INTERNET DRAFT Seungyun Lee
NGTRANS Working Group Myung-Ki Shin
Expires: October 2002 Yong-Jin Kim
ETRI
Erik Nordmark
Alain Durand
Sun Microsystems
April 2002
Dual Stack Hosts using "Bump-in-the-API" (BIA)
<draft-ietf-ngtrans-bia-04.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
Internet Drafts are working documents of the Internet Engineering Task
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It is inappropriate to use Internet Drafts as reference material or to
cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
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Abstract
This document specifies a mechanism of dual stack hosts using a
technique called "Bump-in-the-API"(BIA) which allows for the hosts to
communicate with other IPv6 hosts using existing IPv4 applications. The
goal of this mechanism is the same as that of the Bump-in-the-stack
mechanism [BIS], but this mechanism provides the translation method
between the IPv4 APIs and IPv6 APIs. Thus, the goal is simply achieved
without IP header translation.
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Table of Contents:
1. Introduction ................................................. 2
2. Applicability and Disclaimer ................................. 3
2.1 Applicability ............................................ 3
2.2 Disclaimer ............................................... 3
3. Dual Stack Host Architecture using BIA ....................... 4
3.1 Function Mapper .......................................... 4
3.2 Name Resolver ............................................ 4
3.3 Address Mapper ........................................... 5
4. Behavior Example ............................................. 6
4.1 Originator Behavior ...................................... 6
4.2 Recipient Behavior ....................................... 8
5. Considerations .............................................. 9
5.1 Socket API Conversion .................................... 9
5.2 ICMP Messages Handling ................................... 10
5.3 IPv4 Address Pool and Mapping Table ...................... 10
5.4 Internally Assigned IPv4 Addresses ....................... 10
5.5 Mis-match between DNS Result and Peer Application version 10
5.6 Implementation Issues .................................... 11
6. Limitations .................................................. 11
7. Security Considerations ...................................... 11
8. Acknowledgments .............................................. 12
9. References ................................................... 12
Appendix : API list intercepted by BIA .......................... 13
Authors Addresses ............................................... 14
1. Introduction
RFC2767 [BIS] specifies a host translation mechanism using a technique
called "Bump-in-the-Stack". It translates IPv4 into IPv6, and vice versa
using the IP conversion mechanism defined in [SIIT]. BIS allows hosts to
communicate with other IPv6 hosts using existing IPv4 applications.
However, this approach is to use an API translator which is inserted
between TCP/IP module and network card driver, so that it has the same
limitations as the [SIIT] based IP header translation methods. In
addition, its implementation is dependent upon the network interface
driver.
This document specifies a new mechanism of dual stack hosts called
Bump-in-the-API(BIA) technique. The BIA technique inserts an API
translator between the socket API module and the TCP/IP module in the
dual stack hosts, so that it translates the IPv4 socket API function
into IPv6 socket API function and vice versa. With this mechanism, the
translation can be simplified without IP header translation.
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Using BIA, the dual stack host assumes that there exists both
TCP(UDP)/IPv4 and TCP(UDP)/IPv6 stacks on the hosts.
When IPv4 applications on the dual stack communicate with other IPv6
hosts, the API translator detects the socket API functions from IPv4
applications and invokes the IPv6 socket API functions to communicate
with the IPv6 hosts, and vice versa. In order to support communication
between IPv4 applications and the target IPv6 hosts, pooled IPv4
addresses will be assigned through the name resolver in the API
translator.
This document uses terms defined in [IPv6],[TRANS-MECH] and [BIS].
2. Applicability and Disclaimer
2.1 Applicability
The main purposes of BIA are the same as BIS [BIS]. It makes IPv4
applications communicate with IPv6 hosts without any modification of
IPv4 applications. However, while BIS is for systems with no IPv6
stack, BIA is for systems with an IPv6 stack, but on which some
applications are either not yet available on IPv6 or application for
which source code is not available or lost. It's good for early
adopters who do not have all applications handy, but not for mainstream
production usage.
There is an issue about a client node running BIA trying to contact an
dual stack node on a port number that is only associated to an IPv4
application (see section 5.5). There are 2 approaches.
- The client node SHOULD cycle through all the addresses and
end up trying the IPv4 one.
- BIA SHOULD do the work.
It is not clear at this time which behavior is desirable (it may very
well be application dependent), so we need to get feedback from
experimentation.
2.2 Disclaimer
BIA SHOULD not be used for IPv4 application of which source is
available. We strongly recommend that application programers SHOULD use
this mechanism only when an application source code is not available. As
well, it SHOULD not be used for excuse not to port software or delaying
porting.
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3. Dual Stack Host Architecture using BIA
Figure 1 shows the architecture of the host in which BIA is installed.
+----------------------------------------------+
| +------------------------------------------+ |
| | | |
| | IPv4 applications | |
| | | |
| +------------------------------------------+ |
| +------------------------------------------+ |
| | Socket API (IPv4, IPv6) | |
| +------------------------------------------+ |
| +-[ API translator]------------------------+ |
| | +-----------+ +---------+ +------------+ | |
| | | Name | | Address | | Function | | |
| | | Resolver | | Mapper | | Mapper | | |
| | +-----------+ +---------+ +------------+ | |
| +------------------------------------------+ |
| +--------------------+ +-------------------+ |
| | | | | |
| | TCP(UDP)/IPv4 | | TCP(UDP)/IPv6 | |
| | | | | |
| +--------------------+ +-------------------+ |
+----------------------------------------------+
Figure 1 Architecture of the dual stack host using BIA
Dual stack hosts defined in RFC1933 [TRANS-MECH] need applications,
TCP/IP modules and addresses for both IPv4 and IPv6. The proposed hosts
in this document have an API translator to communicate with other IPv6
hosts using existing IPv4 applications. The API translator consists of 3
modules, a name resolver, an address mapper and a function mapper.
3.1 Function Mapper
It translates IPv4 socket API function into IPv6 socket API function,
and vice versa.
When detecting the IPv4 socket API functions from IPv4 applications, it
intercepts the function call and invokes new IPv6 socket API functions
which correspond to the IPv4 socket API functions. Those IPv6 API
functions are used to communicate with the target IPv6 hosts. When
detecting the IPv6 socket API functions from the data received from the
IPv6 hosts, it works symmetrically in relation to the previous case.
3.2 Name Resolver
It returns a proper answer in response to the IPv4 application's
request.
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When the IPv4 application sends a query to a name server with A records,
it detects the query, then creates another query to resolve both A and
AAAA records for the host name, and sends the query to the server.
If only the AAAA record is available, it requests the address mapper to
assign an IPv4 address corresponding to the IPv6 address, then creates
the A record for the assigned IPv4 address, and returns the A record to
the application.
NOTE: This action is the same as that of the Extension Name Resolver in
[BIS].
3.3 Address Mapper
It internally maintains a table of the pairs of an IPv4 address and an
IPv6 address. The IPv4 addresses are assigned from an IPv4 address pool.
It uses the unassigned IPv4 addresses (e.g., 0.0.0.0 ~ 0.0.0.255).
When the name resolver or the function mapper requests it to assign an
IPv4 address corresponding to an IPv6 address, it selects and returns an
IPv4 address out of the pool, and registers a new entry into the table
dynamically. The registration occurs in the following 2 cases :
(1) When the name resolver gets only an 'AAAA' record for the target
host name and there is not a mapping entry for the IPv6 address.
(2) When the function mapper gets a socket API function call from the
data received and there is not a mapping entry for the IPv6 source
address.
NOTE: This is the same as that of the Address Mapper in [BIS].
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4. Behavior Examples
This section describes behaviors of the proposed dual stack host called
"dual stack", which communicates with an IPv6 host called "host6" using
an IPv4 application.
In this section, the meanings of arrows are as follows :
---> A DNS message for name resolving created by the
applications and the name resolver in the API translator.
+++> An IPv4 address request to and reply from the address mapper
for the name resolver and the function mapper.
===> Data flow by socket API functions created by the
applications and the function mapper in the API translator.
4.1 Originator Behavior
This sub-section describes the behavior when the "dual stack" sends data
to "host6".
When an IPv4 application sends a DNS query to its name server, the name
resolver intercepts the query and then creates a new query to resolve
both A and AAAA records. When only the AAAA record is resolved, the name
resolver requests the address mapper to assign an IPv4 address
corresponding to the IPv6 address.
The name resolver creates an A record for the assigned IPv4 address and
returns it to the IPv4 applications.
In order for the IPv4 application to send IPv4 packets to host6, it
calls the IPv4 socket API function.
The function mapper detects the socket API function from the
application. If the result is from IPv6 applications, it skips the
translation. In the case of IPv4 applications, it requires an IPv6
address to invoke the IPv6 socket API function, thus the function mapper
requests an IPv6 address to the address mapper. The address mapper
selects an IPv4 address from the table and returns the destination IPv6
address. Using this IPv6 address, the function mapper invokes an IPv6
socket API function corresponding to the IPv4 socket API function.
When the function mapper receives an IPv6 function call,it requests the
IPv4 address to the address mapper in order to translate the IPv6 socket
API function into an IPv4 socket API function. Then, the function mapper
invokes the socket API function for the IPv4 applications.
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Figure 2 illustrates the behavior described above:
"dual stack" "host6"
IPv4 Socket | [ API Translator ] | TCP(UDP)/IP Name
appli- API |Name Address Function| (v6/v4) Server
cation |Resolver Mapper Mapper |
| | | | | | | |
<<Resolve an IPv4 address for "host6".>> | | |
| | | | | | | |
|--------|------->| Query of 'A' records for host6. | |
| | | | | | | |
| | |--------|--------|---------|--------------|------>|
| | | Query of 'A' records and 'AAAA' for host6 |
| | | | | | | |
| | |<-------|--------|---------|--------------|-------|
| | | Reply only with 'AAAA' record. | |
| | | | | | |
| | |<<Only 'AAAA' record is resolved.>> |
| | | | | | |
| | |+++++++>| Request one IPv4 address |
| | | | corresponding to the IPv6 address.
| | | | | | |
| | | |<<Assign one IPv4 address.>> |
| | | | | | |
| | |<+++++++| Reply with the IPv4 address. |
| | | | | | |
| | |<<Create 'A' record for the IPv4 address.>>
| | | | | | |
|<-------|--------| Reply with the 'A' record.| |
| | | | | | |
Figure 2 Behavior of the originator (1/2)
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"dual stack" "host6"
IPv4 Socket | [ API Translator ] | TCP(UDP)/IP
appli- API |Name Address Function| (v6/v4)
cation |Resolver Mapper Mapper |
| | | | | | |
<<Call IPv4 Socket API function >> | | |
| | | | | | |
|========|========|========|=======>|An IPv4 Socket API function Call
| | | | | | |
| | | |<+++++++| Request IPv6 addresses|
| | | | | corresponding to the |
| | | | | IPv4 addresses. |
| | | | | | |
| | | |+++++++>| Reply with the IPv6 addresses.
| | | | | | |
| | | | |<<Translate IPv4 into IPv6.>>
| | | | | | |
| An IPv6 Socket API function call.|=========|=============>|
| | | | | | |
| | | | |<<Reply an IPv6 data |
| | | | | to dual stack.>> |
| | | | | | |
| An IPv6 Socket API function call.|<========|==============|
| | | | | | |
| | | | |<<Translate IPv6 into IPv4.>>
| | | | | | |
| | | |<+++++++| Request IPv4 addresses|
| | | | | corresponding to the |
| | | | | IPv6 addresses. |
| | | | | | |
| | | |+++++++>| Reply with the IPv4 addresses.
| | | | | | |
|<=======|========|========|========| An IPv4 Socket function call.
| | | | | | |
Figure 2 Behavior of the originator (2/2)
4.2 Recipient Behavior
This subsection describes the recipient behavior of "dual stack". The
communication is triggered by "host6".
"host6" resolves the address of "dual stack" with 'AAAA' records through
its name server, and then sends an IPv6 packet to the "dual stack".
The IPv6 packet reaches the "dual stack" and the function mapper detects
it.
The function mapper requests the IPv4 address to the address mapper in
order to invoke the IPv4 socket API function to communicate with for
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IPv4 application. Then the function mapper invokes the corresponding
IPv4 socket API function for the IPv4 applications corresponding to the
IPv6 functions.
Figure 3 illustrates the behavior described above:
"dual stack" "host6"
IPv4 Socket | [ API Translator ] | TCP(UDP)/IP
appli- API |Name Address Function| (v6/v4)
cation |Resolver Mapper Mapper |
| | | | | | |
<<Receive data from "host6".>> | | |
| | | | | | |
| An IPv6 Socket function call.|<========|==============|
| | | | | | |
| | | |<+++++++| Request IPv4 addresses|
| | | | | corresponding to the IPv6
| | | | | addresses. |
| | | | | | |
| | | |+++++++>| Reply with the IPv4 addresses.
| | | | | | |
| | | | |<<Translate IPv6 into IPv4.>>
| | | | | | |
|<=======|========|========|========| An IPv4 function call |
| | | | | | |
<<Reply an IPv4 data to "host6".>> | | |
| | | | | | |
|========|========|========|=======>| An IPv4 function call |
| | | | | | |
| | | | |<<Translate IPv4 into IPv6.>>
| | | | | | |
| | | |<+++++++| Request IPv6 addresses|
| | | | | corresponding to the IPv4
| | | | | addresses. |
| | | | | | |
| | | |+++++++>| Reply with the IPv6 addresses.
| | | | | | |
| An IPv6 Socket function call.|=========|=============>|
| | | | | | |
Figure 3 Behavior of Receiving data from IPv6 host
5. Considerations
5.1 Socket API Conversion
IPv4 socket API functions are translated into semantically the same IPv6
socket API functions and vice versa. See Appendix A for the API list
intercepted by BIA. IP addresses embedded in application layer
protocols (e.g., FTP) can be translated in API functions. Its
implementation depends on operating systems.
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NOTE: Basically, IPv4 socket API functions are not fully compatible with
IPv6 since the IPv6 has new advanced features.
5.2 ICMP Message Handling
When an application needs ICMP messages values (e.g., Type, Code, etc.)
sent from a network layer, ICMPv4 message values SHOULD be translated
into ICMPv6 message values based on [SIIT], and vice versa. It can be
implemented using raw socket.
5.3 IPv4 Address Pool and Mapping Table
The address pool consists of the unassigned IPv4 addresses. However, if
a number of IPv4 applications communicate with IPv6 hosts, the available
address spaces will be exhausted. As a result, it will be impossible for
IPv4 applications to communicate with IPv6 hosts. It requires smart
management techniques for address pool. For example, it is desirable
for the mapper to free the oldest entry and re-use the IPv4 address for
creating a new entry. This issues is the same as [BIS].
5.4 Internally Assigned IPv4 Addresses
The IPv4 addresses, which are internally assigned to IPv6 target hosts
out of the pool, are the unassigned IPv4 addresses (e.g., 0.0.0.0 ~
0.0.0.255). There is no potential collision with another use of the
private address space when the IPv4 address flows out from the host.
5.5 Mis-match between DNS result(AAAA) and Peer Application version(v4)
If a server application you are using does not support IPv6 yet, but
runs on an machine that supports other IPv6 services and this is listed
with a AAAA record in the DNS, a client IPv4 application using BIA will
fail to connect to the server application, because there is a mis-match
between DNS query result (i.e., AAAA) and a server application
version(i.e., IPv4). A solution is to try all the addresses listed in
the DNS and just not fail after the first attempt. We have two
approaches : the client application itself SHOULD cycle through all the
addresses and end up trying the IPv4 one. Or it SHOULD be done by some
extensions of name resolver and API translator in BIA. For this, BIA
SHOULD do iterated jobs for finding the working address used by the
other application out of addresses returned by the extended name
resolver. It may very well be application dependent.
5.6 Implementation Issues
Some operating systems support the pre-load library functions, so it is
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easy to implement the API translator by using it. For example, user can
replace all existing socket API functions with user-defined socket API
functions which translate the socket API function. In this case, every
IPv4 application has its own translation library using pre-load library
which will be bound into the application before executing it
dynamically.
The other operating systems support the user-defined layered protocol
allowing a user to develop some additional protocols and put them in the
existing protocol stack. In this case, the API translator can be
implemented as a layered protocol module.
In the above two approaches, it is assumed that there exists both
TCP(UDP)/IPv4 and TCP(UDP)/IPv6 stacks and there is no need to modify or
to add a new TCP-UDP/IPv6 stack.
6. Limitations
In common with [NAT-PT], BIA needs to translate IP addresses embedded in
application layer protocols, e.g., FTP. So it may not work for new
applications which embed addresses in payloads.
This mechanism supports unicast communications only. If it can support
multicast functions, some other additional functionalities must be
considered in the function mapper module.
Since the IPv6 API has new advanced features, it is difficult to
translate such kind of IPv6 APIs into IPv4 APIs. Thus, IPv6 inbound
communication with advanced features may be discarded.
7. Security Considerations
The security consideration of BIA mostly relies on that of [NAT-PT].
The differences are due to the address translation occuring at the API
and not in the network layer. That is, since the mechanism use the API
translator at the socket API level, hosts can utilize the security of
network layer (e.g., IPsec) when they communicate with IPv6 hosts using
IPv4 applications via the mechanism. As well, there isn't a DNS ALG as
in NAT-PT, so there is no interference with DNSSEC.
The use of address pooling may open a denial of service attack
vulnerability. However, this security hazard may be prohibited, since
the pooled IPv4 addresses will not be used for the outside IPv4 routing
(these addresses are assigned from the unassigned IPv4 addresses (e.g.,
0.0.0.0 ~ 0.0.0.255) by the address mapper).
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8. Acknowledgments
We would like to acknowledge the implementation contributions by Wanjik
Lee(wjlee@arang.miryang.ac.kr) and i2soft Corporation(www.i2soft.net).
9. References
[TRANS-MECH] Gilligan, R. and E. Nordmark, "Transition Mechanisms for
IPv6 Hosts and Routers", RFC 2893, August 2000.
[SIIT] Nordmark, E., "Stateless IP/ICMP Translator (SIIT)", RFC
2765, February 2000.
[FTP] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[NAT] Kjeld B. and P. Francis, "The IP Network Address
Translator (NAT)", RFC 1631, May 1994.
[IPV4] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[PRIVATE] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J. and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, February 1996.
[NAT-PT] Tsirtsis, G. and P. Srisuresh, "Network Address
Translation - Protocol Translation (NAT-PT)", RFC 2766,
February 2000.
[BIS] K. Tsuchiya, H. Higuchi, Y. Atarashi, "Dual Stack Hosts
using the "Bump-In-the-Stack" Technique (BIS)", RFC 2767,
February 2000.
[SOCK-EXT] R. Gilligan, S. Thomson, J. Bound and W. Stevens, "Basic
Socket Interface Extensions for IPv6", RFC2553, March 1999.
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Appendix A : API list intercepted by BIA
The following functions are the API list which SHOULD be intercepted by
BIA module.
The functions that the application uses to pass addresses into the
system are:
bind()
connect()
sendmsg()
sendto()
The functions that return an address from the system to an application
are:
accept()
recvfrom()
recvmsg()
getpeername()
getsockname()
The functions that are related to socket options are :
getsocketopt()
setsocketopt()
The functions that are used for conversion of IP addresses embedded in
application layer protocol (e.g., FTP, DNS, etc.) are:
recv()
send()
As well, raw sockets for IPv4 and IPv6 SHOULD be intercepted.
Most of the socket functions require a pointer to the socket address
structure as an argument. Each IPv4 argument is mapped into
corresponding an IPv6 argument, and vice versa.
According to [SOCK-EXT], the following new IPv6 basic APIs and
structures are required.
IPv4 new IPv6
------------------------------------------------
AF_INET AF_INET6
sockaddr_in sockaddr_in6
gethostbyname() getaddrinfo()
gethostbyaddr() getnameinfo()
inet_ntoa()/inet_addr() inet_pton()/inet_ntop()
INADDR_ANY in6addr_any
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Authors Addresses
Seungyun Lee
ETRI PEC
161 Kajong-Dong, Yusong-Gu, Taejon 305-350, Korea
Tel : +82 42 860 5508
Fax : +82 42 861 5404
Email : syl@pec.etri.re.kr
Myung-Ki Shin
ETRI PEC
161 Kajong-Dong, Yusong-Gu, Taejon 305-350, Korea
Tel : +82 42 860 4847
Fax : +82 42 861 5404
Email : mkshin@pec.etri.re.kr
Yong-Jin Kim
ETRI PEC
161 Kajong-Dong, Yusong-Gu, Taejon 305-350, Korea
Tel : +82 42 860 6564
Fax : +82 42 861 5404
Email : yjkim@pec.etri.re.kr
Alain Durand
Sun Microsystems
901 San Antonio Road
UMPK 17-202
Palo Alto, CA 94303-4900, USA
Tel : +1 650 786 7503
Fax : +1 650 786 5896
Email : Alain.Durand@sun.com
Erik Nordmark
Sun Microsystems, Inc.
901 San Antonio Road
Palo Alto, CA 94303, USA
Tel : +1 650 786 5166
Fax : +1 650 786 5896
Email : nordmark@sun.com
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