Internet Engineering Task Force A. Durand, Ed.
Internet-Draft Comcast
Intended status: Standards Track February 3, 2010
Expires: August 7, 2010
Dual-stack lite broadband deployments post IPv4 exhaustion
draft-ietf-softwire-dual-stack-lite-03
Abstract
This document revisits the dual-stack model and introduces the dual-
stack lite technology aimed at better aligning the costs and benefits
of deploying IPv6. Dual-stack lite enables a broadband service
provider to share IPv4 addresses among customers by combining two
well-known technologies: IP in IP (IPv4-in-IPv6) and NAT.
Status of this Memo
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements language . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Deployment scenarios . . . . . . . . . . . . . . . . . . . . . 5
4.1. Access model . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Home gateway . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Directly connected device . . . . . . . . . . . . . . . . 6
5. B4 element . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 7
5.3. Fragmentation and Reassembly . . . . . . . . . . . . . . . 7
5.4. AFTR discovery . . . . . . . . . . . . . . . . . . . . . . 7
5.5. DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.6. Interface initialization . . . . . . . . . . . . . . . . . 8
5.7. Well-known IPv4 address . . . . . . . . . . . . . . . . . 8
6. AFTR element . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 9
6.3. Fragmentation and Reassembly . . . . . . . . . . . . . . . 9
6.4. DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.5. Well-known IPv4 address . . . . . . . . . . . . . . . . . 10
6.6. Extended binding table . . . . . . . . . . . . . . . . . . 10
7. Network Considerations . . . . . . . . . . . . . . . . . . . . 10
7.1. Tunneling . . . . . . . . . . . . . . . . . . . . . . . . 10
7.2. VPN . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.3. Multicast considerations . . . . . . . . . . . . . . . . . 10
8. NAT considerations . . . . . . . . . . . . . . . . . . . . . . 10
8.1. NAT pool . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.2. NAT conformance . . . . . . . . . . . . . . . . . . . . . 10
8.3. ALG . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.4. Port allocation . . . . . . . . . . . . . . . . . . . . . 11
8.4.1. How many ports per customers? . . . . . . . . . . . . 11
8.4.2. Dynamic port assignment considerations . . . . . . . . 12
8.4.3. Subscriber controlled port assignment . . . . . . . . 12
8.5. Other considerations about sharing global IPv4
addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
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11. Security Considerations . . . . . . . . . . . . . . . . . . . 13
12. Author's Addresses . . . . . . . . . . . . . . . . . . . . . . 14
13. Appendix A: future DS-Lite extensions . . . . . . . . . . . . 15
13.1. Static port reservation . . . . . . . . . . . . . . . . . 15
13.1.1. Port forwarding model . . . . . . . . . . . . . . . . 16
13.1.2. A+P model . . . . . . . . . . . . . . . . . . . . . . 16
13.2. Dynamic port reservation . . . . . . . . . . . . . . . . . 16
13.2.1. UPnP . . . . . . . . . . . . . . . . . . . . . . . . . 16
13.2.2. NAT-PMP . . . . . . . . . . . . . . . . . . . . . . . 17
13.2.3. DHCPv6 . . . . . . . . . . . . . . . . . . . . . . . . 17
14. Appendix B: Examples . . . . . . . . . . . . . . . . . . . . . 17
14.1. Gateway based architecture . . . . . . . . . . . . . . . . 17
14.1.1. Example message flow . . . . . . . . . . . . . . . . . 20
14.1.2. Translation details . . . . . . . . . . . . . . . . . 24
14.2. Host based architecture . . . . . . . . . . . . . . . . . 25
14.2.1. Example message flow . . . . . . . . . . . . . . . . . 28
14.2.2. Translation details . . . . . . . . . . . . . . . . . 32
15. Appendix C: Deployment considerations . . . . . . . . . . . . 32
15.1. AFTR service distribution and horizontal scaling . . . . . 32
15.2. Horizontal scaling . . . . . . . . . . . . . . . . . . . . 33
15.3. High availability . . . . . . . . . . . . . . . . . . . . 33
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
16.1. Normative references . . . . . . . . . . . . . . . . . . . 33
16.2. Informative references . . . . . . . . . . . . . . . . . . 34
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 36
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1. Introduction
The common thinking for more than 10 years has been that the
transition to IPv6 will be based on the dual stack model and that
most things would be converted this way before we ran out of IPv4.
It has not happened. The IANA free pool of IPv4 addresses will be
depleted soon, well before any significant IPv6 deployment will have
occurred.
This document revisits the dual-stack model and introduces the dual-
stack lite technology aimed at better aligning the costs and benefits
of deploying IPv6. Dual-stack lite will provide the necessary bridge
between the two protocols, offering an evolution path of the Internet
post IANA IPv4 depletion.
Dual-stack lite enables a broadband service provider to share IPv4
addresses among customers by combining two well-known technologies:
IP in IP (IPv4-in-IPv6) and NAT.
This document makes a distinction between a dual-stack capable and a
dual-stack provisioned device. The former is a device that has code
that implements both IPv4 and IPv6, from the network layer to the
applications. The later is a similar device that has been
provisioned with both an IPv4 and an IPv6 address on its
interface(s). This document will also further refine this notion by
distinguishing between interfaces provisioned directly by the service
provider from those provisioned by the customer.
Pure IPv6-only devices (i.e. devices that do not include an IPv4
stack) are outside of the scope of this document.
2. Requirements language
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 RFC 2119 [RFC2119].
3. Terminology
The technology described in this document is known as dual-stack
lite. The abbreviation DS-Lite will be used along this text.
This document also introduces two new terms: the DS-Lite Basic
Bridging BroadBand element (B4) and the DS-Lite Address Family
Transition Router element (AFTR)
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4. Deployment scenarios
4.1. Access model
Instead of relying on a cascade of NATs, the dual-stack lite model is
built on IPv4-in-IPv6 tunnels to cross the network to reach a
carrier-grade IPv4-IPv4 NAT (the AFTR) where customers will share
IPv4 addresses. There are numbers of benefits to this approach:
o This technology decouples the deployment of IPv6 in the service
provider network (up to the customer premise equipment or CPE)
from the deployment of IPv6 in the global Internet and in customer
applications & devices.
o The management of the service provider access networks is
simplified by leveraging the large IPv6 address space.
Overlapping private IPv4 address spaces are not required to
support very large customer bases.
o As tunnels can terminate anywhere in the service provider network,
this architecture leads itself to horizontal scaling and provides
great flexibility to adapt to changing traffic load.
o Tunnels provide a direct connection between B4 and the AFTR. This
can be leverage to enable customers and their applications to
control how the NATing function of the AFTR is performed.
A key characteristic of this approach is that communications between
end-nodes stay within their address family. IPv6 sources only
communicate with IPv6 destinations, IPv4 sources only communicate
with IPv4 destinations. There is no protocol family translation
involved in this approach. This simplifies greatly the task of
applications that may carry literal IP addresses in their payload.
Using DS-Lite, they will not have to include special knowledge to
deal with possibly presence of a protocol family translator is in the
path...
4.2. Home gateway
This section describes home style networks characterized by the
presence of a home gateway provisioned only with IPv6 by the service
provider.
A DS-Lite home gateway is an IPv6 aware home gateway with a B4
Interface implemented in the WAN interface.
A DS-Lite home gateway SHOULD NOT operate a NAT function on a B4
interface, as the NAT function will be performed by the AFTR in the
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service provider's network. That will avoid accidentally operating
in a double NAT environment.
However, it SHOULD operate its own DHCP(v4) server handing out
[RFC1918] address space (e.g. 192.168.0.0/16) to hosts in the home.
It SHOULD advertise itself as the default IPv4 router to those home
hosts. It SHOULD also advertise itself as a DNS server in the DHCP
Option 6 (DNS Server). Additionally, it SHOULD operate a DNS proxy
to accept DNS IPv4 requests from home hosts and send them using IPv6
to the service provider DNS servers, as described in Section 5.5.
Note: if an IPv4 home hosts decides to use another IPv4 DNS server,
the DS-Lite home gateway will forward those DNS requests via the B4
interface, the same way it is forwarding any regular IPv4 packets.
IPv6 capable devices directly reach the IPv6 Internet. Packets
simply follow IPv6 routing, they do not go through the tunnel, and
are not subject to any translation. It is expected that most IPv6
capable devices will also be IPv4 capable and will simply be
configured with an IPv4 RFC1918 style address within the home network
and access the IPv4 Internet the same way as the legacy IPv4-only
devices within the home.
Pure IPv6-only devices (i.e. devices that do not include an IPv4
stack) are outside of the scope of this document.
4.3. Directly connected device
In broadband home networks, sometime devices are directly connected
to the broadband service provider. They are connected straight to a
modem, without home gateway. This scenario is identical to wireless
devices directly connected over the air interface to their provider.
Under this scenario, the customer device is a dual-stack capable host
that is only provisioned by the service provider only with IPv6. The
device itself acts as a B4 element and the IPv4 service is provided
by an IPv4-in-IPv6 tunnel, just as in the home gateway case. That
device can run any combinations of IPv4 and/or IPv6 applications.
A directly connected DS-Lite device SHOULD send its DNS requests over
IPv6 to the IPv6 DNS server it has been configured to use.
Similarly to the previous sections, IPv6 packets follow IPv6 routing,
they do not go through the tunnel, and are not subject to any
translation.
The support of IPv4-only devices and IPv6-only devices in this
scenario is out of scope for this document.
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5. B4 element
5.1. Definition
The B4 element is a function implemented on a dual-stack capable
node, either a directly connected device or a home gateway, that
creates a tunnel to an AFTR.
5.2. Encapsulation
The tunnel is a multi-point to point IPv4-in-IPv6 tunnel ending on a
service provider AFTR.
See section 7.1 for additional tunneling considerations.
Note: at this point, DS-Lite only defines IPv4-in-IPv6 tunnels,
however other types of encapsulation could be defined in the future.
5.3. Fragmentation and Reassembly
Using an encapsulation (IPv4-in-IPv6 or anything else) to carry IPv4
traffic over IPv6 will reduce the effective MTU of the datagram.
Unfortunately, path MTU discovery [RFC1191] is not a reliable method
to deal with this problem.
A solution to deal with this problem is for the service provider to
increase the MTU size of all the links between the B4 element and the
AFTR elements by at least 40 bytes to accommodate both the IPv6
encapsulation header and the IPv4 datagram without fragmenting the
IPv6 packet.
However,as not all service provider will be able to increase their
link MTU, the B4 element MUST perform fragmentation and reassembly if
the outgoing link MTU cannot accommodate for the extra IPv6 header.
Fragmentation MUST happen after the encapsulation on the IPv6 packet.
Reassembly MUST happen before the decapsulation of the IPv6 header.
Detailed procedure has been specified in [RFC2473] Section 7.2.
5.4. AFTR discovery
In order to configure the IPv4-in-IPv6 tunnel, the B4 element needs
the IPv6 address of the AFTR element. This IPv6 address can be
configured using a variety of methods, ranging from an out-of-band
mechanism, manual configuration or a variety of DHCPv6 options.
In order to guarantee interoperability, a B4 element SHOULD implement
the DHCPv6 option defined in
[I-D.ietf-softwire-ds-lite-tunnel-option].
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5.5. DNS
A B4 element is only configured from the service provider with IPv6.
As such, it can only learn the address of a DNS recursive server
through DHCPv6 (or other similar method over IPv6). As DHCPv6 only
defines an option to get the IPv6 address of such a DNS recursive
server, the B4 element cannot easily discover the IPv4 address of
such a recursive DNS server, and as such will have to perform all DNS
resolution over IPv6.
The B4 element can pass this IPv6 address to downstream IPv6 nodes,
but not to downstream IPv4 nodes. As such, the B4 element MUST
implement a DNS proxy, following the recommendations of [RFC5625].
5.6. Interface initialization
Initialization of the interface including a B4 element is out-of-
scope in this specification.
5.7. Well-known IPv4 address
Any locally unique IPv4 address could be configured on the IPv4-in-
IPv6 tunnel to represent the B4 element. Configuring such an address
is often necessary when the B4 element is sourcing IPv4 datagrams
directly over the tunnel. In order to avoid conflicts with any other
address, IANA has defined a well-known range, 192.0.0.0/29.
192.0.0.0 is the reserved subnet address. 192.0.0.1 is reserved for
the AFTR element. The B4 element SHOULD use any other addresses
within the 192.0.0.0/29 range.
Note: a range of addresses has been reserved for this purpose. The
intend is to accommodate for nodes implementing several B4
elements... The mechanisms to decide which of those addresses to use
on a B4 element is implementation dependant and out of scope for this
document.
6. AFTR element
6.1. Definition
An AFTR element is the combination of an IPv4-in-IPv6 tunnel end-
point and an IPv4-IPv4 NAT implemented on the same node.
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6.2. Encapsulation
The tunnel is a point-to-multipoint IPv4-in-IPv6 tunnel ending at the
service provider subscribers B4 elements.
See section 7.1 for additional tunneling considerations.
Note: at this point, DS-Lite only defines IPv4-in-IPv6 tunnels,
however other types of encapsulation could be defined in the future.
6.3. Fragmentation and Reassembly
As noted previously, fragmentation and reassembly need to be taken
care of by the tunnel end-points. As such, the AFTR MUST perform
fragmentation and reassembly if the underlying link MTU cannot
accommodate for the extra IPv6 header of the tunnel. Fragmentation
MUST happen after the encapsulation on the IPv6 packet. Reassembly
MUST happen before the decapsulation of the IPv6 header. Detailed
procedure has been specified in [RFC2473] Section 7.2.
Fragmentation at the Tunnel Entry-Point is a light-weighted
operation. In contrast, reassembly at the Tunnel Exit-Point can be
expensive. When the Tunnel Exit-Point receives the first fragmented
packet, it must wait for the second fragmented packet to arrive in
order to reassemble the two fragmented IPv6 packets for
decapsulation. This requires the Tunnel Exit-Point to buffer and
keep track of fragmented packets. Consider that the AFTR is the
Tunnel Exit-Point for many tunnels. If many clients simultaneously
source large number of fragmented packets to the AFTR, this will
demand the AFTR to buffer and consume enormous resources to keep
track of the flows. This reassembly process will significantly
impact the AFTR performance. However, this impact only happens when
many clients simultaneously source large IPv4 packets. Since we
believe that majority of the clients will receive large IPv4 packets
(such as watching video streams) instead of sourcing large IPv4
packets (such as sourcing video streams), so reassembly is only a
fraction of the overall AFTR's workload.
Other methods to avoid fragmentation, such as rewriting the TCP MSS
option or using technologies such as Subnetwork Encapsulation and
Adaptation Layer defined in [I-D.templin-seal] are out of scope for
this document.
6.4. DNS
As noted previously, DS-Lite node implementing a B4 elements will
perform DNS resolution over IPv6. As such, very few, if any, DNS
traffic will flow through the AFTR element.
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6.5. Well-known IPv4 address
The AFTR MAY use the well-know IPv4 address 192.0.0.1 reserved by
IANA to configure the IPv4-in-IPv6 tunnel. That address can then be
used to report ICMP problems and will appear in traceroute outputs.
6.6. Extended binding table
The NAT binding table of the AFTR element is extended to include the
source IPv6 address of the incoming packets. This IPv6 address will
disambiguate between the overlapping IPv4 address space of the
service provider customers.
By doing a reverse look-up in the extended IPv4 NAT binding table,
the AFTR knows how to reconstruct the IPv6 encapsulation when the
packets comes back from the Internet. That way, there is no need to
keep a static configuration for each tunnel.
7. Network Considerations
7.1. Tunneling
Tunneling MUST be done in accordance to [RFC2473] and [RFC4213].
Traffic classes ([RFC2474]) from the IPv4 headers SHOULD be carried
over to the IPv6 headers and vice versa.
7.2. VPN
The combination of the dual-stack lite technology with either IPv4
VPNs or IPv6 VPNs is out of scope for this document.
7.3. Multicast considerations
Multicast is out-of-scope in this document.
8. NAT considerations
8.1. NAT pool
It is expected that AFTRs will operate distinct, non overlapping NAT
pools. However, those NAT pools do not have to be continuous.
8.2. NAT conformance
A dual-stack lite AFTR SHOULD implement behavior conforming to the
best current practice, currently documented in [RFC4787], [RFC5382]
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and [RFC5508]. Other requirements for AFTRs can be found in
[I-D.nishitani-cgn].
8.3. ALG
The AFTR should only perform a minimum number of ALG for the classic
applications such as FTP, RTSP/RTP, IPsec and PPTP VPN pass-through
and enable the users to use their own ALG on statically or
dynamically reserved port instead.
8.4. Port allocation
8.4.1. How many ports per customers?
Because IPv4 addresses will be shared among customers and potentially
a large address space reduction factor may be applied, in average,
only a limited number N of TCP or UDP port numbers will be available
per customer. This means that applications opening a very large
number of TCP ports may have a harder time to work. For example, it
has been reported that a very well know web site was using AJAX
techniques and was opening up to 69 TCP ports per web page. If we
make the hypothesis of an address space reduction of a factor 100
(one IPv4 address per 100 customers), and 65k ports per IPv4
addresses available, that makes an average of N = 650 ports available
simultaneously to be shared among the various devices behind the
dual-stack lite tunnel end-point.
There is an important operational difference if those N ports are
pre-allocated in a cookie-cutter fashion versus allocated on demand
by incoming connections. This is a difference between an average of
N ports and a maximum of N ports. Several service providers have
reported an average number of connections per customer in the single
digit. At the opposite end, thousands or tens of thousands of ports
could be use in a peak by any single customer browsing a number of
AJAX/Web 2.0 sites.
As such, service provider allocating a fixed number of ports per user
should dimension the system with a minimum of N = several thousands
of ports for every user. This would bring the address space
reduction ratio to a single digit. Service providers using a smaller
number of ports per user (N in the hundreds) should expect customers
applications to break in a more or less random way over time.
In order to achieve higher address space reduction ratios, it is
recommended that service provider do not use this cookie-cutter
approach, and, on the contrary, allocate ports as dynamically as
possible, just like on a regular NAT. With an average number of
connections per customers in the single digit, having an address
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space reduction of a factor 100 is realistic. However, service
providers should exercise caution and make sure their pool of port
numbers does not go too low. The actual maximum address space
reduction factor is unknown at this time.
8.4.2. Dynamic port assignment considerations
When dynamic port assignment is used to maximize the number of
subscriber sharing each AFTR global IPv4 address, the should
implement checks to avoid DOS attack through exhaustion of available
ports. It should also avoid mapping any one subscriber's "flows"
across more than one global IPv4 address.
8.4.3. Subscriber controlled port assignment
Dynamic port assignment precludes inbound access to subscriber
servers, just as in a home gateway NAT. Inbound access to subscriber
servers can be provided through pre-assigned and/or reserved port
mappings in the AFTR. Specifying the mechanisms for managing and
signaling these reserved port mappings is out of scope for this
document, however some techniques are mentioned in appendix A as
examples.
8.5. Other considerations about sharing global IPv4 addresses
More considerations on sharing the port space of IPv4 addresses can
be found in [I-D.ford-shared-addressing-issues].
9. Acknowledgements
The authors would like to acknowledge the role of Mark Townsley for
his input on the overall architecture of this technology by pointing
this work in the direction of [I-D.droms-softwires-snat]. Note that
this document results from a merging of [I-D.durand-dual-stack-lite]
and [I-D.droms-softwires-snat].Also to be acknowledged are the many
discussions with a number of people including Shin Miyakawa,
Katsuyasu Toyama, Akihide Hiura, Takashi Uematsu, Tetsutaro Hara,
Yasunori Matsubayashi, Ichiro Mizukoshi. The author would also like
to thank David Ward, Jari Arkko, Thomas Narten and Geoff Huston for
their constructive feedbacks. Special thanks go to Dave Thaler and
Dan Wing for their reviews and comments.
10. IANA Considerations
This draft request IANA to allocate a well know IPv4 192.0.0.0/29
network prefix. That range is used to number the dual-stack lite
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interfaces. Reserving a /29 allows for 6 possible interfaces on a
multi-home node. The IPv4 address 192.0.0.1 is reserved as the IPv4
address of the default router for such dual-stack lite hosts.
11. Security Considerations
Security issues associated with NAT have long been documented. See
[RFC2663] and [RFC2993].
However, moving the NAT functionality from the home gateway to the
core of the service provider network and sharing IPv4 addresses among
customers create additional requirements when logging data for abuse
usage. With any architecture where an IPv4 address does not uniquely
represent an end host, IPv4 addresses and a timestamps are no longer
sufficient to identify a particular broadband customer. Additional
information such as transport protocol information will be required
for that purpose. For example, we suggest to log the transport port
number for TCP and UDP connections.
The AFTR performs translation functions for interior IPv4 hosts at
RFC 1918 addresses or at the IANA reserved address range (TBA by
IANA). If the interior host is properly using the authorized IPv4
address with the authorized transport protocol port range such as A+P
semantic for the tunnel, the AFTR can simply forward without
translation to permit the authorized address and port range to
function properly. All packets with unauthorized interior IPv4
addresses or with authorized interior IPv4 address but unauthorized
port range MUST NOT be forwarded by the AFTR. This prevents rogue
devices from launching denial of service attacks using unauthorized
public IPv4 addresses in the IPv4 source header field or unauthorized
transport port range in the IPv4 transport header field. For
example, rogue devices could bombard a public web server by launching
TCP SYN ACK attack. The victim will receive TCP SYN from random IPv4
source addresses at a rapid rate and deny TCP services to legitimate
users.
With IPv4 addresses shared by multiple users, ports become a critical
resource. As such, some mechanisms need to be put in place by an
AFTR to limit port usage, either by rate-limiting new connections or
putting a hard limit on the maximum number of port usable by single
user. If this number is high enough, it should not interfere with
normal usage and still provide reasonable protection of the shared
pool. More considerations on ports allocation and port exhaustion
can be found in section 8.4.
More considerations on sharing IPv4 addresses can be found in
"I-D.ford-shared-addressing-issues".
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AFTRs should support ways to limit service to registered customers.
If strict IPv6 ingress filtering is deployed in the broadband network
to prevent IPv6 address spoofing and dual-stack lite service is
restricted to those customers, then tunnels terminating at the AFTR
and coming from registered customer IPv6 addresses cannot be spoofed.
Thus a simple access control list on the tunnel transport source
address is all what is required to accept traffic on the southbound
interface of an AFTR.
If IPv6 address spoofing prevention is not in place, the AFTR should
perform further sanity checks on the IPv6 address of incoming IPv6
packets. For example, it should check if the address has really been
allocated to an authorized customer.
12. Author's Addresses
This document is the result of the work of the following authors:
Alain Durand
Comcast
1, Comcast center
Philadelphia, PA 19103
USA
Email: alain_durand@cable.comcast.com
Ralph Droms
Cisco
1414 Massachusetts Avenue
Boxborough, MA 01714
USA
Phone: +1 978.936.1674
Email: rdroms@cisco.com
Brian Haberman
Johns Hopkins University Applied Physics Lab
11100 Johns Hopkins Road
Laurel, MD 20723-6099
USA
Phone: +1 443 778 1319
Email: brian@innovationslab.net
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James Woodyatt
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
USA
Email: jhw@apple.com
Yiu Lee
Comcast
1, Comcast center
Philadelphia, PA 19103
USA
Email: yiu_lee@cable.comcast.com
Randy Bush
Internet Initiative Japan
5147 Crystal Springs
Bainbridge Island, Washington 98110
USA
Phone: +1 206 780 0431 x1
Email: randy@psg.com
13. Appendix A: future DS-Lite extensions
Techniques discussed bellow are not part of the core dual-stack lite
specification and will be developed in separate documents. They are
only listed here as examples.
Application expecting incoming connections, such a peer-to-peer ones,
have become popular. Those applications use a very limited number of
ports, usually a single one. Making sure those applications keep
working in a dual-stack lite environment is important. Similarly,
there is a growing list of applications that require some king of ALG
to work through a NAT. Service provider AFTRs should not to be in
the way of the deployment of such applications. As such, there is a
legitimate need to leave certain ports under the control of the end
user. This argue for an hybrid environment, where most ports are
dynamically managed by the AFTR in a shared pool and a limited number
are dedicated per users and controlled by them.
13.1. Static port reservation
A service provider can reserve a static number of ports per user.
Note: those could be TCP and/or UDP ports. The simplest model to
allow users to control the associated NAT bindings is to offer a web
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interface (for example as part of the service provider portal) where,
once authenticated, a user can configure each dedicated external IPv4
address/port binding on the AFTR either using the port forwarding
semantic or the A+P semantic.
Note: The exact number of ports reserved per user is left at the
discretion of the service provider.
13.1.1. Port forwarding model
In this model, the subscriber directs the AFTR to rewrite the
destination address in those incoming packets to a private IPv4
address within the home network. For obvious security reasons,
redirection to global IPv4 address should not be authorized. Note:
this behavior is very similar to the port forwarding function found
in most home gateways.
13.1.2. A+P model
The subscriber directs the AFTR to forward incoming traffic on a
given address/port to the dual-stack lite home gateway, and let this
device deal with it. This required support for A+P [I-D.ymbk-aplusp]
semantic on both the AFTR and on the home gateway.
In particular, an A+P aware home router can locally NAT A+P packets
to and from internal hosts. Alternatively, it can forward directly
the traffic to those hosts if they are configured, for example, with
A+P secondary address and ports.
An AFTR forwards packets in the A+P range directly to and from the
tunnels without NAT.
13.2. Dynamic port reservation
13.2.1. UPnP
A B4 element can act as a UPnP relay, forwarding UPnP messages over
the tunnel to the AFTR. This may work in some cases, but not all the
time. Some applications insist on running on a well-known port
number (or port range) using UPnP to request the NAT to reserve that
port. Those ports may or may not be available; they could be used by
another customer. Using UPnP, a NAT box does not have any way to
redirect such applications to use another port, the only option is to
deny the request. Those applications typically then cycle through a
small range of ports (typically 10 or so) until they abort. The
likelihood of those ports being all already in use by other users is
an inverse function of the address space reduction, ie, how many
users are sharing the same address.
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Note: the UPnP forum has been reported to address this issue in an
upcoming version of the IGD profile.
13.2.2. NAT-PMP
NAT-PMP [I-D.cheshire-nat-pmp] offers a better semantic, by enabling
the NAT to redirect the application to use another unallocated port.
A B4 element could proxy the NAT-PMP messages to the AFTR through the
tunnel.
13.2.3. DHCPv6
If more ports need to be reserved outside of that static dedicated
range, a DHCPv6 option such as
[I-D.bajko-v6ops-port-restricted-ipaddr-assign] may also be an
interesting approach. This may be limited to the A+P semantic
mentioned above, as there might not be a way to explicitly control
the port forwarding semantic. Also, there are concerns that this
would lead to a cookie cutter distribution of ports per customers,
dramatically reducing the ratio of customer per IPv4 address.
14. Appendix B: Examples
14.1. Gateway based architecture
This architecture is targeted at residential broadband deployments
but can be adapted easily to other types of deployment where the
installed base of IPv4-only device is important.
Consider a scenario where a Dual-Stack lite home gateway is
provisioned only with IPv6 in the WAN port, no IPv4. The home
gateway acts as an IPv4 DCHP server for the LAN network (wireline and
wireless) handing out RFC1918 addresses. In addition, the home
gateway may support IPv6 Auto-Configuration and/or DHCPv6 server for
the LAN network. When an IPv4-only device connects to the home
gateway, the gateway will hand it out a RFC1918 address. When a
dual-stack capable device connects to the home gateway, the gateway
will hand out a RFC1918 address and a global IPv6 address to the
device. Besides, the home gateway will create an IPv4-in-IPv6
softwire tunnel [RFC5571]to an AFTR that resides in the service
provider network.
When the device accesses IPv6 service, it will send the IPv6 datagram
to the home gateway natively. The home gateway will route the
traffic upstream to the default gateway.
When the device accesses IPv4 service, it will source the IPv4
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datagram with the RFC1918 address and send the IPv4 datagram to the
home gateway. The home gateway will encapsulate the IPv4 datagram
inside the IPv4-in-IPv6 softwire tunnel and forward the IPv6 datagram
to the AFTR. This contrasts what the home gateways normally do today
which will NAT the RFC1918 address to the public IPv4 address and
route the datagram upstream. When the AFTR receives the IPv6
datagram, it will decapsulate the IPv6 header and perform an IPv4-to-
IPv4 NAT on the source address.
As illustrated in Figure 1, this dual-stack lite deployment model
consists of three components: the dual-stack lite home router with a
B4 element, the AFTR and a softwire between the B4 element acting as
softwire initiator (SI) [RFC5571] in the dual-stack lite home router
and the softwire concentrator (SC) [RFC5571] in the AFTR. The AFTR
performs IPv4-IPv4 NAT translations to multiplex multiple subscribers
through a pool of global IPv4 address. Overlapping address spaces
used by subscribers are disambiguated through the identification of
tunnel endpoints.
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+-----------+
| Host |
+-----+-----+
|10.0.0.1
|
|
|10.0.0.2
+---------|---------+
| | |
| Home router |
|+--------+--------+|
|| B4 ||
|+--------+--------+|
+--------|||--------+
|||2001:0:0:1::1
|||
|||<-IPv4-in-IPv6 softwire
|||
-------|||-------
/ ||| \
| ISP core network |
\ ||| /
-------|||-------
|||
|||2001:0:0:2::1
+--------|||--------+
| AFTR |
|+--------+--------+|
|| Concentrator ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
|129.0.0.1
|
--------|--------
/ | \
| Internet |
\ | /
--------|--------
|
|128.0.0.1
+-----+-----+
| IPv4 Host |
+-----------+
Figure 1: gateway-based architecture
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Notes:
o The dual-stack lite home router is not required to be on the same
link as the host
o The dual-stack lite home router could be replaced by a dual-stack
lite router in the service provider network
The resulting solution accepts an IPv4 datagram that is translated
into an IPv4-in-IPv6 softwire datagram for transmission across the
softwire. At the corresponding endpoint, the IPv4 datagram is
decapsulated, and the translated IPv4 address is inserted based on a
translation from the softwire.
14.1.1. Example message flow
In the example shown in Figure 2, the translation tables in the AFTR
is configured to forward between IP/TCP (10.0.0.1/10000) and IP/TCP
(129.0.0.1/5000). That is, a datagram received by the dual-stack
lite home router from the host at address 10.0.0.1, using TCP DST
port 10000 will be translated a datagram with IP SRC address
129.0.0.1 and TCP SRC port 5000 in the Internet.
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+-----------+
| Host |
+-----+-----+
| |10.0.0.1
IPv4 datagram 1 | |
| |
v |10.0.0.2
+---------|---------+
| | |
| home router |
|+--------+--------+|
|| B4 ||
|+--------+--------+|
+--------|||--------+
| |||2001:0:0:1::1
IPv6 datagram 2| |||
| |||<-IPv4-in-IPv6 softwire
| |||
-----|-|||-------
/ | ||| \
| ISP core network |
\ | ||| /
-----|-|||-------
| |||
| |||2001:0:0:2::1
+------|-|||--------+
| | AFTR |
| v ||| |
|+--------+--------+|
|| Concentrartor ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
| |129.0.0.1
IPv4 datagram 3 | |
| |
-----|--|--------
/ | | \
| Internet |
\ | | /
-----|--|--------
| |
v |128.0.0.1
+-----+-----+
| IPv4 Host |
+-----------+
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Figure 2: Outbound Datagram
+-----------------+--------------+---------------+
| Datagram | Header field | Contents |
+-----------------+--------------+---------------+
| IPv4 datagram 1 | IPv4 Dst | 128.0.0.1 |
| | IPv4 Src | 10.0.0.1 |
| | TCP Dst | 80 |
| | TCP Src | 10000 |
| --------------- | ------------ | ------------- |
| IPv6 Datagram 2 | IPv6 Dst | 2001:0:0:2::1 |
| | IPv6 Src | 2001:0:0:1::1 |
| | IPv4 Dst | 128.0.0.1 |
| | IPv4 Src | 10.0.0.1 |
| | TCP Dst | 80 |
| | TCP Src | 10000 |
| --------------- | ------------ | ------------- |
| IPv4 datagram 3 | IPv4 Dst | 128.0.0.1 |
| | IPv4 Src | 129.0.0.1 |
| | TCP Dst | 80 |
| | TCP Src | 5000 |
+-----------------+--------------+---------------+
Datagram header contents
When datagram 1 is received by the dual-stack lite home router, the
B4 function encapsulates the datagram in datagram 2 and forwards it
to the dual-stack lite carrier-grade NAT over the softwire.
When it receives datagram 2, the tunnel concentrator in the AFTR
hands the IPv4 datagram to the NAT, which determines from its
translation table that the datagram received on Softwire_1 with TCP
SRC port 10000 should be translated to datagram 3 with IP SRC address
129.0.0.1 and TCP SRC port 5000.
Figure 3 shows an inbound message received at the AFTR. When the NAT
function in the AFTR receives datagram 1, it looks up the IP/TCP DST
in its translation table. In the example in Figure 3, the NAT
translates the TCP DST port to 10000, sets the IP DST address to
10.0.0.1 and hands the datagram to the SC for transmission over
Softwire_1. The B4 in the home router decapsulates IPv4 datagram
from the inbound softwire datagram, and forwards it to the host.
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+-----------+
| Host |
+-----+-----+
^ |10.0.0.1
IPv4 datagram 3 | |
| |
| |10.0.0.2
+---------|---------+
| +-+-+ |
| home router |
|+--------+--------+|
|| B4 ||
|+--------+--------+|
+--------|||--------+
^ |||2001:0:0:1::1
IPv6 datagram 2 | |||
| |||<-IPv4-in-IPv6 softwire
| |||
-----|-|||-------
/ | ||| \
| ISP core network |
\ | ||| /
-----|-|||-------
| |||
| |||2001:0:0:2::1
+------|-|||--------+
| AFTR |
|+--------+--------+|
|| Concentrator ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
^ |129.0.0.1
IPv4 datagram 1 | |
| |
-----|--|--------
/ | | \
| Internet |
\ | | /
-----|--|--------
| |
| |128.0.0.1
+-----+-----+
| IPv4 Host |
+-----------+
Figure 3: Inbound Datagram
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+-----------------+--------------+---------------+
| Datagram | Header field | Contents |
+-----------------+--------------+---------------+
| IPv4 datagram 1 | IPv4 Dst | 129.0.0.1 |
| | IPv4 Src | 128.0.0.1 |
| | TCP Dst | 5000 |
| | TCP Src | 80 |
| --------------- | ------------ | ------------- |
| IPv6 Datagram 2 | IPv6 Dst | 2001:0:0:1::1 |
| | IPv6 Src | 2001:0:0:2::1 |
| | IPv4 Dst | 10.0.0.1 |
| | IP Src | 128.0.0.1 |
| | TCP Dst | 10000 |
| | TCP Src | 80 |
| --------------- | ------------ | ------------- |
| IPv4 datagram 3 | IPv4 Dst | 10.0.0.1 |
| | IPv4 Src | 128.0.0.1 |
| | TCP Dst | 10000 |
| | TCP Src | 80 |
+-----------------+--------------+---------------+
Datagram header contents
14.1.2. Translation details
The AFTR has a NAT that translates between softwire/port pairs and
IPv4-address/port pairs. The same translation is applied to IPv4
datagrams received on the device's external interface and from the
softwire endpoint in the device.
In Figure 2, the translator network interface in the AFTR is on the
Internet, and the softwire interface connects to the dual-stack lite
home router. The AFTR translator is configured as follows:
Network interface: Translate IPv4 destination address and TCP
destination port to the softwire identifier and TCP destination
port
Softwire interface: Translate softwire identifier and TCP source
port to IPv4 source address and TCP source port
Here is how the translation in Figure 3 works:
o Datagram 1 is received on the AFTR translator network interface.
The translator looks up the IPv4-address/port pair in its
translator table, rewrites the IPv4 destination address to
10.0.0.1 and the TCP source port to 10000, and hands the datagram
to the SE to be forwarded over the softwire.
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o The IPv4 datagram is received on the dual-stack lite home router
B4. The B4 function extracts the IPv4 datagram and the dual-stack
lite home router forwards datagram 3 to the host.
+----------------------------------+--------------------+
| Softwire-Id/IPv4/Prot/Port | IPv4/Prot/Port |
+----------------------------------+--------------------+
| 2001:0:0:1::1/10.0.0.1/TCP/10000 | 129.0.0.1/TCP/5000 |
+----------------------------------+--------------------+
Dual-Stack lite carrier-grade NAT translation table
The Softwire-Id is the IPv6 address assigned to the Dual-Stack lite
home gateway. Hosts behind the same Dual-Stack lite home router have
the same Softwire-Id. The source IPv4 is the RFC1918 addressed
assigned by the Dual-Stack home router which is unique to each host
behind the home gateway. The AFTR would receive packets sourced from
different IPv4 addresses in the same softwire tunnel. The AFTR
combines the Softwire-Id and IPv4 address/Port [Softwire-Id, IPv4+
Port] to uniquely identify the host behind the same Dual-Stack lite
home router.
14.2. Host based architecture
This architecture is targeted at new, large scale deployments of
dual-stack capable devices implementing a dual-stack lite interface.
Consider a scenario where a Dual-Stack lite host device is directly
connected to the service provider network. The host device is dual-
stack capable but only provisioned an IPv6 global address. Besides,
the host device will pre-configure a well-known IPv4 non-routable
address (see IANA section). This well-known IPv4 non-routable
address is similar to the 127.0.0.1 loopback address. Every host
device implemented Dual-Stack lite will pre-configure the same
address. This address will be used to source the IPv4 datagram when
the device accesses IPv4 services. Besides, the host device will
create an IPv4-in-IPv6 softwire tunnel to an AFTR. The Carrier Grade
NAT will reside in the service provider network.
When the device accesses IPv6 service, the device will send the IPv6
datagram natively to the default gateway.
When the device accesses IPv4 service, it will source the IPv4
datagram with the well-known non-routable IPv4 address. Then, the
host device will encapsulate the IPv4 datagram inside the IPv4-in-
IPv6 softwire tunnel and send the IPv6 datagram to the AFTR. When
the AFTR receives the IPv6 datagram, it will decapsulate the IPv6
header and perform IPv4-to-IPv4 NAT on the source address.
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This scenario works on both wireline and wireless networks. A
typical wireless device will connect directly to the service provider
without home gateway in between.
As illustrated in Figure 4, this dual-stack lite deployment model
consists of three components: the dual-stack lite host, the AFTR and
a softwire between the softwire initiator B4 in the host and the
softwire concentrator in the AFTR. The dual-stack lite host is
assumed to have IPv6 service and can exchange IPv6 traffic with the
AFTR.
The AFTR performs IPv4-IPv4 NAT translations to multiplex multiple
subscribers through a pool of global IPv4 address. Overlapping IPv4
address spaces used by the dual-stack lite hosts are disambiguated
through the identification of tunnel endpoints.
In this situation, the dual-stack lite host configures the IPv4
address 192.0.0.2 out of the well-known range 192.0.0.0/29 (defined
by IANA) on its B4 interface. It also configure the first non-
reserved IPv4 address of the reserved range, 192.0.0.1 as the address
of its default gateway.
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+-------------------+
| |
| Host 192.0.0.2 |
|+--------+--------+|
|| B4 ||
|+--------+--------+|
+--------|||--------+
|||2001:0:0:1::1
|||
|||<-IPv4-in-IPv6 softwire
|||
-------|||-------
/ ||| \
| ISP core network |
\ ||| /
-------|||-------
|||
|||2001:0:0:2::1
+--------|||--------+
| AFTR |
|+--------+--------+|
|| Concentrator ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
|129.0.0.1
|
--------|--------
/ | \
| Internet |
\ | /
--------|--------
|
|128.0.0.1
+-----+-----+
| IPv4 Host |
+-----------+
Figure 4: host-based architecture
The resulting solution accepts an IPv4 datagram that is translated
into an IPv4-in-IPv6 softwire datagram for transmission across the
softwire. At the corresponding endpoint, the IPv4 datagram is
decapsulated, and the translated IPv4 address is inserted based on a
translation from the softwire.
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14.2.1. Example message flow
In the example shown in Figure 5, the translation tables in the AFTR
is configured to forward between IP/TCP (a.b.c.d/10000) and IP/TCP
(129.0.0.1/5000). That is, a datagram received from the host at
address 192.0.0.2, using TCP DST port 10000 will be translated a
datagram with IP SRC address 129.0.0.1 and TCP SRC port 5000 in the
Internet.
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+-------------------+
| |
|Host 192.0.0.2 |
|+--------+--------+|
|| B4 ||
|+--------+--------+|
+--------|||--------+
| |||2001:0:0:1::1
IPv6 datagram 1| |||
| |||<-IPv4-in-IPv6 softwire
| |||
-----|-|||-------
/ | ||| \
| ISP core network |
\ | ||| /
-----|-|||-------
| |||
| |||2001:0:0:2::1
+------|-|||--------+
| | AFTR |
| v ||| |
|+--------+--------+|
|| Concentrator ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
| |129.0.0.1
IPv4 datagram 2 | |
-----|--|--------
/ | | \
| Internet |
\ | | /
-----|--|--------
| |
v |128.0.0.1
+-----+-----+
| IPv4 Host |
+-----------+
Figure 5: Outbound Datagram
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+-----------------+--------------+---------------+
| Datagram | Header field | Contents |
+-----------------+--------------+---------------+
| IPv6 Datagram 1 | IPv6 Dst | 2001:0:0:2::1 |
| | IPv6 Src | 2001:0:0:1::1 |
| | IPv4 Dst | 128.0.0.1 |
| | IPv4 Src | a.b.c.d |
| | TCP Dst | 80 |
| | TCP Src | 10000 |
| --------------- | ------------ | ------------- |
| IPv4 datagram 2 | IPv4 Dst | 128.0.0.1 |
| | IPv4 Src | 129.0.0.1 |
| | TCP Dst | 80 |
| | TCP Src | 5000 |
+-----------------+--------------+---------------+
Datagram header contents
When sending an IPv4 packet, the dual-stack lite host encapsulates it
in datagram 1 and forwards it to the AFTR over the softwire.
When it receives datagram 1, the concentrator in the AFTR hands the
IPv4 datagram to the NAT, which determines from its translation table
that the datagram received on Softwire_1 with TCP SRC port 10000
should be translated to datagram 3 with IP SRC address 129.0.0.1 and
TCP SRC port 5000.
Figure 6 shows an inbound message received at the AFTR. When the NAT
function in the AFTR receives datagram 1, it looks up the IP/TCP DST
in its translation table. In the example in Figure 3, the NAT
translates the TCP DST port to 10000, sets the IP DST address to
a.b.c.d and hands the datagram to the concentrator for transmission
over Softwire_1. The B4 in the dual-stack lite hosts decapsulates
IPv4 datagram from the inbound softwire datagram, and forwards it to
the host.
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+-------------------+
| |
|Host 192.0.0.2 |
|+--------+--------+|
|| B4 ||
|+--------+--------+|
+--------|||--------+
^ |||2001:0:0:1::1
IPv6 datagram 2 | |||
| |||<-IPv4-in-IPv6 softwire
| |||
-----|-|||-------
/ | ||| \
| ISP core network |
\ | ||| /
-----|-|||-------
| |||
| |||2001:0:0:2::1
+------|-|||--------+
| AFTR |
| | ||| |
|+--------+--------+|
|| Concentrator ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
^ |129.0.0.1
IPv4 datagram 1 | |
-----|--|--------
/ | | \
| Internet |
\ | | /
-----|--|--------
| |
| |128.0.0.1
+-----+-----+
| IPv4 Host |
+-----------+
Figure 6: Inbound Datagram
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+-----------------+--------------+---------------+
| Datagram | Header field | Contents |
+-----------------+--------------+---------------+
| IPv4 datagram 1 | IPv4 Dst | 129.0.0.1 |
| | IPv4 Src | 128.0.0.1 |
| | TCP Dst | 5000 |
| | TCP Src | 80 |
| --------------- | ------------ | ------------- |
| IPv6 Datagram 2 | IPv6 Dst | 2001:0:0:1::1 |
| | IPv6 Src | 2001:0:0:2::1 |
| | IPv4 Dst | a.b.c.d |
| | IP Src | 128.0.0.1 |
| | TCP Dst | 10000 |
| | TCP Src | 80 |
+-----------------+--------------+---------------+
Datagram header contents
14.2.2. Translation details
The translations happening in the AFTR are the same as in the
previous examples. The well known IPv4 address 192.0.0.2 out of the
192.0.0.0/29 (defined by IANA) range used by all the hosts are
disambiguated by the IPv6 source address of the softwire.
+---------------------------------+--------------------+
| Softwire-Id/IPv4/Prot/Port | IPv4/Prot/Port |
+---------------------------------+--------------------+
| 2001:0:0:1::1/a.b.c.d/TCP/10000 | 129.0.0.1/TCP/5000 |
+---------------------------------+--------------------+
Dual-Stack lite carrier-grade NAT translation table
The Softwire-Id is the IPv6 address assigned to the Dual-Stack host.
Each host has an unique Softwire-Id. The source IPv4 address is one
of the well-known IPv4 address. The AFTR could receive packets from
different hosts sourced from the same IPv4 well-known address from
different softwire tunnels. Similar to the gateway architecture, the
AFTR combines the Softwire-Id and IPv4 address/Port [Softwire-Id,
IPv4+Port] to uniquely identify the individual host.
15. Appendix C: Deployment considerations
15.1. AFTR service distribution and horizontal scaling
One of the key benefits of the dual-stack lite technology lies in the
fact it is tunnel based. That is, tunnel end-points may be anywhere
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in the service provider network.
Using the DHCPv6 tunnel end-point option, service providers can
create groups of users sharing the same AFTR. Those groups can be
merged or divided at will. This leads to an horizontally scaled
solution, where more capacity is added simply by adding more boxes.
As those groups of users can evolve over time, it is best to make
sure that AFTRs do not require per-user configuration in order to
provide service.
15.2. Horizontal scaling
A service provider can start using just a few AFTR centrally located.
Later, when more capacity is needed, more boxes can be added and
pushed to the edges of the access network. In case of a spike of
traffic, for example during the Olympic games or an important
political event, capacity can be quickly added in any location of the
network (tunnels can terminate anywhere) simply by splitting user
groups. Extra capacity can be later removed when the traffic returns
to normal by resetting the DHCPv6 tunnel end-point settings.
15.3. High availability
An important element in the design of the dual-stack lite technology
is the simplicity of implementation on the customer side. A simple
IP4-in-IPv6 tunnel and a default route over it is all is needed to
get IPv4 connectivity. Dealing with high availability is the
responsibility of the service provider, not the customer devices
implementing dual-stack lite. As such, a single IPv6 address of the
tunnel end-point is provided in the DHCPv6 option defined in
[I-D.ietf-softwire-ds-lite-tunnel-option]. The service provider can
use techniques such as anycast or various types of clusters to ensure
availability of the IPv4 service. The exact synchronization (or lack
thereof) between redundant AFTRs is out of scope for this document.
16. References
16.1. Normative references
[I-D.ietf-softwire-ds-lite-tunnel-option]
Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
Protocol for IPv6 (DHCPv6) Options for Dual- Stack Lite",
draft-ietf-softwire-ds-lite-tunnel-option-01 (work in
progress), January 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
December 1998.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines",
BCP 152, RFC 5625, August 2009.
16.2. Informative references
[I-D.bajko-v6ops-port-restricted-ipaddr-assign]
Bajko, G. and T. Savolainen, "Port Restricted IP Address
Assignment",
draft-bajko-v6ops-port-restricted-ipaddr-assign-02 (work
in progress), November 2008.
[I-D.cheshire-nat-pmp]
Cheshire, S., "NAT Port Mapping Protocol (NAT-PMP)",
draft-cheshire-nat-pmp-03 (work in progress), April 2008.
[I-D.droms-softwires-snat]
Droms, R. and B. Haberman, "Softwires Network Address
Translation (SNAT)", draft-droms-softwires-snat-01 (work
in progress), July 2008.
[I-D.durand-dual-stack-lite]
Durand, A., "Dual-stack lite broadband deployments post
IPv4 exhaustion", draft-durand-dual-stack-lite-00 (work in
progress), July 2008.
[I-D.ford-shared-addressing-issues]
Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing",
draft-ford-shared-addressing-issues-01 (work in progress),
October 2009.
[I-D.nishitani-cgn]
Nishitani, T., Yamagata, I., Miyakawa, S., Nakagawa, A.,
and H. Ashida, "Common Functions of Large Scale NAT
(LSN)", draft-nishitani-cgn-03 (work in progress),
November 2009.
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[I-D.templin-seal]
Templin, F., "The Subnetwork Encapsulation and Adaptation
Layer (SEAL)", draft-templin-seal-23 (work in progress),
August 2008.
[I-D.ymbk-aplusp]
Bush, R., "The A+P Approach to the IPv4 Address Shortage",
draft-ymbk-aplusp-05 (work in progress), October 2009.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations",
RFC 2663, August 1999.
[RFC2993] Hain, T., "Architectural Implications of NAT", RFC 2993,
November 2000.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, October 2008.
[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP", BCP 148, RFC 5508,
April 2009.
[RFC5571] Storer, B., Pignataro, C., Dos Santos, M., Stevant, B.,
Toutain, L., and J. Tremblay, "Softwire Hub and Spoke
Deployment Framework with Layer Two Tunneling Protocol
Version 2 (L2TPv2)", RFC 5571, June 2009.
[UPnP-IGD]
UPnP Forum, "Universal Plug and Play Internet Gateway
Device Standardized Gateway Device Protocol",
September 2006,
<http://www.upnp.org/standardizeddcps/igd.asp>.
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Author's Address
Alain Durand (editor)
Comcast
1, Comcast center
Philadelphia, PA 19103
USA
Email: alain_durand@cable.comcast.com
Durand Expires August 7, 2010 [Page 36]
