v6ops C. Xie
Internet-Draft China Telecom
Intended status: Informational X. Li
Expires: September 13, 2012 Tsinghua University
J. Qin
Consultant
M. Chen
FreeBit
A. Durand
Juniper Networks
March 12, 2012
Practice of IPv4/IPv6 transition system for data center
draft-sunq-v6ops-contents-transition-03
Abstract
This document describes deployment practice of IPv4/IPv6 translation
technologies for data center transition, aiming at rapidly increasing
the amount of IPv6 accessible contents for users from IPv6 Internet
while preserving the continuity of IPv4 service delivery. System
based on this design has been deployed in production network to
provide transition service for several ICP websites.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Motivations . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Transition As A Service . . . . . . . . . . . . . . . . . 5
3.2. Guiding the traffic to IPv6 network . . . . . . . . . . . 6
4. Deployment practice one: Communication from IPv6 users to
IPv4 server . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Deployment scenario . . . . . . . . . . . . . . . . . . . 6
4.2. Mapping and Addressing . . . . . . . . . . . . . . . . . . 7
4.3. DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.4. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 8
4.5. Logging . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.6. Geographically aware services . . . . . . . . . . . . . . 9
4.7. ALG issues . . . . . . . . . . . . . . . . . . . . . . . . 9
4.8. High Availability . . . . . . . . . . . . . . . . . . . . 10
4.9. Security . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.10. Deployment practices . . . . . . . . . . . . . . . . . . . 10
5. Deployment practice two: communications from IPv4 users to
IPv6 server . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Deployment scenario . . . . . . . . . . . . . . . . . . . 11
5.2. Mapping and Addressing . . . . . . . . . . . . . . . . . . 11
5.3. DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.4. Logging . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.5. Geographically aware services . . . . . . . . . . . . . . 12
5.6. ALG issues . . . . . . . . . . . . . . . . . . . . . . . . 12
5.7. High Availability . . . . . . . . . . . . . . . . . . . . 12
5.8. Security . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.9. Deployment practices . . . . . . . . . . . . . . . . . . . 13
6. Additional Author List . . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
Facing the pressure of IPv4 address shortage, the operators may like
to provide services through IPv6 by upgrade their IP infrastructure
to support IPv6. As part of the Infrastructure, Data center (in
short, IDC) is the main faculty to house service system that provides
services and contents. It is obvious that data center also plays an
important role in IPv6 transition in accordance with the transition
of IP network. Dual-stack is the basic transition strategy for most
data centers, as well as IP transport network. However, in our
practices, we found that dual-stack alone is not enough to meet the
transition demand of ICPs(in short, ICP) in data centers. The reason
behind this is that providing IPv6 services requires the service
software of ICP, i.e., website system, database system, supporting
system, etc., should be IPv6-aware and can deal with IPv6-related
information. Upgrading the service system to support IPv6 is
technological-complicated and financially costly, especially for some
small and medium-sized ICPs, which is the main reason that the IPv6
transition on the ICP sides moves even more slowly than the readiness
of operators' IP network. The lack of IPv6-reachable contents
becomes one of the main obstacles. On the other hand, some
progressive ICPs who are willing to setup an IPv6-only system also
would like to offer IPv4 continuity for end-users.
Under such circumstances, we propose to deploy IDC transition system
in data center, aiming at aiding CP/SP to provide IPv6 services
rapidly and smoothly. Another purpose of our approach is to increase
the amount of IPv6 accessible contents for users from IPv6 Internet.
It can also keep the IPv4 continuity for IPv6-only contents.
This document describes our current experiences on two deployment
models for the transition of data center based on the approaches
specified by IETF (e.g., NAT64 [RFC6146], Dual-Stack [RFC4213],
IVI[RFC6219], etc.), targeting different use cases or conditions.
Based on these models, an IDC transition system was designed and
developed by China Telecom to provide transition services to ICPs in
data centers. Some issues and considerations were also identified
from the actual deployment.
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. Motivations
As mentioned above, IDC's transition is closely related to the IPv6
service provisioning of ICPs. There have been statements from
several popular ICPs that they have turned on IPv6 (no matter by
which means), which do have a beneficial effect on encouraging end
users' transition to IPv6. However, given the operational cost, it
is still difficult for most ICPs (especially the great many ones of
small-to- medium size) to immediately make their publically-facing
services accessible through both IPv4 and IPv6 natively. It will
involve a lot of workload for upgrading numerous application systems
and the supporting systems in ICPs. On the other hand, from the
users' perspective, the IPv6 reachability of resources required for
their daily lives is one of the foremost concerns when making the
decision on whether or not to access Internet using IPv6. It is a
chicken or egg dilemma, but the two perspectives are interdependent.
If the transition of one side passes the point of inflexion, the
other side will be speeded up after. So, more efforts are needed to
encourage the IPv6 adoption and reach the point.
Moreover, some progressive ICPs are willing to maintain a separated
IPv6-only system, which will lower the risk of the potential impact
on their existing wildly used IPv4 system in the early phase.
Besides, single-stack system is also easy for operation, management
and troubleshooting. There are no duplicated policies need to be
applied, including e.g. ACL control, accounting, authentication,
etc. In this case, it is also the requirement to offer IPv4
continuity to IPv6-only contents.
Therefore, the transition system provided by operators in data
centers will not only help promote ICP transition in a step-by-step
way, but also break out the chicken or egg dilemma for the whole IPv6
industry.
3.1. Transition As A Service
In China Telecom, we have deployed a transition platform in our IDC
network. It can be regarded as transition services offered by the
operators, to small-to-medium size ICPs (e.g., those who rent servers
from the operators).
The ICPs can choose to take different approaches according to their
scenarios and business strategies. For the conservative ones, the
IPv4 services can be still offered natively, and the IPv6 services
can be offered by the stateful IPv4/IPv6 translation [RFC6146].
While for progressive ones and newly incomers, the stateless IVI
[RFC6219], [RFC6052] can be employed to offer native IPv6 services
reachable via IPv4.
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3.2. Guiding the traffic to IPv6 network
IPv4 address shortage has driven some network providers began to run
IPv6 in part or the whole network. However, even if IPv6 is ready in
the IP network, most ICPs in IDC have not been ready to provide IPv6
services. As a result, almost all the traffic is still IPv4-based,
which makes the IPv6 network nearly empty. With this in mind, IPv4/
IPv6 translation system deployed in IDC can translate the IPv4
packets sourced from the existing servers into IPv6 packets, and
forward them into IPv6 network, which is equal to move the traffic
from IPv4 network to IPv6 network. and encourage the customers to use
IPv6 from the beginning. Furthermore, only translation will be
performed on the edge of the network and it is independent of user-
side transition mechanisms.
4. Deployment practice one: Communication from IPv6 users to IPv4
server
4.1. Deployment scenario
We have deployed transition service gateway in the exit of our IDCs.
It is a shared platform which can serve multiple servers
simultaneously. It can be integrated with existing network element
of our IDC, e.g. egress router, load balancer, etc., or can be
deployed as a new standalone device. The integrated deployment
scenario would have little impact on existing network topology;
however, it is highly coupled with existing devices. The standalone
deployment scenario would be easier to implement on existing network
incrementally. However, it will result in extra cost for new
devices.
The egress router of our IDC is IPv6-reachable, however, either the
content servers or the whole IDC infrastructure have been upgraded to
IPv6 directly. With the help of transition gateway, we can provide
IPv6 reachable content to customers in a quick manner. Our
deployment model is depicted in the following picture.
+----------------+ +---------------+ +--------------+
| Data Center | | Transition | | IPv6 |
| | --- | Gateway | --- | Internet |
| +--------+ | +---------------+ +--------------+
| | IPv4 | |
| | Server | | +--------------+
| +--------+ | ------------------------ | IPv4 |
| | | Internet |
+----------------+ +--------------+
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Figure 1: Deployment Model 1
In this deployment model, the Stateful NAT64 is performed to
translate IPv6 packets to IPv4 and vice versa. The guidance in
[RFC6146] should be followed. The communications are initiated from
the IPv6 side. When an IPv6 packet arrives, a lookup of the mapping
table will be carried out to get the IPv4 address used for the
translation. If there is no one matched, a new entry will be
created.
The server-side deployment model is independent of user-side
transition When a dual-stack user gets both A and AAAA records for a
remote server, it will be encouraged to reach IPv4 content via IPv6
connectivity through the only NAT64 gateway along the path. So even
if there are some other CGNs deployed in the customer-side, IPv6
traffic will be forwarded in a traditional way. Therefore, there
will be no double-translation problems around here.
Up to now, there are 8 sites including the official website of China
Telecom have been upgrading to IPv6 with this mechanism. More than
15 thousands different IPv6 users ever accessing the above eight ICPs
through the transition box totally, with 4000 to 6000 active users
every day. www.voc.com.cn is the most popular one accessed by more
than 4000 IPv6 users daily, and www.chinatelecom.com.cn (the official
website of china telecom) has amounts of access from 1200 IPv6 users
on average every day.
4.2. Mapping and Addressing
The Stateful NAT64 can support the following two mapping modes:
o 1:1, one IPv6 address is mapped to one IPv4 address (exclusively
for given lifetime);
o N:1, each of the IPv4 addresses (i.e. IPv4 address pool) will be
shared by multiple IPv6 users from Internet.
To save global IPv4 addresses which has become scarce resource,
private blocks, for instance 10.0.0.0/8 may be used for the Stateful
NAT64. This private address block can only be seen within the IDC
network.
Considering the scale of traffic in the foreseeable future, the 1:1
Mapping Mode with private blocks (one IPv6 address mapped to one
private IPv4 address within 10.0.0.0/8) is selected as the default mode
for the Stateful NAT64. In this mode, there is only address-layer
mapping and no TCP/UDP session maintenance anymore. By this mean,
the efficiency of stateful operations could be improved and the
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problems introduced by the address sharing could be alleviated (for
example, the burden of logging will be reduced in this mode).
However, there may be conflicts if the same private space is used
internally for the interconnection of servers (e.g. multiple servers
for load balancing). In this case, N:1 mode with public blocks can
be used. In order to reduce state management burden in N:1 stateful
NAT64 gateway as well as logging system, a bulk of ports can be
allocated for each subscriber. In this port-set based mapping mode,
one IPv6 address will be mapped to the same IPv4 address and a given
port-set.
In addition, an IPv6 prefix is used to serve the IPv4 servers in the
IDC, and the route of the prefix has been advertised to the IPv6
Internet. The IPv4 address of the server can be embedded in the IPv6
prefix following the algorithm specified in [RFC6052].
4.3. DNS
To make sure the addresses of servers can be retrieved by IPv6 users
before initiating sessions, the AAAA records which formed through
IPv4-translated addresses have been added directly on the domain's
authoritative DNS, or upgrade authoritative DNS to support DNS64. In
this way, the AAAA records under one domain name could be retrieved
by IPv6 users around the world.
Please note that if the authoritative DNS of given ICPs' domain names
are maintained by some third-party DNS Providers but not by
themselves or the operator from whom this transition service (i.e.
the deployment model of Stateful NAT64 discussed herein) is
purchased, the ICPs must make sure the authoritative AAAA records can
be added.
4.4. Fragmentation
Basically, the processing of packets carrying fragments follows the
guidance specified in [RFC6145] and [RFC6146] with exceptions that
fragmented IPv4/IPv6 packets will be firstly reassembled to an
integrated packet before doing packet translation and so on.
4.5. Logging
The logging is essential for tracing back specific users in stateful
NAT64. In 1:1 mode, only per-user logging events need to be recorded
as {IPv6 address, IPv4 address, timestamp}. For N:1 mode, in order
to reduce the number of sessions need to be logged, we adopt port-set
based mechanism to assign a bulk of ports to each subscriber.
Therefore, one subscriber will only create one corresponding log
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report, e.g. {IPv4 address, IPv6 address, port-set, timestamp}.
4.6. Geographically aware services
Since converted IPv4 address would not represent any geographical
feature anymore, applications that assume such geographic information
may not work as intended.
Two solutions were designed and implemented, one is to maintain the
above logging information in geographic server as well, and offer an
open API to ICPs to retrieve its original IPv6 address when
necessary. It will have little impact on NAT64 gateway since there
is no application-layer procedure. However, due to the transmission
and computational latency in geographic servers, it is more suitable
for ICPs to retrieve IPv6 users' source address offline. Another way
is to embed user's source IPv6 address in x-forward field of user's
request when it traverses NAT64 gateway. This involves application-
layer process which will bring extra burden on NAT64 gateway. So
only for ICPs who really need online users' source address will be
offered with this additional service.
4.7. ALG issues
Since the types of applications are relatively limited due to the
deployment policy, it would be easier to solve the ALG issue compared
to client-side deployment. For example, Web-based ICPs might be
introduced in the first stage, and so specific ALGs can be applied
accordingly.
Since video traffic constitutes a great portion of the whole Internet
traffic, we have implemented HTTP AGLs for video traffic in
particular.
In our test for TOP100 Websites in China, there are basically three
types of HTTP ALGs for video traffic.
HTTP/1.1 302 Found: This is a common way of performing a
redirection. Usually, IPv4 address literals for redirected server
will be embedded in Location header.
HTTP/1.1 301 Moved Permanently: This is also a redirect way
indicating the requested resource has been assigned a new
permanent place, and the IPv4 address literals for redirected
server will also be embedded in Location header.
HTTP/1.1 200 ok: This code means the request has succeeded.
However, some ICPs will still embed the IPv4 address literals to
indicate the redirected server in the following communication, and
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they will use a great variety of keywords. For example,
www.sina.com.cn uses the keyword "CDATA[http://" followed by a
list of IPv4 addresses, and v.6.cn use "watchip" as its keyword.
Since the first two types occupy the great majority of existing ALGs
for HTTP-based videos traffic, we have implemented the ALG for the
first two cases to synchronize an IPv4-translated address if the
server of the embedded IPv4 address is located within the NAT64
region.
4.8. High Availability
In general, there are two mechanisms to achieve high reliability,
i.e. cold-standby and hot-standby. In cold-standby mode, the NAT64
states are not replicated from the Primary NAT64 gateway to the
Backup NAT64 gateway. When the Primary NAT64 gateway fails, all the
existing established sessions will be flushed out. The hosts are
required to re-establish sessions with the external hosts. Another
high availability option is the hot standby mode. In this mode the
NAT64 gateway keeps established sessions while failover happens. The
1:1 mapping mode will greatly reduce the amount of sessions needed to
be replicated on-the-fly from the Primary NAT64 gateway to the Backup
gateway. Another option is to deploy an Anycast NAT64 prefix. This
is similar to cold-standby that NAT64 states are not replicated
between Primary gateway and Backup gateway, except that the heartbeat
line is not needed anymore.
4.9. Security
The security issues and considerations discussed in [RFC6146] apply
to the deployment model described in this document. However, when
deploying stateful NAT64 in server side, it is hard to apply source-
based filtering policy. As a result, we have introduced alarming
mechanism to report the current status of state-consuming speed in
NAT64 gateway.
Besides, both 1:1 mapping mode and port-set based N:1 mapping mode
can guarantee that one IPv6 source address will be mapped to a single
IPv4 address. Therefore, the ICP can identify a single subscriber
either by IPv4 source address in 1:1 mapping, or IPv4 source address
plus port-set in N:1 mapping.
4.10. Deployment practices
Up to now, there are 8 sites including the official website of China
Telecom have been upgrading to IPv6 with this mechanism. More than15
thousands different IPv6 users ever accessing the above eight Content
Providers through the transition box totally, with 4000 to 6000
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active users every day. www.voc.com.cn is the most popular one
accessed by more than 4000 IPv6 users daily, and
www.chinatelecom.com.cn (the official website of china telecom) has
amounts of access from 1200 IPv6 users on average every day.
5. Deployment practice two: communications from IPv4 users to IPv6
server
5.1. Deployment scenario
Considering in the foreseeable future, IPv6 will be a widely accepted
protocol in the Internet, some ICPs, especially newcomers, will setup
IPv6-only servers, to reduce the operation and maintenance
complexity. When the server in question itself is IPv6-
capable,communications initiated from IPv6 users will not encounter
any transition problem. What we are concerned is the communications
initiated from IPv4 users. To mitigate this problem, IPv4/IPv6
translation is utilized in the IDC that the server resides. In this
scenario, the IPv4 node will firstly get A/AAAA records of the server
from DNS, and then the communication will follow the path to NAT64
Gateway. When an IPv4 packet arrives at NAT64 Gateway, it would be
translated to an IPv6 packet based on stateless 1:1 mapping algorithm
[RFC6219].
+----------------+ +------------+ +--------------+
| Data Center | | Transition | | IPv4 |
| | --- | Gateway | --- | Internet |
| +--------+ | +------------+ +--------------+
| | IPv6 | |
| | Server | | +--------------+
| +--------+ | -------------------- | IPv6 |
| | | Internet |
+----------------+ +--------------+
Figure 2: Deployment Model2
5.2. Mapping and Addressing
To eliminate the state management burden, we adopted stateless
transition gateway to do the Interworking between IPv4 Internet and
IPv6-only server within IDC, IPv6-only server should be configured
with an IPv4-translatable address. Then both source address and
destination address are applied with 1:1 mapping to keep the
simplicity and transparency.
In addition, an IPv4 address within the range of a given IPv4 prefix
is used to represent the IPv6 server, and the route of the IPv4
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prefix has been advertised to the IPv4 Internet. An IPv6 prefix will
be assigned to the IDC to represent the whole IPv4 Internet, when
IPv4 packet traverse the transition gateway, IPv6 addresses, e.g.,
source address and destination address, will be formed by combine the
IPv4 address with a IPv6 prefix following the algorithm specified in
[RFC6052]. In this way, the server can be reachable from IPv4
Internet without mapping states in transition gateway.
5.3. DNS
To make sure that addresses of servers can be retrieved by IPv4 users
before initiating sessions, the A records which are extracted from
IPv4-translated addresses should be added directly on the domain's
authoritative DNS, or upgrade authoritative DNS to support DNS64.
Other considerations are actually the same with Section 4.
5.4. Logging
There is no logging issue in stateless transition solution.
5.5. Geographically aware services
When a ICP gets an IPv4-converted IPv6 addresses with a pre-defined
Prefix, it should extract the embedded IPv4 address which would
reflects its original geographical information.
5.6. ALG issues
ALG issues would be the same with section 4.6.
5.7. High Availability
Since there is no state maintained in the transition gateway, state
replication or re-establishment encountered in the HA of the first
deployment model will not exist in the second one.
5.8. Security
IPv4/IPv6 translators which can be modeled as special routers, are
subject to the same risks, and can implement the same mitigations.
(The discussion of generic threats to routers and their mitigations
is beyond the scope of this document.) There is, however, a
particular risk that often happens in IPv4 Internet: address
spoofing.
An attacker could use a faked IPv4 address as the source address of
malicious packets. After translation, the packets will appear as
IPv6 packets from the specified source, and the attacker may be hard
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to track. If left without mitigation, the attack would allow
malicious IPv4 nodes to spoof arbitrary IPv4 addresses.
The mitigation is to implement reverse path checks and to verify
throughout the network that packets are coming from an authorized
location.
5.9. Deployment practices
The following IPv6-only websites has been setup to provide native
IPV6 service to IPv6 users, all of them are hosted in a dual-stack
IDC.
http://iptv.bupt.edu.cn
http://www.mayan.cn
http://www.ivi.buptnet.edu.cn
In order to accommodate the access of great volume of existing IPv4-
only users, stateless transition gateway was deployed to provide
translation in the exit of the IDC. Currently, the peak of the
traffic is around 900Mbps.
6. Additional Author List
Qiong Sun
China Telecom
Room 708 No.118, Xizhimenneidajie
Beijing, 100035
P.R.China
Phone: +86 10 5855 2923
Email: sunqiong@ctbri.com.cn
Qian Liu
China Telecom
No.359 Wuyi Rd.,
Changsha, Hunan 410011
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P.R.China
Phone: +86 731 8226 0127
Email: 18973133999@189.cn
Qin Zhao
BUPT
Beijing 100876
P.R.China
Phone: +86 138 1127 1524
Email: zhaoqin@bupt.edu.cn
7. IANA Considerations
This document includes no request to IANA.
8. Acknowledgements
The authors would like to thank Fred Baker, Joel Jaeggli, Erik Kline,
Randy Bush for their comments and feedback.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
[RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation", RFC 6144, April 2011.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
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Algorithm", RFC 6145, April 2011.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6154] Leiba, B. and J. Nicolson, "IMAP LIST Extension for
Special-Use Mailboxes", RFC 6154, March 2011.
[RFC6219] Li, X., Bao, C., Chen, M., Zhang, H., and J. Wu, "The
China Education and Research Network (CERNET) IVI
Translation Design and Deployment for the IPv4/IPv6
Coexistence and Transition", RFC 6219, May 2011.
9.2. Informative References
[I-D.wing-behave-http-ip-address-literals]
Wing, D., "Coping with IP Address Literals in HTTP URIs
with IPv6/IPv4 Translators",
draft-wing-behave-http-ip-address-literals-02 (work in
progress), March 2010.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
Authors' Addresses
Chongfeng Xie
China Telecom
Room 708 No.118, Xizhimenneidajie
Beijing, 100035
P.R.China
Phone: +86 10 5855 2116
Email: xiechf@ctbri.com.cn
Xing Li
Tsinghua University
Room 225, Main Building
Beijing 100084
P.R.China
Phone: +86 10 6278 5983
Email: xing@cernet.edu.cn
Xie, et al. Expires September 13, 2012 [Page 15]
Internet-Draft Contents Transition March 2012
Jacni Qin
Consultant
Shanghai,
China
Phone: +86 1391 861 9913
Email: jacniq@gmail.com
Maoke Chen
FreeBit Co., Ltd.
13F E-space Tower, Maruyama-cho 3-6
Shibuya-ku, Tokyo 150-0044
Japan
Email: fibrib@gmail.com
Alain Durand
Juniper Networks
1194 North Mathilda Avenue
Sunnyvale, CA 94089-1206
USA
EMail: adurand@juniper.net
Xie, et al. Expires September 13, 2012 [Page 16]