Internet Engineering Task Force X.Deng
Internet Draft M.Boucadair
Intended status: Informational France Telecom
Expires: January 4, 2013 X.Wang
BUPT
July 3, 2012
Using PCP to update dynamic DNS
draft-deng-pcp-ddns-00.txt
Abstract
This document focuses on the problems encountered when using dynamic
DNS in address sharing contexts (e.g., DS-Lite, NAT64, A+P)during
IPv6 transition. Issues, possible solutions and preliminary
implementation and validation of one of the solutions are documented
in this memo.
Status of this Memo
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This Internet-Draft will expire on January 4, 2013.
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Table of Contents
1. Problem statement ........................................... 2
2. Solution Space .............................................. 3
2.1. Locate a service port................................... 3
2.2. Detect the changes ..................................... 4
3. Implementation & Validation ................................. 7
4. References .................................................. 8
4.1. Normative References.................................... 8
4.2. Informative References.................................. 8
5. Authors' Addresses .......................................... 9
1. Problem statement
Dynamic DNS (DDNS) is a widely deployed service to facilitate hosting
servers (e.g., to host webcam and http server) at home premises.
There are a number of providers who offer a DDNS service, working in
a client and server mode. DDNS clients are generally implemented in
the user's router or computer, which once detects changes to its IP
address it automatically sends an update message to the DDNS server.
The communication between the client and the server is not
standardised, varying from one provider to another, although a few
standard web-based methods of updating have emerged over time.
When the network architecture evolves towards an IPv4 sharing
architecture during IPv6 transition, the DDNS Client will have to not
only inform the IP address updates if any, but also to notify the
changes of external port on which the service is listening, because a
well know port numbers, e.g. port 80 will no longer be available to
every web server. It will also require the ability to configuring
corresponding port forwarding on CGN devices, so that incoming
communications initiated from outside can be routed to the
appropriate server behind the CGN.
This document focuses on the problems encountered when using dynamic
DNS in address sharing contexts (e.g., DS-Lite, NAT64, A+P). Below
are listed the main challenges to us:
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(1)
The DDNS service MUST be able to maintain an alternative port
number instead of the default port number.
(2)
Appropriate means to instantiate port mapping in the address
sharing device MUST be supported.
(3)
DDNS client MUST be triggered by the change of the external IP
address and the port number. Concretely, upon change of the external
IP address, the DDNS client MUST refresh the DNS records otherwise
the server won't be reachable from outside. This issue is event
exacerbated in the DS-Lite context because no IPv4 address is
assigned to the CPE.
This document describes solutions to counter the issues listed above
in the particular case of DS-Lite.
Note DDNS may be considered as an implementation of the Rendez-vous
service mentioned in [I-D.ietf-pcp-base].
"After creating a mapping for incoming connections, it is necessary
to inform remote computers about the IP address, protocol, and port
for the incoming connection. This is usually done in an application-
specific manner. For example, a computer game might use a rendezvous
server specific to that game (or specific to that game developer), a
SIP phone would use a SIP proxy, and a client using DNS-Based Service
Discovery [I-D.cheshire-dnsext-dns-sd] would use DNS Update
[RFC2136][RFC3007]. PCP does not provide this rendezvous function.
The rendezvous function may support IPv4, IPv6, or both. Depending
on that support and the application's support of IPv4 or IPv6, the
PCP client may need an IPv4 mapping, an IPv6 mapping, or both."
Dynamic Updates in the standard Domain Name System (DNS UPDATE)
(RFC2136) is out of scope of this memo.
2. Solution Space
2.1. Locate a service port
At least two solutions can be used to associate a port number with a
service identified:
(1)
Use service URIs (e.g., FTP, SIP, HTTP) which embed an explicit
port number. Indeed, Uniform Resource Identifier (URI) defined in
[RFC3986] allows to carry port number in the syntax (e.g.,
mydomain.example:15687)
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(2)
Use SRV records. Unfortunately, the majority of browsers do not
support this record type.
DDNS client and server are to be updated so that an alternative port
number is also signalled and stored by the server. Requesting remote
hosts will be then notified with the IP address and port number to
use to reach the server.
2.2. Detect the changes
+-----------------+
| DDNS Server |
| |
+-----------------+
^
|
|3. DDNS updates
| (if any)
|
+-----------------+ +-----------------+
|DDNS Client |1. PCP MAP request | CGN/PCP Server |
|PCP Client/IWF ON|------------------->| (PCP mapping for 80:8080 +------+
|CPE or |2. PCP MAP response | port forwarding)|<---------|Client|
|the host itself |<-------------------| | | |
| |3. DDNS updates | | +------+
| | (if any) | |
| |------------------->| |
+-----------------+ +-----------------+
Figure 1 : Flow chat
First of all, PCP MUST be used to install the appropriate mapping in
the CGN so that incoming packets can be delivered to the appropriate
server.
In a network described in figure 1, DDNS Client/ PCP Client can
either be running on a Customer Premise Equipment (CPE) or be running
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on the host that is hosting some services, itself. There are
possible ways to address the problems stated in section 1.
(1)
If the DDNS client is enabled, the host issues periodically (e.g.,
1h) PCP MAP requests (e.g., messages 1 and 2 in Figure 1) with short
lifetime (e.g., 30s) for the purpose of enquiring external IP address
and setting. If the purpose is to detect any change of external port,
the host must issues a PCP mapping to install a mapping for the
internal server. Upon change of the external IP address, the DDNS
client updates the records (e.g., message 3 in Figure 1).
(2)
If the DDNS client is enabled, it checks the local mapping table
maintained by the PCP client. This process is repeated periodically
(e.g., 5mn, 30mn, 1h). If there is no PCP mapping caused by PCP
client losing states for example, it issues a PCP MAP request (e.g.,
messages 1 and 2 in Figure 1) for the purpose of enquiring external
IP address and setting up port forwarding mappings for incoming
connections. Upon change of the external IP address, the DDNS client
updates the records in the DDNS server, e.g., message 3 in Figure 1.
(3)If the DDNS client is enabled, the A/AAAA records of DNS (which
could be normal one as using on the Internet now) were set to point
the DDNS Server. DDNS is responsible for the translation between
public IPv4 address (address of DDNS) with specific port (E.g. web
with 80 port) and public IPv4 address (outside IPv4 address and port
number of mappings). Show as Figure 2.
(4)If a user of another client outside DS-Lite network wants to
access a server behind AFTR, the role of DDNS started to become
important. Before that the following mappings should had been
configured well:
a. PCP mappings: private IPv4 address: port number <--> public
IPv4 address: port number
b. DDNS mappings: public IPv4 address: port number <--> domain
name
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c. DNS Resolution: A/AAAA Records (point to the DDNS server) <-->
domain name
Customer DDNS AFTR CPE Visitor
| DNS request | public |encapsulated | |
|------------>| address: port |private | |
| |--------------->|address: port| |
| | |------------>| IPv4 request |
| | response |-------------->|
|<------------|----------------|-------------|---------------|
| | | | |
Figure 2 : Time Sequence Chart
(5) A domain resolution request is sent from host of customer who
asking service. The request is sent to the DNS server. And DNS server
would return a response with A/AAAA records pointing to the DDNS
server. If the request is sent to the DDNS directly, it would
redirect the request to the pointed IPv4 address and port number
which has been configured in the mappings.
(6) After redirection the request is routed to the AFTR. AFTR would
translate it from public IPv4 address and port number into private
IPv4 address and port. The request finished AFTR translation and is
encapsulated into a IPv4-in-IPv6 package until CPE.
(7) At last the request would be decapsulated to an IPv4 package and
is sent to the service provider. And the response would return to the
customer as requested routine. The whole communication process is
finished successfully.
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3. Implementation & Validation
So far the topology of network was implemented as Figure 1. Based on
the DS-Lite environment some new roles added into it such as DDNS. It
could be implemented by Apache or other applications which has
virtual host functions. The DDNS need to be configured as a virtual
host and redirect corresponding request to the pointed IPv4 address
and port number. It could be validated as Figure 3 shows.
---------------- ---------- ----------- ---------- ---------
|Service Server| | PCP | | CGN& | | DDNS | |User's |
| DDNS client |---| Client|----| PCP |---| Server |---|Host |
| | | | | Server | | | | |
---------------- ---------- ----------- ---------- ---------
Service provider B4 AFTR DDNS Visitor
Figure 3 : Implementation Chart
Service provider: Web server was deployed in the DS-Lite network
environment. It just has private IPv4 address and with a mapping in
AFTR to the public network. The server may offer Web, FTP, SIP
service and so on. And these services may not be set as their
specific port. (this also is the reason why introducing DDNS into DS-
Lite environment)
B4 (CPE): An endpoint of IPv4-in-v6 tunnel, and PCP client also
runs on it. A package from Service Server is encapsulated into a
IPv4-in-v6 one and is sent to the AFTR. A package from AFTR will be
decapsulated to a normal IPv4 package and to their destination.
AFTR: Responsible for mappings between internal IPv4 Address: port
and external IPv4 address: port. It maintains a table to restore
these data to keep state of every mapping.
DDNS: Maintaining mappings between domain name and external IPv4
address: port. If a DNS request was sent to it, DDNS server could
resolve it to the AFTR which contains that IPv4 address and port
number.
Visitor: Some users who need to access service on the Service
Server. They send service request needed to resolve domain name. And
the response would returned to their hosts as the ways of request
reached to the Service Server.
From the view of visitor, the location of service server is on DDNS,
just like a virtual host. It at least has three advantages. Firstly,
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hackers and other attackers couldn't reach the real host and do
something bad. The security is assured. Secondly, many domain name or
space ISPs also provide service of domain and port mapping. However,
some companies may use iframe or 301 redirection technology. Those
means could lead to lower speed and affect PR weights to the search
engine. Click-through rate and visits was 'stolen'. That could not be
introduced into Carrier Scale Network. Hence, generation of DDNS has
its unique meaning. Thirdly, DDNS solution could solve the problems
of IP address + port mapping almost perfectly. Under DS-Lite network
environment normal DNS resolution couldn't point a domain name to a
IP address and a port. Because of designing defect of traditional DNS
protocol a DNS request just could be resolve to be a A/AAAA record
(the services have their own specific port. Such as web is 80 and ftp
is 21, etc.). So DDNS as a supplementary was introduced into DS-Lite
to play a role of mapping between domain name and IP address and port
number.
4. References
4.1. Normative References
[RFC2136]
P. Vixie, et. al." Dynamic Updates in the Domain Name
System (DNS UPDATE)", April 1997.
[RFC3007]
B. Wellington, " Secure Domain Name System (DNS) Dynamic
Update", November 2000.
[RFC3986]
T. Berners-Lee, et. al. " Uniform Resource Identifier (URI):
Generic Syntax", January 2005.
4.2. Informative References
[I-D.ietf-pcp-base]
D. Wing, et. al. " Port Control Protocol (PCP)", June 5,
2012.
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5. Authors' Addresses
Xiaohong Deng
France Telecom
Rennes,35000 France
Email: dxhbupt@gmail.com
Mohamed BOUCADAIR
France Telecom
Rennes,35000 France
Email: mohamed.boucadair@orange.com
Xu Wang
Beijing University of Posts and Telecommunications, China
Email: cngesaint@gmail.com
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