V6ops WG V. Kuarsingh, Ed.
Internet-Draft Rogers Communications
Intended status: Informational Y. Lee
Expires: September 15, 2011 Comcast
O. Vautrin
Juniper Networks
March 14, 2011
6to4 Provider Managed Tunnels
draft-kuarsingh-v6ops-6to4-provider-managed-tunnel-02
Abstract
6to4 Provider Managed Tunnels (6to4-PMT) provide a framework which
can help manage 6to4 [RFC3056] tunnels operating an an anycast
[RFC3068] configuration. The 6to4-PMT framework is intended to serve
as an option to operators to help improve the experience of 6to4
operation when conditions of the network may provide sub-optimal
performance or break normal 6to4 operation. 6to4-PMT provides a
stable provider prefix and forwarding environment by utilizing
existing 6to4 Relays with an added function of IPv6 Prefix
Translation. This operation may be particularly important in NAT444
infrastructures where a customer endpoint may be assigned a non-
RFC1918 address thus breaking the return path for anycast [RFC3068]
based 6to4 operation.
Status of this Memo
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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. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. 6to4 Provider Managed Tunnels . . . . . . . . . . . . . . . . 5
3.1. 6to4 Provider Managed Tunnel Model . . . . . . . . . . . . 5
3.2. Traffic Flow . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Prefix Translation . . . . . . . . . . . . . . . . . . . . 6
3.4. Translation State . . . . . . . . . . . . . . . . . . . . 7
4. Deployment Considerations and Requirements . . . . . . . . . . 7
4.1. Customer Opt-out . . . . . . . . . . . . . . . . . . . . . 7
4.2. ISP Shared Space Considerations . . . . . . . . . . . . . 8
4.3. End to End Transparency . . . . . . . . . . . . . . . . . 8
4.4. Routing Requirements . . . . . . . . . . . . . . . . . . . 9
4.5. Relay Deployments . . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
6to4 [RFC3056] tunneling along with the anycast operation described
in [RFC3068] is widely deployed in modern Operating Systems and off
the shelf gateways sold throughout the retail and OEM channels.
Anycast [RFC3068] based 6to4 allows for tunneled IPv6 connectivity
through IPv4 clouds without explicit configuration of a relay
address. Since the overall system utilizes anycast forwarding in
both directions, flow paths are difficult to determine, tend to
follow separate paths in either direction, and often change based on
network conditions. The return path is normally uncontrolled by the
local operator and can contribute to poor performance for IPv6, and
can also act as a breakage point. Many of the challenges with 6to4
are described in [draft-carpenter-v6ops-6to4-teredo-advisor]. A
specific critical use case for problematic anycast 6to4 operation is
related to when the consumer endpoints are downstream from a
northbound NAT44 function when assigned non-RFC1918 addresses (common
future case in wireline networks and very common in wireless
networks).
Operators which are actively deploying IPv6 networks and operate
legacy IPv4 access environments may want to utilize the existing 6to4
behavior in customer site resident hardware and software as an
interim option to reach the IPv6 Internet in advance of being able to
offer full native IPv6. Operators may also need to address the
brokenness related to 6to4 operation originating from behind a
provider NAT function. 6to4-PMT offers a operator the opportunity to
utilize IPv6 Prefix Translation to enable deterministic and an
unbroken path to and from the Internet for IPv6 based traffic sourced
originally from these 6to4 customer endpoints.
6to4-PMT translates the prefix portion of the IPv6 address from the
6to4 generated prefix to a provider assigned prefix which is used to
represent the source. This translation will then provide a stable
forward and return path for the 6to4 traffic by allowing the existing
IPv6 routing and policy environment to control the traffic. 6to4-PMT
is primarily intended to be used in a stateless manner to maintain
many of the elements inherent in normal 6to4 operation.
Alternatively, 6to4-PMT can be used in a stateful translation mode
should the operator choose this option.
2. Motivation
Many operators endeavor to deploy IPv6 as soon as possible so as to
ensure uninterrupted connectivity to all Internet applications and
content through the IPv4 to IPv6 transition process. The IPv6
preparations within these organizations are often faced with both
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financial challenges and timing issues related to deploying IPv6 to
the network edge and related transition technologies. Many of the
new technologies addressing IPv4 to IPv6 transition will require the
replacement of the customer CPE to support technologies like 6RD
[RFC5969], Dual Stack Lite [draft-ietf-softwire-dual-stack-lite] and
Native Dual Stack.
Operators face a number of challenges related to home equipment
replacement. Operator initiated replacement of this equipment will
take time due to the nature of mass equipment refresh programs or may
require the consumer to replace their own gear. Replacing consumer
owned and operated equipment, compounded by the fact that there is
also a general unawareness of what IPv6 is, also adds the the
challenges faced by operators. It is also important to note that
6to4 is found in much of the equipment in networks today which do not
as of yet, or will not, support 6RD and/or Native Dual Stack.
Operators may still be motivated to provide a form of IPv6
connectivity to customers and would want to mitigate potential issues
related to IPv6-only deployments elsewhere on the Internet.
Operators also need to mitigate issues related to the fact that 6to4
operation often is on by default and may be subject to erroneous
behavior. The undesired behavior may be related to the use of non-
RFC1918 addresses on CPE equipment which operate behind large NATs,
or other conditions as described in a general advisory as laid out in
[draft-carpenter-v6ops-6to4-teredo-advisory].
6to4-PMT allows a operator to help mitigate such challenges by
leveraging the existing 6to4 deployment base, while maintaining
operator control of access to the IPv6 Internet. It is intended for
use when better options, such as 6RD or native IPv6, are not yet
viable. One of key objectives of 6to4-PMT is to also help reverse
the negative impacts of 6to4 in NAT444 environments. The 6to4-PMT
operation can also be used immediately and the default parameters are
often enough to allow it to operate in a 6to4-PMT environment. Once
native IPv6 is available to the endpoint, the 6to4-PMT operation is
no longer needed and will cease to be used based on correct address
selection behaviors in end hosts [RFC3484].
6to4-PMT thus helps operators remove the impact of 6to4 in NAT444
environments, deals with the fact that 6to4 is often on by default,
allows access to IPv6-only endpoints from IPv4-only addressed
equipment and provides relief from may challenges related to mis-
configuations in other networks. Due to the simple nature of 6to4-
PMT, it can also be implemented in a cost effective and simple manner
allowing operators to concentrate their energy on deploying native
IPv6.
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3. 6to4 Provider Managed Tunnels
3.1. 6to4 Provider Managed Tunnel Model
The 6to4 managed tunnel model behaves like a standard 6to4 service
between the customer IPv6 host or gateway and the 6ot4-PMT Relay
(within the provider domain). The 6to4-PMT Relay shares properties
with 6RD [RFC5969] by decapsulating and forwarding embedded IPv6
flows, within an IPv4 packet, to the IPv6 Internet. The model
provides an additional function which translates the source 6to4
prefix to a provider assigned prefix which is not found in 6RD
[RFC5969] or traditional 6to4 operation.
The 6to4-PMT Relay is intended to provide a stateless (or stateful)
mapping of the 6to4 prefix to a provider supplied prefix by mapping
the embedded IPv4 address in the 6to4 prefix to the provider prefix.
| 6to4-PMT Operation |
+-----+ 6to4 Tunnel +--------+ +------+ IPv6 +----+
| CPE |-------------|6to4 BR |--| PT66 |--------- |Host|
+-----+ IPv4 +--------+ +------+ Provider +----+
Network Prefix
Unified or Separate
Functions/Platforms
Figure 1: 6to4-PMT Functional Model
This mode of operation is seen as beneficial when compared to broken
6to4 paths and or environments where 6to4 operation may be functional
but highly degraded.
3.2. Traffic Flow
Traffic in the 6to4-PMT model is intended to be controlled by the
operator's IPv6 peering operations. Egress traffic is managed
through outgoing routing policy, and incoming traffic is influenced
by the operator assigned prefix advertisements.
The routing model is as predictable as native IPv6 traffic and legacy
IPv4 based traffic. Figure 2 provides a view of the routing topology
needed to support this relay environment. The diagram references
PrefixA as 2002::/16 and PrefixB as the example 2001:db8::/32.
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| 6to4 IPv4 Path | Native IPv6 Path |
----------- ----------- -------------
/ IPv4 Net \ / IPv6 Net \ / IPv6 Internet \
+------+ +--------+ +-------+ +---------+
| CPE | PrefixA |6to4-PMT| PrefixB |Peering| |IPv6 HOST|
+------+ +--------+ +-------+ +---------+
\ / \ / \ /
---------- ------------ --------------
IPv4 6to4 IPv6 Provider IPv6 Prefix
Anycast Prefix Advertisement
Figure 2: 6to4-PMT Flow Model
Traffic between two 6to4 enabled devices would use the IPv4 path for
communication according to RFC3056. 6to4-PMT is intended to be
deployed in conjunction with the 6to4 relay function in an attempt to
help simplify it's deployment. The model can also provide the
ability for an operator to forward both 6to4-PMT (translated) and
normal 6to4 flows (untranslated) simultaneously based on policy.
3.3. Prefix Translation
The IPv6 Prefix Translation is a key part of the system as a whole.
The 6to4-PMT framework is a combination of two concepts: 6to4
[RFC3056] and IPv6 Prefix Translation. IPv6 Prefix Translation has
some similarities to concepts discussed in [draft-mrw-nat66]. The
only change in this particular case is that the provider would build
specific rules on the translator to map the 6to4 prefix to an
appropriate provider assigned prefix.
The provider can use any prefix mapping strategy they so choose, but
the simpler the better. Simple direct bit mapping can be used such
as in Figure 2, or more advanced forms of translation can be used to
achieve higher address compression.
Figure 2 shows a 6to4 Prefix with a Subnet-ID of "0000" mapped to a
provider globally unique prefix (2001:db8::/32). With this simple
form of translation, there is support for only one Subnet-ID per
provider assigned prefix. In characterization of deployed OSs and
gateways, a subnet-id of "0000" is the most common default case.
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Pre-Relayed Packet [Provider Access Network Side]
0 16 32 48 64 80 96 112 128 Bits
| ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |
2002 : 0C98 : 2C01 : 0000 : xxxx : xxxx : xxxx : xxxx
| ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |
| | | | | |
---- ---- | | | |
| | | | | |
| ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |
2001 : 0db8 : 0c98 : 2c01 : xxxx : xxxx : xxxx : xxxx
| ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |
Post-Relayed Packet [Internet Side]
Figure 3: 6to4-PMT Prefix Mapping
Additional prefix compression techniques can be used such as those
described in [draft-tremblay-pt66ac]. These techniques would allow
for a more flexible implementation potentially supporting more
Subnet-IDs per provider prefix.
3.4. Translation State
It is preferred that the overall system use deterministic prefix
translation mappings such that stateless operation can be
implemented. This allows the provider to place N number of relays
within the network without the need to manage translation state.
If stateful operation is chosen, the operation would need to validate
state and routing requirements particular to that type of deployment.
The full body of considerations for this type of deployment are not
within this scope of this document.
4. Deployment Considerations and Requirements
4.1. Customer Opt-out
A provider enabling this function should provide a method to allow
customers to opt-out of such a service should the customer choose to
maintain normal 6to4 operation irrespective of degraded performance.
In cases where the customer is behind a NAT44 device (Provider CGN),
the customer would not be advised to opt-out and can also be assisted
to turn off 6to4.
Since the 6to4-PMT system is targeted at customers who are relatively
unaware of IPv6 and IPv4, and normally run network equipment with a
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default configuration, an opt-out strategy is recommended. This
method provides the 6to4-PMT operation for non-IPv6 savvy customers
whose equipment may turn on 6to4 automatically and allows savvy
customers to easily configure they way around the PMT function.
Capable customers can also disable anycast based 6to4 entirely and
use traditional 6to4 or other tunneling mechanisms if they are so
inclined. This is not considered the normal case, and most endpoints
with auto-6to4 operation will be subject to 6to4-PMT operation since
most users are unaware of it's existence. 6to4-PMT is targeted as an
option for stable IPv6 connectivity for average consumers.
4.2. ISP Shared Space Considerations
6to4-PMT operation can also be used to mitigate a known problem with
6to4 when ISP Shared Space
[draft-weil-shared-transition-space-request-01] or public but non-
routed IPv4 space is used. Public but un-routed address space would
cause many deployed OSs and network equipment to potentially auto-
enable 6to4 operation even without a valid return path (such as
behind NAT44 provider function). Operators' desire to use public but
un-routed IP space is considered highly likely based on points made
in [draft-weil-shared-transition-space-request] and in reports such
as [wide-tr-kato-as112-rep-01].
Such hosts, in normal cases, would send 6to4 traffic to the IPv6
Internet via the IPv4 anycast relay, which would in fact provide
broken IPv6 connectivity since the return path is based on an address
that is not routed or assigned to the source Network. The use of
6to4-PMT would help reverse these effects by translating the 6to4
prefix to a provided assigned prefix, masking this automatic and
undesired behavior.
4.3. End to End Transparency
6to4-PMT mode operation removes the traditional end to end
transparency of 6to4. Remote hosts would connect to a translated
IPv6 address versus the original 6to4 based prefix. This can be seen
as a disadvantage of the 6to4-PMT system. This lack of transparency
should also be contrasted with the normal operating state of 6to4
which provides uncontrolled and often high latency prone
connectivity. The lack of transparency is however a better form of
operation when extreme poor performance, broken IPv6 connectivity, or
no IPv6 connectivity is considered as the alternative.
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4.4. Routing Requirements
The provider would need to advertise the anycast IP range within the
IPv4 routing environment (service customers of interest) to attract
the 6to4 upstream traffic. To control this environment and make sure
all northbound traffic lands on a provider BR, the operator may
filter the anycast range from being advertised from customer
endpoints.
The provider would not be able to control route advertisements inside
the customer domain, but this use case is out of this document's
scope. It is likely in this case the end network/customer
understands IPv6 operation and is maintaining their own environment.
The provider would also likely want to advertise the 2002::/16 range
within their own network to help bridge within their own network
(Native IPv6 to 6to4-IPv6 based endpoint).
4.5. Relay Deployments
The 6to4-PMT function can be deployed onto existing 6to4 relays (if
desired) to help minimize network complexity. If used on Linux based
relays, 6to4-PMT can be a low cost add-on which can help align normal
6to4 and 6to4-PMT operation. The only additional considerations
beyond normal 6to4 relay operation would include the need to route
specific IPv6 address ranges to the IPv6 side interface to manage
return traffic.
5. IANA Considerations
No IANA considerations are defined at this time.
6. Security Considerations
6to4-PMT operation would be subject to the same security concerns as
normal 6to4 operation and with the operation of tunnels.
7. Acknowledgements
Thanks to the following people for their textual contributions and/or
guidance on 6to4 deployment considerations: Dan Wing, Wes George,
Scott Beuker, JF Tremblay, John Brzozowski, and Chris Donley
Additional thanks to the following for assisting with the coding and
testing of 6to4-PMT: Marc Blanchet, John Cianfarani, and Nik Lavorato
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8. References
8.1. Normative References
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, June 2001.
8.2. Informative References
[I-D.ietf-softwire-dual-stack-lite]
Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", draft-ietf-softwire-dual-stack-lite-07 (work
in progress), March 2011.
[I-D.mrw-nat66]
Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", draft-mrw-nat66-10 (work in progress),
March 2011.
[I-D.tremblay-pt66ac]
Tremblay, J. and S. Beuker, "Addressing bit compression
for stateless IPv6 prefix translation",
draft-tremblay-pt66ac-00 (work in progress),
November 2010.
[I-D.weil-shared-transition-space-request]
Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and
M. Azinger, "IANA Reserved IPv4 Prefix for Shared
Transition Space",
draft-weil-shared-transition-space-request-01 (work in
progress), November 2010.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification",
RFC 5969, August 2010.
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Authors' Addresses
Victor Kuarsingh (editor)
Rogers Communications
8200 Dixie Road
Brampton, Ontario L6T 0C1
Canada
Email: victor.kuarsingh@rci.rogers.com
URI: http://www.rogers.com
Yiu L. Lee
Comcast
One Comcast Center
Philadelphia, PA 19103
U.S.A.
Email: yiu_lee@cable.comcast.com
URI: http://www.comcast.com
Olivier Vautrin
Juniper Networks
1194 N Mathilda Avenue
Sunnyvale, CA 94089
U.S.A.
Email: olivier@juniper.net
URI: http://www.juniper.net
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