Softwires C. Zhou
Internet-Draft T. Tsou
Intended status: Standards Track Huawei Technologies
Expires: January 12, 2011 Y. Lee, Ed.
Comcast
G. Yang
China Telecom
July 11, 2010
Deployment DS-lite in Point-to-Point Access Network
draft-zhou-softwire-ds-lite-p2p-02
Abstract
Gateway-Initiated Dual-Stack lite (GI-DS-lite) is a proposal to
logically extend existing access tunnels beyond the access gateway to
DS-Lite Address Family Transition Router element (AFTR) using
softwires with an embedded context identifier. This memo describes a
deployment model using GI-DS-lite in Point-to-Point access network.
Status of this Memo
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This Internet-Draft will expire on January 12, 2011.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Scope and Requirements . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Current Deployment . . . . . . . . . . . . . . . . . . . . 4
3.2. DS-lite in Point-to-Point Access Network . . . . . . . . . 5
4. Requirements Language . . . . . . . . . . . . . . . . . . . . . 6
5. Proposed Alternative Context Identifier . . . . . . . . . . . . 6
6. Management of Devices behind CPE . . . . . . . . . . . . . . . 7
7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
10. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . . 8
11.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
GI-DS-lite [I-D.ietf-softwire-gateway-init-ds-lite] describes the use
of Gateway-Initiated softwire tunnels operating between the Gateway
and the Address Family Transition Router (AFTR) to conserve IPv4
addresses. Flows from multiple access devices (CPEs) can be
distinguished through use of Context Identifiers (CID). GI-DS-lite
describes an architecture where each CPE is a single device. It does
not cover the case where each CPE manages multiple hosts. This is
common in fixed network deployment and home network deployment over
air.
GI-DS-lite proposes few tunnel modes used for CID. One option is to
use Plain IP-in-IP. In this mode, a unique IPv4 address must be
assigned for each CPE from the gateway. As such, it does not support
CPEs using overlapped address. To support overlapped address space,
stateful tunnel (eg. GRE) is required between gateway and AFTR. It
is expensive to create one stateful tunnel per CPE especially in
fixed network non-mobility deployment.
DS-Extra-lite [I-D.arkko-dual-stack-extra-lite] describes that when
the CPE is connected to the gateway by point-to-point link rather
than shared media connection, it is unnecessary for the CID to be an
IP address. If another identifier with the required uniqueness
properties can be found (eg. VLAN and ATM PVC), the gateway can use
the per-interface identity to uniquely identify the CPE. This
relaxes the contraint of using CPE's IPv4 address for uniqueness.
This memo describes a framework to use the point-to-point identifier
and the IPv6 Flow Label [RFC3697] to create a unique binding in the
AFTR for CPEs using overlapped address space in the point-to-point
access network.
2. Scope and Requirements
This specification focuses on the point-to-point access network
deployment using GI-DS-lite. Other deployment scenarios are out of
scope. These are the assumptions of the network:
1. The access network is point-to-point.
2. The access network is not yet IPv6 enabled.
3. Avoid double-NAT.
4. Edge router does not perform NAT.
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5. Edge router uses plain IP-in-IPv6 to connect to AFTR.
6. Extend the point-to-point mapping to AFTR.
3. Overview
3.1. Current Deployment
Many operators use point-to-point (eg. PPP) to connect to their
customers. The operators give each customer a public IPv4 address.
Many customers also have a gateway (managed or unmanaged) which is a
NAT device managing the customer's internal network. Figure 1 shows
a common deployment architecture.
|
| IPv4 Internet
|
+------+------+
| Gateway |
+-------------+
/ \
Layer-3 / \ Layer-3
+----+ +----+
| ER | | ER |
+----+ +----+
/\ /\
/ \ / \ Pt-to-Pt
NAT/ \NAT NAT/ \NAT
+===+ +===+ +===+ +===+
| A | | B | | C | | D |
+===+ +===+ +===+ +===+
| | | |
--+-- --+-- --+-- --+--
| | | | | | | |
H1 H2 H3 H4 H5 H6 H7 H8
Access CPEs A,B,C,D all use 192.168.1.0/24
for their internal network.
Figure 1
Each CPE has been assigned a unique global IPv4 address and performs
NAT for the hosts, so Edge Router (ER) can uniquely identify the CPEs
by their IP addresses.
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3.2. DS-lite in Point-to-Point Access Network
When IPv4 addresses are scarce, operators may want to increase the
IPv4 address utilization by sharing a single IPv4 address to multiple
users. DS-Lite [I-D.ietf-softwire-dual-stack-lite] describes a
framework to implement B4 element in the CPE and encapsulate the IPv4
datagram inside an IPv6 datagram (IP-in-IPv6) to AFTR in the operator
network for NAT-ing. The AFTR uses the unique IPv6 address of the B4
to identify the CPE. This framework works well for both shared media
network and point-to-point access network, but it requires the
operator to upgrade the access network to IPv6.
In point-to-point access network, each CPE has a unique point-to-
point link. The operator can use the link information to identify
the CPE. In this specification, the operator does not give any IPv4
or IPv6 address to the CPE. Instead, each point-to-point interface
is an unnumbered interface. The CPE is still an IPv4 DHCP server for
its internal network, it continues to offer [RFC1918] addresses to
its managed hosts. In this memo, the CPE does not NAT the packets
coming from its hosts. Instead, the CPE simply puts the packets to
the point-to-point link and forward to the ER. When ER receives the
packet, it maps the point-to-point identifier to the IPv6 Flow Label
[RFC3697] and send to the AFTR for NAT. Figure 2 shows the
architecture.
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|
| IPv4 Internet
+--------+
| DS-lite| NAT Mappings:
| AFTR | (Flow Label, TCP port1 <->
+---++---+ a.b.c.d, TCP port2)
||
IPv6 || Softwire Tunnel (IP-in-IPv6)
|| (CID is the Flow Label)
||
+-----++------+
| Edge Router | Map IPv6 Flow Label to CID
+-------------+
/ \ Pt-to-Pt
/ \ unnumbered I/F
+===+ +===+
| A | | B | Access CPE A and B
+===+ +===+ use 192.168.1.0/24
| |
--+-- --+--
| | | |
H1 H2 H3 H4
.5 .6 .5 .6
Figure 2
In Figure 2, H1 and H3, and H2 and H4 use duplicate IP addresses.
Since CPE A and B do not have IP address, the ER cannot use the IP
address to returned packets to the hosts behind CPE A and B. Instead,
ER creates a binding table to map the point-to-point identifier to
the CPEs. Then, ER uses the IPv6 Flow Label [RFC3697] as the Context
Identifier for the GI-DS-lite tunnel. No stateful tunnel is required
between AFTR and ER.
4. 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].
5. Proposed Alternative Context Identifier
This memo proposes that an additional type of context identifier be
added to the set identified in GI-DS-lite. Where the tunnel between
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the Gateway and the AFTR is IP-in-IPv6, it is proposed to use the
IPv6 Flow Label as the context identifier.
The Flow Label is 20 bits, where the Context ID in GI-DS-lite is 32
bits. So, each softwire can support up to 2^20 or 1,048,576 CPEs.
To support more CPEs in a single ER, multiple softwires can be
provisioned between the ER and the AFTR.
6. Management of Devices behind CPE
Some operators manage the home devices (eg. IP STB and VoIP adaptor)
behind the CPE. This is done by port-forwarding the pre-configured
ports in the CPE. If the CPE implemented this specification, the
home device management traffic would be tunneled to the AFTR. The
AFTR would also need to support special port-forwarding rules to
allow in-bound connections to the home devices. This adds extra
complexity to the AFTR and consumes many ports in the AFTR for port-
forwarding.
Since this management traffic is internally used by the operator
only, the operator could address the CPE with [RFC1918]. This
address space is managed by the operator and each CPE is assigned a
unique RFC1918 address. The CPE contains the same port-forwarding
rules for the managed home devices. When the CPE receives packets
from the home devices, it will NAT the packet to the address assigned
to the point-to-point link and forward to the ER. For the packets
generated by the hosts, the CPE will use the specification to send
the traffic unmodified to the ER.
When the ER receives packets sourced from this [RFC1918] address
space, it should not forward these packets to the AFTR via the
softwire. Instead, the ER should forward the packets to the internal
management network. To make the ER forwarding rule simple, the CPE
management address space must not overlap with the address space used
by the CPE for its internal hosts.
7. Conclusion
We present a framework to deploy GI-DS-lite in point-to-point access
network. This framework promotes IPv6 deployment from the core to
the edge. When IPv6 is ready in the access network, the operators
can either upgrade the CPE to B4 element and migrate to classic DS-
lite deployment or provision dual-stack to the CPE and continue to
use GI-DS-lite.
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8. Acknowledgements
TBD
9. IANA Considerations
This memo includes no request to IANA.
10. Security Considerations
See the security considerations for [RFC3697] and
[I-D.ietf-softwire-dual-stack-lite]. This proposal adds no further
security considerations.
11. References
11.1. Normative References
[I-D.ietf-softwire-dual-stack-lite]
Durand, A., Droms, R., Haberman, B., Woodyatt, J., Lee,
Y., and R. Bush, "Dual-Stack Lite Broadband Deployments
Following IPv4 Exhaustion",
draft-ietf-softwire-dual-stack-lite-05 (work in progress),
July 2010.
[I-D.ietf-softwire-gateway-init-ds-lite]
Brockners, F., Gundavelli, S., Speicher, S., and D. Ward,
"Gateway Initiated Dual-Stack Lite Deployment",
draft-ietf-softwire-gateway-init-ds-lite-00 (work in
progress), May 2010.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3697] Rajahalme, J., Conta, A., Carpenter, B., and S. Deering,
"IPv6 Flow Label Specification", RFC 3697, March 2004.
11.2. Informative References
[]
Arkko, J. and L. Eggert, "Scalable Operation of Address
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Translators with Per-Interface Bindings",
draft-arkko-dual-stack-extra-lite-00 (work in progress),
February 2010.
Authors' Addresses
Cathy Zhou
Huawei Technologies
Section B, Huawei Industrial Base
Bantian Longgang
Shenzhen 518129
P.R. China
Email: cathyzhou@huawei.com
URI: http://www.huawei.com
Tina Tsou
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
P.R. China
Email: tena@huawei.com
URI: http://www.huawei.com
Yiu L. Lee (editor)
Comcast
One Comcast Center
Philadelphia 19103
U.S.A.
Email: yiu_lee@cable.comcast.com
URI: http://www.comcast.com
GL Yang
China Telecom
109 East Zhongshan Road, Tiahne District
Guangzhou
P.R. China
Email: yanggl@gsta.com
URI: http://www.chinatelecom.com.cn
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