Internet Engineering Task Force A. Durand
Internet-Draft Juniper Networks
Intended status: Standards Track R. Droms
Expires: September 4, 2011 Cisco
J. Woodyatt
Apple
Y. Lee
Comcast
March 3, 2011
Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion
draft-ietf-softwire-dual-stack-lite-07
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 in service provider networks. 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 Network Address Translation (NAT).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 4, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements language . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Deployment scenarios . . . . . . . . . . . . . . . . . . . . . 5
4.1. Access model . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. CPE . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.3. Directly connected device . . . . . . . . . . . . . . . . 7
5. B4 element . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 7
5.3. Fragmentation and Reassembly . . . . . . . . . . . . . . . 7
5.4. AFTR discovery . . . . . . . . . . . . . . . . . . . . . . 8
5.5. DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.6. Interface initialization . . . . . . . . . . . . . . . . . 8
5.7. Well-known IPv4 address . . . . . . . . . . . . . . . . . 9
6. AFTR element . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 9
6.2. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 9
6.3. Fragmentation and Reassembly . . . . . . . . . . . . . . . 9
6.4. DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.5. Well-known IPv4 address . . . . . . . . . . . . . . . . . 10
6.6. Extended binding table . . . . . . . . . . . . . . . . . . 10
7. Network Considerations . . . . . . . . . . . . . . . . . . . . 10
7.1. Tunneling . . . . . . . . . . . . . . . . . . . . . . . . 10
7.2. VPN . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.3. Multicast considerations . . . . . . . . . . . . . . . . . 11
8. NAT considerations . . . . . . . . . . . . . . . . . . . . . . 11
8.1. NAT pool . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.2. NAT conformance . . . . . . . . . . . . . . . . . . . . . 11
8.3. Application Level Gateways (ALG) . . . . . . . . . . . . . 11
8.4. Sharing global IPv4 addresses . . . . . . . . . . . . . . 11
8.5. Port forwarding / keep alive . . . . . . . . . . . . . . . 12
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
11. Security Considerations . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative references . . . . . . . . . . . . . . . . . . . 14
12.2. Informative references . . . . . . . . . . . . . . . . . . 14
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Appendix A. Deployment considerations . . . . . . . . . . . . . . 16
A.1. AFTR service distribution and horizontal scaling . . . . . 16
A.2. Horizontal scaling . . . . . . . . . . . . . . . . . . . . 16
A.3. High availability . . . . . . . . . . . . . . . . . . . . 16
A.4. Logging . . . . . . . . . . . . . . . . . . . . . . . . . 16
Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 17
B.1. Gateway based architecture . . . . . . . . . . . . . . . . 17
B.1.1. Example message flow . . . . . . . . . . . . . . . . . 19
B.1.2. Translation details . . . . . . . . . . . . . . . . . 23
B.2. Host based architecture . . . . . . . . . . . . . . . . . 24
B.2.1. Example message flow . . . . . . . . . . . . . . . . . 27
B.2.2. Translation details . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
The common thinking for more than 10 years has been that the
transition to IPv6 will be based solely on the dual stack model and
that most things would be converted this way before we ran out of
IPv4. However, this has not happened. The IANA free pool of IPv4
addresses has now depleted, well before sufficient IPv6 deployment
had taken place. As a result, many IPv4 services have to continue to
be provided even under severely limited address space.
This document specifies the dual-stack lite technology which is aimed
at better aligning the costs and benefits in service provider
networks. Dual-stack lite will enable both continued support for
IPv4 services and incentives for the deployment of IPv6. It also de-
couples IPv6 deployment in the service provider network from the rest
of the Internet, making incremental deployment easier.
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 latter 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.
This document will first present some deployment scenario and then
define the behavior of the two elements of the dual-stack lite
technology: the B4 and the AFTR. It will then go into networking and
NAT-ing considerations.
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].
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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).
Dual-stack is defined in [RFC4213].
NAT related terminology is defined in [RFC4787].
CPE stands for Customer Premise Equipment. This is the layer 3
device in the customer premise that is connected to the service
provider network. That device is often a home gateway. However,
sometimes computers are directly attached to the service provider
network. In such cases, such computers can be viewed as CPEs as
well.
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 leveraged to enable customers and their applications to
control how the NAT function of the AFTR is performed.
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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.
4.2. CPE
This section describes home Local Area networks characterized by the
presence of a home gateway, or CPE, provisioned only with IPv6 by the
service provider.
A DS-Lite CPE is an IPv6 aware CPE with a B4 Interface implemented in
the WAN interface.
A DS-Lite CPE SHOULD NOT operate a NAT function between an internal
interface and a B4 interface, as the NAT function will be performed
by the AFTR in the 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 host decides to use another IPv4 DNS server,
the DS-Lite CPE will forward those DNS requests via the B4 interface,
the same way it forwards any regular IPv4 packets. However, each DNS
request will create a binding in the AFTR. A large number of DNS
requests may have direct impact to the AFTR's NAT table utilization.
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.
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4.3. Directly connected device
In broadband home networks, some devices are directly connected to
the broadband service provider. They are connected straight to a
modem, without a home gateway. Those devices are, in fact, acting as
CPEs.
Under this scenario, the customer device is a dual-stack capable host
that is only provisioned by the service provider with IPv6 only. 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/CPE 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.
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 CPE, 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
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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 providers 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].
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 SHOULD
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.
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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 MAY use any other addresses within
the 192.0.0.0/29 range.
Note: a range of addresses has been reserved for this purpose. The
intent is to accommodate nodes implementing multiple B4 elements.
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.
6.2. Encapsulation
The tunnel is a point-to-multipoint IPv4-in-IPv6 tunnel ending at the
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 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-weight 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
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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 require 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.
Methods to avoid fragmentation, such as rewriting the TCP MSS option
or using technologies such as Subnetwork Encapsulation and Adaptation
Layer defined in [RFC5320] 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
packets will flow through the AFTR element.
6.5. Well-known IPv4 address
The AFTR MAY use the well-known 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 is
used to 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
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over to the IPv6 headers and vice versa.
7.2. VPN
Dual-stack lite implementations SHOULD NOT interfere with the
functioning of IPv4 or IPv6 VPNs.
7.3. Multicast considerations
Multicast is out-of-scope in this document.
8. NAT considerations
8.1. NAT pool
The AFTR MAY be provisioned with different NAT pools. The address
range in the pools may be disjoint but must not be overlapped.
Operators may implement policies in the AFTR to assign clients in
different pools. For example, a AFTR can have two interfaces. Each
interface will have a disjoint pool NAT assigned to it. In another
case, a policy can apply to the AFTR that a set of B4s will use NAT
pool 1 and a different set of B4s will use NAT pool 2.
8.2. NAT conformance
A dual-stack lite AFTR SHOULD implement behavior conforming to the
best current practice, currently documented in [RFC4787] and
[RFC5382]. Other discusions about carrier-grade NATs can be found in
[I-D.nishitani-cgn].
8.3. Application Level Gateways (ALG)
AFTR performs NAT-44 and inherits the limitations of NAT. Some
protocols required ALGs in the NAT device to traverse through the
NAT. For example: SIP and ICMP require ALG to work properly. ALGs
consume resources and there are many different types of ALGs. The
AFTR is a shared network device that supports a large number of B4
elements. It is impossible for the AFTR to implement every current
and future ALGs. This specification only requires that the AFTR MUST
support [RFC5508]. Implementers can decide to implement other ALGs
in their implementations.
8.4. Sharing global IPv4 addresses
AFTR shares a single IP to multiple users. This helps to increase
the IPv4 address utilization. However, it also brings some issues
such as logging and lawful intercept. More considerations on sharing
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the port space of IPv4 addresses can be found in
[I-D.ietf-intarea-shared-addressing-issues].
8.5. Port forwarding / keep alive
Work on a control plane to the carrier-grade NAT is done in the PCP
working group at IETF. The PCP protocol enables applications to
directly negotiate with the NAT to open ports and negotiate liefetime
values to avoid keep-alive traffic. More on PCP can be found in
[I-D.ietf-pcp-base].
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 feedback. 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
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 CPE 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. The AFTR
should have the capability to log the tunnel-id, protocol, ports/IP
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addresses, and the creation time of the NAT binding to uniquely
identify the user sessions. Exact details of what is logged are
implementation specific and out of scope for this document.
The AFTR performs translation functions for interior IPv4 hosts using
RFC 1918 addresses or the IANA reserved address range (TBA by IANA).
In some circumstances, ISP may provision policies in the AFTR and
instructs the AFTR to bypass translation functions based on <IPv4
Address, port number, protocol>. When the AFTR receives a packet
with matching information of the policy from the interior host, the
AFTR can simply forward without translation. The addresses, ports
and protocols information must be provisioned on the AFTR before
receiving the packet. The provisioning mechanism is out-of-scope of
this specification.
When decapsulating packets, the AFTR MUST only forward packets
sourced by RFC 1918 addresses, IANA reserved address range, or any
other out-of-band pre-authorized addresses. The AFTR MUST drop all
others packets. 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 a TCP SYN ACK attack [RFC4987]. 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 a 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 sharing IPv4 addresses can be found in
[I-D.ietf-intarea-shared-addressing-issues]. Other considerations
and recommendations on logging can be found in
[I-D.ietf-intarea-server-logging-recommendations].
AFTRs should support ways to limit service only to registered
customers. One simple option is to implement IPv6 ingress filter on
the AFTR's tunnel interface to accept only the IPv6 address range
defined in the filter.
12. References
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12.1. Normative references
[I-D.ietf-softwire-ds-lite-tunnel-option]
Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
Protocol for IPv6 (DHCPv6) Option for Dual- Stack Lite",
draft-ietf-softwire-ds-lite-tunnel-option-09 (work in
progress), March 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
12.2. Informative references
[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.ietf-intarea-server-logging-recommendations]
Durand, A., Gashinsky, I., Lee, D., and S. Sheppard,
"Logging recommendations for Internet facing servers",
draft-ietf-intarea-server-logging-recommendations-03 (work
in progress), February 2011.
[I-D.ietf-intarea-shared-addressing-issues]
Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing",
draft-ietf-intarea-shared-addressing-issues-04 (work in
progress), February 2011.
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[I-D.ietf-pcp-base]
Wing, D., Cheshire, S., Boucadair, M., Penno, R., and F.
Dupont, "Port Control Protocol (PCP)",
draft-ietf-pcp-base-06 (work in progress), February 2011.
[I-D.nishitani-cgn]
Yamagata, I., Miyakawa, S., Nakagawa, A., and H. Ashida,
"Common requirements for IP address sharing schemes",
draft-nishitani-cgn-05 (work in progress), July 2010.
[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.
[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common
Mitigations", RFC 4987, August 2007.
[RFC5320] Templin, F., "The Subnetwork Encapsulation and Adaptation
Layer (SEAL)", RFC 5320, February 2010.
[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.
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Appendix A. Deployment considerations
A.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
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.
A.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.
A.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.
A.4. Logging
DS-Lite AFTR implementation should offer the possibility to log NAT
binding creations or other ways to keep track of the ports/IP
addresses used by customers. This is both to support
troubleshooting, which is very important to service providers trying
to figure out why something may not be working, as well as to meet
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region-specific requirements for responding to legally-binding
requests for information from law enforcement authorities.
Appendix B. Examples
B.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 devices is important.
Consider a scenario where a Dual-Stack lite CPE is provisioned only
with IPv6 in the WAN port, no IPv4. The CPE acts as an IPv4 DCHP
server for the LAN network (wireline and wireless) handing out
RFC1918 addresses. In addition, the CPE may support IPv6 Auto-
Configuration and/or DHCPv6 server for the LAN network. When an
IPv4-only device connects to the CPE, that CPE will hand it out a
RFC1918 address. When a dual-stack capable device connects to the
CPE, that CPE will hand out a RFC1918 address and a global IPv6
address to the device. Besides, the CPE 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 CPE natively. The CPE will route the traffic upstream to the
default gateway.
When the device accesses IPv4 service, it will source the IPv4
datagram with the RFC1918 address and send the IPv4 datagram to the
CPE. The CPE will encapsulate the IPv4 datagram inside the IPv4-in-
IPv6 softwire tunnel and forward the IPv6 datagram to the AFTR. This
contrasts what the CPE normally does today, which is, 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:db8:0:1::1
|||
|||<-IPv4-in-IPv6 softwire
|||
-------|||-------
/ ||| \
| ISP core network |
\ ||| /
-------|||-------
|||
|||2001:db8:0:2::1
+--------|||--------+
| AFTR |
|+--------+--------+|
|| Concentrator ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
|192.0.2.1
|
--------|--------
/ | \
| Internet |
\ | /
--------|--------
|
|198.51.100.1
+-----+-----+
| 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.
B.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
(192.0.2.1/5000). 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
192.0.2.1 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:db8:0:1::1
IPv6 datagram 2| |||
| |||<-IPv4-in-IPv6 softwire
| |||
-----|-|||-------
/ | ||| \
| ISP core network |
\ | ||| /
-----|-|||-------
| |||
| |||2001:db8:0:2::1
+------|-|||--------+
| | AFTR |
| v ||| |
|+--------+--------+|
|| Concentrartor ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
| |192.0.2.1
IPv4 datagram 3 | |
| |
-----|--|--------
/ | | \
| Internet |
\ | | /
-----|--|--------
| |
v |198.51.100.1
+-----+-----+
| IPv4 Host |
+-----------+
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Figure 2: Outbound Datagram
+-----------------+--------------+-----------------+
| Datagram | Header field | Contents |
+-----------------+--------------+-----------------+
| IPv4 datagram 1 | IPv4 Dst | 198.51.100.1 |
| | IPv4 Src | 10.0.0.1 |
| | TCP Dst | 80 |
| | TCP Src | 10000 |
| --------------- | ------------ | ------------- |
| IPv6 Datagram 2 | IPv6 Dst | 2001:db8:0:2::1 |
| | IPv6 Src | 2001:db8:0:1::1 |
| | IPv4 Dst | 198.51.100.1 |
| | IPv4 Src | 10.0.0.1 |
| | TCP Dst | 80 |
| | TCP Src | 10000 |
| --------------- | ------------ | ------------- |
| IPv4 datagram 3 | IPv4 Dst | 198.51.100.1 |
| | IPv4 Src | 192.0.2.1 |
| | 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
192.0.2.1 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:db8:0:1::1
IPv6 datagram 2 | |||
| |||<-IPv4-in-IPv6 softwire
| |||
-----|-|||-------
/ | ||| \
| ISP core network |
\ | ||| /
-----|-|||-------
| |||
| |||2001:db8:0:2::1
+------|-|||--------+
| AFTR |
|+--------+--------+|
|| Concentrator ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
^ |192.0.2.1
IPv4 datagram 1 | |
| |
-----|--|--------
/ | | \
| Internet |
\ | | /
-----|--|--------
| |
| |198.51.100.1
+-----+-----+
| IPv4 Host |
+-----------+
Figure 3: Inbound Datagram
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+-----------------+--------------+-----------------+
| Datagram | Header field | Contents |
+-----------------+--------------+-----------------+
| IPv4 datagram 1 | IPv4 Dst | 192.0.2.1 |
| | IPv4 Src | 198.51.100.1 |
| | TCP Dst | 5000 |
| | TCP Src | 80 |
| --------------- | ------------ | ------------- |
| IPv6 Datagram 2 | IPv6 Dst | 2001:db8:0:1::1 |
| | IPv6 Src | 2001:db8:0:2::1 |
| | IPv4 Dst | 10.0.0.1 |
| | IP Src | 198.51.100.1 |
| | TCP Dst | 10000 |
| | TCP Src | 80 |
| --------------- | ------------ | ------------- |
| IPv4 datagram 3 | IPv4 Dst | 10.0.0.1 |
| | IPv4 Src | 198.51.100.1 |
| | TCP Dst | 10000 |
| | TCP Src | 80 |
+-----------------+--------------+-----------------+
Datagram header contents
B.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:db8:0:1::1/10.0.0.1/TCP/10000 | 192.0.2.1/TCP/5000 |
+------------------------------------+--------------------+
Dual-Stack lite carrier-grade NAT translation table
The Softwire-Id is the IPv6 address assigned to the Dual-Stack lite
CPE. 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
CPE. 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.
B.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 CPE 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:db8:0:1::1
|||
|||<-IPv4-in-IPv6 softwire
|||
-------|||-------
/ ||| \
| ISP core network |
\ ||| /
-------|||-------
|||
|||2001:db8:0:2::1
+--------|||--------+
| AFTR |
|+--------+--------+|
|| Concentrator ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
|192.0.2.1
|
--------|--------
/ | \
| Internet |
\ | /
--------|--------
|
|198.51.100.1
+-----+-----+
| 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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B.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
(192.0.2.1/5000). 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 192.0.2.1 and TCP SRC port 5000 in the
Internet.
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+-------------------+
| |
|Host 192.0.0.2 |
|+--------+--------+|
|| B4 ||
|+--------+--------+|
+--------|||--------+
| |||2001:db8:0:1::1
IPv6 datagram 1| |||
| |||<-IPv4-in-IPv6 softwire
| |||
-----|-|||-------
/ | ||| \
| ISP core network |
\ | ||| /
-----|-|||-------
| |||
| |||2001:db8:0:2::1
+------|-|||--------+
| | AFTR |
| v ||| |
|+--------+--------+|
|| Concentrator ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
| |192.0.2.1
IPv4 datagram 2 | |
-----|--|--------
/ | | \
| Internet |
\ | | /
-----|--|--------
| |
v |198.51.100.1
+-----+-----+
| IPv4 Host |
+-----------+
Figure 5: Outbound Datagram
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+-----------------+--------------+-----------------+
| Datagram | Header field | Contents |
+-----------------+--------------+-----------------+
| IPv6 Datagram 1 | IPv6 Dst | 2001:db8:0:2::1 |
| | IPv6 Src | 2001:db8:0:1::1 |
| | IPv4 Dst | 198.51.100.1 |
| | IPv4 Src | a.b.c.d |
| | TCP Dst | 80 |
| | TCP Src | 10000 |
| --------------- | ------------ | ------------- |
| IPv4 datagram 2 | IPv4 Dst | 198.51.100.1 |
| | IPv4 Src | 192.0.2.1 |
| | 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 192.0.2.1 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:db8:0:1::1
IPv6 datagram 2 | |||
| |||<-IPv4-in-IPv6 softwire
| |||
-----|-|||-------
/ | ||| \
| ISP core network |
\ | ||| /
-----|-|||-------
| |||
| |||2001:db8:0:2::1
+------|-|||--------+
| AFTR |
| | ||| |
|+--------+--------+|
|| Concentrator ||
|+--------+--------+|
| |NAT| |
| +-+-+ |
+---------|---------+
^ |192.0.2.1
IPv4 datagram 1 | |
-----|--|--------
/ | | \
| Internet |
\ | | /
-----|--|--------
| |
| |198.51.100.1
+-----+-----+
| IPv4 Host |
+-----------+
Figure 6: Inbound Datagram
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+-----------------+--------------+-----------------+
| Datagram | Header field | Contents |
+-----------------+--------------+-----------------+
| IPv4 datagram 1 | IPv4 Dst | 192.0.2.1 |
| | IPv4 Src | 198.51.100.1 |
| | TCP Dst | 5000 |
| | TCP Src | 80 |
| --------------- | ------------ | ------------- |
| IPv6 Datagram 2 | IPv6 Dst | 2001:db8:0:1::1 |
| | IPv6 Src | 2001:db8:0:2::1 |
| | IPv4 Dst | a.b.c.d |
| | IP Src | 198.51.100.1 |
| | TCP Dst | 10000 |
| | TCP Src | 80 |
+-----------------+--------------+-----------------+
Datagram header contents
B.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:db8:0:1::1/a.b.c.d/TCP/10000 | 192.0.2.1/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.
Durand, et al. Expires September 4, 2011 [Page 31]
Internet-Draft Dual-stack lite March 2011
Authors' Addresses
Alain Durand
Juniper Networks
1194 North Mathilda Avenue
Sunnyvale, CA 94089-1206
USA
Email: adurand@juniper.net
Ralph Droms
Cisco
1414 Massachusetts Avenue
Boxborough, MA 01714
USA
Email: rdroms@cisco.com
James Woodyatt
Apple
1 Infinite Loop
Cupertino, CA 95014
USA
Email: jhw@apple.com
Yiu L. Lee
Comcast
One Comcast Center
Philadelphia, PA 19103
USA
Email: yiu_lee@cable.comcast.com
Durand, et al. Expires September 4, 2011 [Page 32]
