One document matched: draft-cui-softwire-b4-translated-ds-lite-02.txt
Differences from draft-cui-softwire-b4-translated-ds-lite-01.txt
Network Working Group Y. Cui
Internet-Draft J. Wu
Intended status: Standards Track P. Wu
Expires: April 2, 2012 Tsinghua University
Q. Sun
C. Xie
China Telecom
C. Zhou
Huawei Technologies
Y. Lee
Comcast
September 30, 2011
Lightweight 4over6 in access network
draft-cui-softwire-b4-translated-ds-lite-02
Abstract
The dual-stack lite mechanism provide an IPv4 access method over IPv6
ISP network for end users. Dual-Stack Lite enables an IPv6 provider
to share IPv4 addresses among customers by combining IPv4-in-IPv6
tunnel and Carrier Grade NAT. However, in dual-stack lite, CGN has
to maintain active NAT sessions, which could become the performance
bottom-neck due to high dynamic s of NAT entries, memory cost and log
issue. This document propose the lightweight 4over6 mechanism which
moves the translation function from tunnel concentrator (AFTR) to
initiators (B4s), and hence reduce the mapping scale on the
concentrator to per-customer level. For NAT44 translation usage, the
mechanism will allocate port restricted IPv4 addresses to initiators
in a flexible way independent of IPv6 network in the middle.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 2, 2012.
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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
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Lightweight 4over6 Overview . . . . . . . . . . . . . . . . . 7
5. Port Restricted IPv4 Address Allocation . . . . . . . . . . . 8
6. Lightweight 4over6 Initiator Behavior . . . . . . . . . . . . 9
7. Lightweight 4over6 Concentrator Behavior . . . . . . . . . . . 10
8. ICMP processing . . . . . . . . . . . . . . . . . . . . . . . 11
9. Mechanism Analysis . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
Dual-stack lite technology[RFC6333] provides IPv4 access over IPv6
access network. Dual-Stack lite (DS-lite) also mitigates IPv4
address exhaustion by sharing public IPv4 addresses amongst users.
The B4 element establishes an IPv4-in-IPv6 softwire to the AFTR and
encapsulates the IPv4 packets into the softwire. When AFTR receives
the IPv6 packets, it will decapsulate them and perform NAT-44 on the
packets. This procedure allows AFTR to dynamically assign sessions
to users when needed; hence, increases port-sharing radio and
utilization. There is a trade-off, though. The AFTR is required to
maintain active NAT sessions. In a centralized deployment models
where one AFTR serves thousands of users, the large numbers of NAT
sessions may become performance bottom-neck. First, maintaining
active NAT sessions requires AFTR constantly creating and purging NAT
sessions. Second, a large NAT table demands more processing power
for searching and more memory space. In addition, dynamic session-
based NAT will create large number of log entries, which will also be
a challenging problem.
To address these issues, we propose an extension to DS-lite. We
propose to create rule mapping in the AFTR and distributes the
dynamic NAT table into B4 elements. The B4 element will be
provisioned with an IPv6 address, an IPv4 address and a port-range.
The IPv6 address will be used to create the Softwire. The IPv4
address and port-range will be used for NAT-44 in the home
gateway(CPE). Most CPE have been performing NAT-44 today. The CPE
will perform PAT on user's packets with the IPv4 address and port-
range provisioned by the ISP. The packets are forwarded between the
CPE and the AFTR by IPv6 encapsulation over the tunnel. The AFTR
will maintain a static mapping entry with the IPv6 address, IPv4
address and port-range per user. For inbound IPv4 packet on AFTR, it
would use the IPv4 destination address and port as the index and use
the forwarding rule in the static mapping table to encapsulate the
packets to the destination CPE. The AFTR would not create NAT entry
per sessions. This will significantly reduce the AFTR's NAT table
size.
Compared to DS-lite, this extension reduces the AFTR NAT table size.
Each entry represents a B4 element. This also relaxes the
requirement to create a log entry per dynamic session. AFTR only
needs to keep a log entry per B4 element. This is also an extended
case which covers addressing sharing for
[I-D.cui-softwire-host-4over6]. However, the extension will decrease
IPv4 address utilization. Moreover, since port randomization
algorithm must use ports within this port-range, it may cause the
port randomization algorithm more predictable.
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Compared to stateless solutions with port range/set allocation such
as 4rd, this mechanism is suitable for operators who prefers to keep
IPv6 and IPv4 addressing separated. For example, an operator may
want to provide IPv4 with an on-demand way in its IPv6 network, the
dynamic allocation of IPv4 address and port makes more efficient
usage of IPv4 resource. Another example is that an operator may only
have many small and discontinuous IPv4 blocks available to provide
IPv4 over IPv6, rather than a few big IPv4 blocks. This mechanism
keeps dynamic feature of IPv4-IPv6 address binding as in DS-Lite, so
it won't require to administrate and manage many 4rd domains in the
network and mapping rules in the CPEs.
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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 [RFC2119].
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3. Terminology
Starting from here, the document will use the terminologies of
lightweight 4over6 instead of DS-lite for distinction.
Lightweight 4over6: lightweight 4over6 is an IPv4-over-IPv6 hub and
spoke mechanism proposed in this document, which supports address
sharing to deal with IPv4 address exhaustion, and places the IPv4
translation on the initiator side.
Lightweight 4over6 initiator (or "initiator" for short): the tunnel
initiator in lightweight 4over6 mechanism. The lightweight 4over6
initiator could be a host directly connected to IPv6, or an dual-
stack CPE in front of an IPv4 local network. It is responsible for
IPv4 public-private translation besides tunnel encapsulation and
decapsulation.
Lightweight 4over6 concentrator (or "concentrator" for short): the
tunnel concentrator in lightweight 4over6 mechanism. The lightweight
4over6 concentrator connects the ISP IPv6 network and IPv4 Internet.
It provides tunnel encapsulation and decapsulation but no IPv4
public-private translation.
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4. Lightweight 4over6 Overview
Figure 1 provides an overview of the lightweight 4over6 mechanism. A
lightweight 4over6 initiator which can be either an IPv6 hosts or
CPE, and the lightweight 4over6 concentrator are separated by the
IPv6 network in the middle, so they use IPv4-in-IPv6 tunnel to build
IPv4 connectivity. An initiator uses IPv4 address with restricted
port range for this IPv4 connectivity, which is acquired through
either DHCPv4 with the concentrator, or through PCP with the PCP
server. The concentrator keeps the mapping between initiator's IPv6
address and the allocated IPv4 address + port range.
+-------------------------+
| IPv6 ISP Network |
| |
+---------+ |
|LW 4over6|Host |
|Initiator|===============+---------+ +-----------+
+---------+ |LW 4over6| | IPv4 |
+--------+ | IPv4-in-IPv6 |Concen- |---| Internet |
| | +---------+ |trator | | |
|IPv4 LAN|--|LW 4over6|===============+---------+ +-----------+
| | |Initiator|CPE |DHCPv4
+--------+ +---------+ +----------+ |Server(Relay)
| |PCP Server| |
| +----------+ |
+-------------------------+
Figure 1 Lightweight 4over6 overview
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5. Port Restricted IPv4 Address Allocation
As is described above, a lightweight 4over6 initiator needs the
public address and port for stateful translation. It's obvious that
individual address + port allocation when required is not efficient
due to round-trip time delay and high signaling volume caused.
Besides, that way can't save the mapping amount at all. A practical
manner would be allocating a group of address + port at one time
beforehand, i.e., allocating IPv4 address with a port range, which is
known as "restricted address".
To our knowledge there're two methods which are probably suitable for
restricted address allocation from concentrator to initiator. One is
extending DHCP to support address allocation with port range
embedded. [I-D.bajko-pripaddrassign] discusses this DHCP usage. In
this special context, we need to build the DHCPv4 procedure over IPv6
[I-D.cui-softwire-dhcp-over-tunnel]. The other is extending PCP to
support port range control. See [I-D.tsou-pcp-natcoord] for details.
Adopting either method, An initiator can get port restricted IPv4
addresses allocated dynamically from the concentrator, i.e. the
dynamic mapping rule between IPv4 address, port range and IPv6
address can be passed down to the initiator in the initiation phase.
Unlike stateless 4over6 solutions such as
[I-D.murakami-softwire-4rd], the port restricted address allocation
in lightweight 4over6 has no requirement on careful planning of the
IPv6 domain range, IPv4/IPv6 mapping relationship, prefix length and
multiplex ratio, etc. It is quite flexible for ISPs to manage the
IPv6 access network and have no impact on IPv6 routing.
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6. Lightweight 4over6 Initiator Behavior
A lightweight 4over6 initiator should support either extended DHCP
client, or extended PCP client, as is described above. When
requiring IPv4 access, the initiator would run either client to get a
dynamic port restricted IPv4 address, and renew/extend it when the
lease/lifetime is about to expire.
The data plane functions of the initiator includes translation and
encapsulation/decapsulation. For CPE initiator case, the initiator
runs a standard local NAT44 with the address pool consist of the
allocated port restricted address. When sending out an IPv4 packet
with private source address, it performs NAT44 function and
translates the source address into public. Then it encapsulates the
packet with concentrator's IPv6 address as destination IPv6 address,
and forward it to the concentrator. When receiving an IPv4-in-IPv6
packet from the concentrator, the initiator decapsulates the IPv6
packet to get the IPv4 packet with public destination IPv4 address.
Then it performs NAT44 function and translates the destination
address into private.
For host initiator case, the host gets public address directly. It
is also suggested that the host run a local NAT to map randomly
generated ports into the restricted, valid port range. Private-
public address translation would not be needed in this NAT. Another
solution is to have the IP stack to only assign ports within the
restricted, valid range to applications. Either way the host
guarantees that every port number in the packets sent out by itself
falls into the allocated port range.
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7. Lightweight 4over6 Concentrator Behavior
The lightweight 4over6 concentrator should either allocate port
restricted addresses directly(perform an extended DHCPv4 server, or
an extended PCP server), or leave the allocation to dedicated DHCP/
PCP server(and perform a relay in DHCP case). When accomplishing one
such allocation, the concentrator simultaneously install a mapping
entry into the mapping table. This entry consists of the public IPv4
address, the port range and initiator's IPv6 address. Its lifetime
is set according to the allocation. It'll be used for encapsulation
of inbound packets. This mapping entry would be deleted when the
lifetime expires, and refresh its lifetime when the initiator renews/
extends the allocation.
The data plane functions of the concentrator is purely encapsulation
and decapsulation. When receiving an IPv4-in-IPv6 packet from an
initiator, the concentrator decapsulates it and forwards it to IPv4
Internet. When receiving an IPv4 packet from the Internet, it uses
the destination address and port from this packet to lookup the
destination initiator's IPv6 address in the mapping table. Then the
concentrator encapsulates this packet using the IPv6 address found in
the table as IPv6 destination address, and forwards it to the correct
initiator based on native IPv6 routing. Hence there is no port-range
routing in IPv6 network anymore.
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8. ICMP processing
ICMP availability would become a challenge in port restricted address
environment. To support ICMP "session" initiated from a lightweight
4over6 initiator, the mechanism divides ICMP id field in the same way
with dividing port space, i.e. each initiator will get the ICMP id
range which is identical to the allocated port range. An initiator
only uses the allocated address and restricted id range when send out
an ICMP request. Hence the concentrator can encapsulate the
corresponding ICMP reply correctly according to the ICMP id field.
The inbound ICMP request would be left unsupported on the
concentrator, which is the similar behavior of NAT/CGN. See details
about ICMP processing in section 4.2 of [I-D.sun-v6ops-laft6]
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9. Mechanism Analysis
Compared with original dual-stack lite, lightweight 4over6 removes
the translation burden from the concentrator and distribute the job
to initiators on user-side. Also it decreases the state scale on
concentrator from per-session level down to per-user level. This
would significantly reduce the hardware cost of the concentrator, and
relieve the situation that the concentrator becomes the performance
bottleneck. Leveraging lightweight 4over6, one concentrator can
serve a lot more customers.
Besides, since this mechanism reduces the number of simultaneous
address mappings of each customer on concentrator to one, it makes
concentrator logging much more feasible. Moreover, locating the
translation on user side eases the ALG and NAT referral problem since
it'll be no different from the situation of local NAT in today's IPv4
network. Solutions like uPnP already exist for quite a long time.
Most current CPEs have already implemented NAT44 functionalities,
lightweight 4over6 would not bring a lot more complexity to existing
CPEs.
Lightweight 4over6 allocates port restricted address independent of
the IPv6 network in the middle. No specific IPv6 address format is
required. IPv4 and IPv6 addressing and routing remain separated.
The ISP can provide IPv4 in a flexible, on-demand way, as well as
manage the native IPv6 network without the influence of IPv4-over-
IPv6 requirements. And it would also be easy to achieve future
adjustment of IPv4 address pool.
The costs of lightweight 4over6 for achieving all these benefits are
lower IPv4 address utilization ratio and extra signaling behavior.
The address multiplexing manner of port restricted address is
relatively more static than the CGN manner. This may cause the port
randomization algorithm more predictable. There are solutions which
increase the prediction difficulty at the cost of more sophisticated
port rule mapping [I-D.bsd-softwire-stateless-port-index-analysis].
And dual-stack lite doesn't require address and port allocation
between concentrator and initiators. When compared to stateless
solutions, lightweight 4over6 still keeps per-user states rather than
becoming purely stateless.
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10. References
[I-D.bajko-pripaddrassign]
Bajko, G., Savolainen, T., Boucadair, M., and P. Levis,
"Port Restricted IP Address Assignment",
draft-bajko-pripaddrassign-03 (work in progress),
September 2010.
[I-D.bsd-softwire-stateless-port-index-analysis]
Boucadair, M., Skoberne, N., and W. Dec, "Analysis of Port
Indexing Algorithms",
draft-bsd-softwire-stateless-port-index-analysis-00 (work
in progress), September 2011.
[I-D.cui-softwire-dhcp-over-tunnel]
Cui, Y., Wu, P., and J. Wu, "DHCPv4 Behavior over IP-IP
tunnel", draft-cui-softwire-dhcp-over-tunnel-01 (work in
progress), July 2011.
[I-D.cui-softwire-host-4over6]
Cui, Y., Wu, J., Wu, P., Metz, C., Vautrin, O., and Y.
Lee, "Public IPv4 over Access IPv6 Network",
draft-cui-softwire-host-4over6-06 (work in progress),
July 2011.
[I-D.murakami-softwire-4rd]
Murakami, T., Troan, O., and S. Matsushima, "IPv4 Residual
Deployment on IPv6 infrastructure - protocol
specification", draft-murakami-softwire-4rd-01 (work in
progress), September 2011.
[I-D.sun-v6ops-laft6]
Sun, Q. and C. Xie, "LAFT6: Lightweight address family
transition for IPv6", draft-sun-v6ops-laft6-01 (work in
progress), March 2011.
[I-D.tsou-pcp-natcoord]
Zhou, C., ZOU), T., Deng, X., Boucadair, M., and Q. Sun,
"Using PCP To Coordinate Between the CGN and Home Gateway
Via Port Allocation", draft-tsou-pcp-natcoord-03 (work in
progress), July 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
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Authors' Addresses
Yong Cui
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-62603059
Email: yong@csnet1.cs.tsinghua.edu.cn
Jianping Wu
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-62785983
Email: jianping@cernet.edu.cn
Peng Wu
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-62785822
Email: weapon@csnet1.cs.tsinghua.edu.cn
Qiong Sun
China Telecom
Room 708, No.118, Xizhimennei Street
Beijing 100035
P.R.China
Phone: +86-10-58552936>
Email: sunqiong@ctbri.com.cn
Chongfeng Xie
China Telecom
Room 708, No.118, Xizhimennei Street
Beijing 100035
P.R.China
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Phone: +86-10-58552116>
Email: xiechf@ctbri.com.cn
Cathy Zhou
Huawei Technologies
Section B, Huawei Industrial Base, Bantian Longgang
Shenzhen 518129
P.R.China
Phone: +86-10-58552116>
Email: cathyzhou@huawei.com
Yiu L. Lee
Comcast
One Comcast Center
Philadelphia, PA 19103
USA
Email: yiu_lee@cable.comcast.com
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