
9.2.2.2. Traffic related risks
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INTERNET-DRAFT Zeroconf Tunneling Goals October, 2004
Tunnel encapsulation is recognized as being more resource demanding
than mere packet forwarding. Given the same traffic load a Tunnel
Server must thus be more generously provisioned that a corresponding
router for it not to be more likely to get overthrown by large
unexpected amounts of traffic than the router.
The authors have found no plausible treats to the tunnel service, due
to large unexpected amounts of traffic needing encapsulation, which
can be classified as a security threat rather than a case of under
provision. This regardless of whether the traffic is due to a surge
in the density of active tunnel clients or due to a surge in the
traffic streams set-up by active clients.
9.2.2.3. Packet Delivery related threats
One potential risk related to packet delivery has been identified.
This risk is the equivalent of the threat to routers in multi-access
environments described in [11], Section 4.3.2.
The risk is associated with the special case where the tunnel
protocol requires special resource demanding and/or temporary state
creation actions to be taken by the Tunnel Server for delivery of
packets destined for not recently addressed Tunnel Clients. The
situation where such actions must be performed for all packets at all
times is considered to be unlikely. The actions required could be
buffering of packets while the reachability of the destined node is
being verified.
In case a malicious node (located either within or outside the zero-
configuration site) is able to continuously send packets to
continuously changing nodes, which by the Tunnel Server is perceived
as being existing or potential client nodes, the malicious node may
be able to exhaust the Tunnel Servers capability of delivering
packets by saturating the packet buffering mechanism and the
reachability state table as well as by keeping the Tunnel Server busy
determining the reachability state of the ever changing client nodes.
9.3. Implications of Direct Tunneling
In case direct tunneling in between end-hosts is provided by the
tunneling protocol, it will not (as described in Section 9.2.1) be
possibly for end-hosts to filter out received Protocol-41
encapsulated packets based on whether the IPv4 source is an address
belonging to a trusted Tunnel Server as such behavior evidently would
break direct tunneling.
As other end-hosts generally are non-trusted, direct tunneling may
thus open up for attacks against IPv6 ingress filtering.
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Detailed analysis of the validity of this threat will have to depend
on the particular zero-configuration solution.
10. Acknowledgments
Prior work by J. Mulahusic on the requirements for UE tunneling has
been considered in the initial stage of the work.
This work has benefited from input and comments provided by Fred
Templin in the initial phase of the work.
Thanks are due to Pekka Savola and Radhakrishnan Suryanarayanan for
many helpful comments and suggestions for improvements.
Corresponding work on assisted-tunneling, [5], has been an
inspiration for the Zero-Configuration Tunneling work.
The authors would like to acknowledge the European Commission support
in the co-funding of the Euro6IX project, where part of this work is
being developed.
11. Authors Addresses
Mario Morelli
Telecom Italia Lab.
Via Guglilmo Reiss Romoli, 274
I-10148 Turin,
Italy
Phone: +39 011 228 7790
Fax: +39 011 228 5069
Email: mario.morelli@tilab.com
Karen Egede Nielsen
Ericsson
Skanderborgvej 232
8260 Viby J
Denmark
Phone: + 45 89 38 51 00
Email: karen.e.nielsen@ericsson.com
Jordi Palet Martinez
Consulintel
San Jose Artesano, 1
Alcobendas - Madrid
E-28108 - Spain
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INTERNET-DRAFT Zeroconf Tunneling Goals October, 2004
Phone: +34 91 151 81 99
Fax: +34 91 151 81 98
EMail: jordi.palet@consulintel.es
Jonne Soininen
Nokia
Linnoitustie 6
02600 ESPOO
Finland
Phone: +358 7180 08000
EMail: jonne.soininen@nokia.com
Juha Wiljakka
Nokia
Visiokatu 3
33720 TAMPERE
Finland
Phone: +358 7180 48372
EMail: juha.wiljakka@nokia.com
12. Changes from draft-nielsen-v6ops-zeroconf-goals-01.txt
- Scope of document has been restricted to the 3GPP deployment
environment.
13. Informative References
[1] Nordmark, E., Basic Transition Mechanisms for IPv6 Hosts and
Routers, draft-ietf-v6ops-mech-v2-04.txt (work in progress),
July 2004.
[2] Lind, M., Scenarios and Analysis for Introducing IPv6 into ISP
Networks, draft-ietf-v6ops-isp-scenarios-analysis-03.txt (work
in progress), June 2004.
[3] Huitema, C., Evaluation of Transition Mechanisms for Unmanaged
Networks, draft-ietf-v6ops-unmaneval-03.txt (work in progress),
June 2004.
[4] Wiljakka, J., Analysis on IPv6 Transition in 3GPP Networks,
draft-ietf-v6ops-3gpp-analysis-10.txt (work in progress), May
2004.
[5] Durand, A., Requirements for assisted tunneling, draft-ietf-
v6ops-assisted-tunneling-requirements-00.txt (work in progress),
June 2004.
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INTERNET-DRAFT Zeroconf Tunneling Goals October, 2004
[6] Palet, J., Analysis of IPv6 Tunnel End-point Discovery
Mechanisms, draft-palet-v6ops-tun-auto-disc-01.txt (work in
progress), June 2004.
[7] Wasserman, M., Recommendations for IPv6 in 3GPP standards, RFC
3314.
[8] Loughney, J., IPv6 Node Requirements, draft-ietf-ipv6-node-
requirements-10.txt (work in progress), August 2004.
[9] IAB, IESG, IAB/IESG Recommendations on IPv6 Address Allocations
to Sites, RFC 3177.
[10] Savola, P., Security Considerations for 6to4, draft-ietf-v6ops-
6to4-security-04.txt (work in progress), July 2004.
[11] Nikander, P., IPv6 Neighbor Discovery (ND) Trust Models and
Threats, RFC 3756.
[12] Narten, T., Privacy Extensions for Stateless Address
Autoconfiguration in IPv6, RFC 3041.
[13] Narten, T., Neighbor Discovery for IP Version 6 (IPv6), RFC
2461.
[14] Jordi, P., draft-palet-v6ops-solution-tun-auto-disc-00 (work in
progress), September 2004.
Appendix A Out of Scope
[Editor's Note: This appendix can be removed in a future revision of
this document]
The following issues have been considered as being out of scope of
this work.
Mobile IPv6:
Support of Mobile IPv6 usage over the tunnel-link; here under
potential mechanisms required to support MIPv6 movement detection as
well as fast tunnel set-up for Mobile IPv6 session survivability.
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