One document matched: draft-ietf-ngtrans-socks-gateway-04.txt
Differences from draft-ietf-ngtrans-socks-gateway-03.txt
INTERNET-DRAFT H. Kitamura
<draft-ietf-ngtrans-socks-gateway-04.txt> NEC Corporation
Expires in six months 6 April 2000
A SOCKS-based IPv6/IPv4 Gateway Mechanism
<draft-ietf-ngtrans-socks-gateway-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 Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
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
http://www.ietf.org/shadow.html.
Abstract
This document describes an IPv6/IPv4 gateway mechanism that is based
on the SOCKS protocol [SOCKSv5]. By applying the SOCKS mechanism to
support the heterogeneous communications relays between IPv6 and IPv4
at the SOCKS server, the SOCKS-based IPv6/IPv4 gateway mechanism is
accomplished.
Since it is accomplished without introducing new protocols, it
provides the same communication environment that is provided by the
SOCKS mechanism. The same appearance is provided to the heterogeneous
communications. No conveniences or functionalities of current
communications are sacrificed.
The SOCKS-based gateway mechanism enables smooth heterogeneous
communications between the IPv6 nodes and IPv4 nodes.
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1. Introduction
This document describes an IPv6/IPv4 gateway mechanism that is based
on the SOCKS protocol [SOCKSv5]. By applying the SOCKS mechanism to
support heterogeneous communications, the SOCKS-based IPv6/IPv4
gateway mechanism is accomplished.
The SOCKS-based gateway mechanism is designed to satisfy the
following requirements.
1. Maintain the conveniences of current IPv4 communication methods
and frameworks (infrastructure) of existing communication networks
(e.g., DNS).
2. Utilize existing user applications that are designed only for IPv4
communications to heterogeneous communications without modifying
them.
3. Be scalable and able to support the translations for various IPv4
and IPv6 communication services.
4. Can easily introduce IPv6 new features (e.g., IPSec).
Since the SOCKS-based IPv6/IPv4 gateway mechanism is based on a
mechanism that relays two "terminated" IPv4 and IPv6 connections at
the "application layer", its characteristics are inherited from those
of the connection relay mechanism at the application layer and those
of the native SOCKS mechanism.
The SOCKS-based IPv6/IPv4 gateway mechanism does not require any
modifications to the DNS system, because it has a feature that
enables the DNS name resolving actions of SOCKS clients to be
delegated to an enhanced SOCKS server that has both IPv6 and IPv4
stacks.
This DNS name resolving delegation is enabled by socksifying
applications. Socksifying is a constraint of the mechanism. However,
it is necessary to socksify applications to eliminate the need to
modify the DNS system. Thus, there is a dilemma in that either
socksification or DNS modification is necessary.
Since the SOCKS is originally designed for firewall security systems,
it supports various connections relay topologies and provides
sufficient authentication methods for the connection relays. Since
the SOCKS-based gateway mechanism inherits the characteristics, it
has much flexibility in supporting various relay topologies that mix
IPv4 and IPv6 communications, and the relayed connections can be
authenticated by the native SOCKS authentication methods.
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2. Basic SOCKS-based Gateway Mechanism
Figure 1 shows the basic SOCKS-based gateway mechanism.
Client C Gateway G Destination D
+-----------+ (Server)
|Application|
+-->+===========+ +-------------+ +-----------+
same-+ |*SOCKS Lib*| | *Gateway* | |Application|
API +-->+===========+ +=====---=====+ +-----------+
| Socket DNS| | Socket DNS | | Socket DNS|
+-----------+ +-------------+ +-----------+
| [ IPv X ] | |[IPvX]|(IPvY)| | ( IPv Y ) |
+-----------+ +-------------+ +-----------+
|Network I/F| | Network I/F | |Network I/F|
+-----+-----+ +---+-----+---+ +-----+-----+
| | | |
+============+ +------------+
socksified normal
connection connection
(ctrl)+data data only
Fig. 1 Basic SOCKS-based Gateway Mechanism
In this figure, the Client C initiates the communication to the
Destination D. Two new functional blocks that compose the system are
introduced.
One, *Socks Lib*, is introduced into the client side (Client C) (this
procedure is called "socksifying"). It is located between application
layer and socket layer, and can replace applications' socket APIs and
DNS name resolving APIs (e.g., gethostbyname(), getaddrinfo() etc.)
dynamically. A delegation mapping table exists in it for a "DNS name
resolving delegation" feature (described below). Each socksified
application has its own *Socks Lib*.
The other, *Gateway*, is an enhanced SOCKS server. It is installed on
the IPv6 and IPv4 dual stack node (Gateway G). All types of protocol
combinations are relayed there between Client C (IPvX) and
Destination D (IPvY). The *Socks Lib* invokes it. Each *Gateway*
takes charge of one socksified connection.
The following four types of combinations of IPvX and IPvY are
possible in this mechanism.
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type C ------ G ------ D
[IPvX] (IPvY)
A IPv4 IPv4 homogeneous (normal SOCKS)
B IPv4 IPv6 * heterogeneous *
C IPv6 IPv4 * heterogeneous *
D IPv6 IPv6 homogeneous
Type A is supported by the normal SOCKS mechanism. Type B and C are
the main targets for the SOCKS-based gateway mechanism. They provide
heterogeneous communication topologies. Type D can be supported by
the natural extension of the SOCKS mechanism, because it is a
homogeneous communication.
The *Socks Lib* communicates with the *Gateway* by using SOCKS
protocol [SOCKSv5]. The connection between the Client C and the
Gateway G is called a "socksified connection." It can transfer not
only data but also control information (e.g. location information of
the Destination, etc.).
In order to provide appropriate destination information to the
application on the Client C, the *Socks Lib* also replaces other
types of socket APIs (e.g., getpeername(), etc.) that provide
information about the destination, and necessary information for this
replacement is transferred via the socksified connection. This
mechanism provides the same usability of current communication
methods to the applications on the Client C, and it is not necessary
to modify the applications at all to utilize this mechanism.
The connection between the Gateway G and the Destination D is an
ordinary connection. Server applications on Destination D understand
that the source of the connection is the Gateway G (not Client C). It
is not necessary to modify (socksify) them.
Since no new special SOCKS protocols are introduced in the mechanism,
there is no difference in appearance among these four combinations.
The address family information of the Destination D mainly decides a
communication type from these combinations.
3. DNS Name Resolving Procedure
As [TRANSMECH] mentioned, it is essential for the transition
mechanisms to cooperate with the DNS name resolving mechanism. The
SOCKS-based gateway mechanism has the capability to cooperate with it
without modifying the DNS system.
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In this section, the procedure of how the SOCKS-based gateway
mechanism cooperates with the DNS name resolving mechanism is
described.
In the SOCKS protocol specification [SOCKSv5], it is defined that
IPv4 address, IPv6 address, and DOMAINNAME (FQDN) information can be
used in the ATYP (address type) field of the SOCKS protocol format.
Since DOMAINNAME (FQDN) information can be used in the ATYP (address
type) field, it becomes possible to delegate the DNS name resolving
action at the SOCKS clients to the DNS name resolving action at the
SOCKS server. This feature is called "DNS name resolving delegation".
Effective use of "DNS name resolving delegation" enables smooth
heterogeneous communications between the IPv6 nodes and IPv4 nodes
without modifying applications.
Typical "socksification" is accomplished by dynamically changing the
linking order of dynamic link libraries (specifically, by linking the
SOCKS dynamic link library before the dynamic link libraries for
normal socket and DNS name resolving APIs). So, it is not necessary
to modify applications (change their source codes and recompile them,
etc.) in typical "socksification".
In order to accomplish the "DNS name resolving delegation", a
delegation mapping table is prepared in *Socks Lib* (at the client).
This is an internal table between a socksified application and its
*Socks Lib*. It is local and independent of other applications or
their *Socks Lib*s. In the delegation mapping table, a "fake IP"
address is used as a key to look up the corresponding FQDN
information, and it is information that is replied to the
application.
The transparentness to applications is maintained in the "DNS name
resolving delegation", because it is accomplished by dynamically
replacing DNS name resolving APIs with the *Socks Lib*. It is not
necessary to modify applications on the client. By calling a DNS name
resolving API, a "DNS name resolving delegation" is internally
executed. Socksified applications can run as usual, and there is no
need to be concerned about the existence of the "DNS name resolving
delegation".
The "DNS name resolving delegation" is accomplished only when FQDN
information is used in the ATYP (address type) field of the SOCKS
command. Therefore, it is mandatory to do so for the heterogeneous
communications between the IPv6 nodes and IPv4 nodes.
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The method of using FQDN information in the ATYP field depends on the
configuration setting and implementation of the SOCKS protocol. In
order to simplify the discussion, only the case in which the FQDN
information is used in the ATYP field is discussed here.
The detailed internal procedure of the "DNS name resolving
delegation" is as follows.
1. An application on the source terminal (Client C) tries to get the
IP address information of the destination terminal (Destination D)
by calling the DNS name resolving function (e.g.,
gethostbyname()). At this time, the logical host name ("FQDN")
information of the Destination D is passed to the application's
*Socks Lib* as an argument of called APIs.
2. Since the *Socks Lib* has replaced such DNS name resolving APIs,
the real DNS name resolving APIs is not called here. The argued
"FQDN" information is merely registered into a delegation mapping
table in *Socks Lib*, and a "fake IP" address is selected as
information that is replied to the application from a reserved
special IP address space that is never used in real communications
(e.g., 0.0.0.x). The address family type of the "fake IP" address
must be suitable for requests called by the applications. Namely,
it must belong to the same address family of the Client C, even if
the address family of the Destination D is different from it.
After the selected "fake IP" address is registered into the
delegation mapping table as a pair with the "FQDN", it is replied
to the application.
3. The application receives the "fake IP" address, and prepares a
"socket". The "fake IP" address information is used as an element
of the "socket". The application calls socket APIs (e.g.,
connect()) to start a communication. The "socket" is used as an
argument of them.
4. Since the *Socks Lib* has replaced such socket APIs, the real
socket function is not called. The IP address information of the
argued socket is checked. If the address belongs to the special
address space for the fake address, the matched registered "FQDN"
information of the "fake IP" address is obtained from the
delegation mapping table.
5. The "FQDN" information is transferred to the *Gateway* on the
relay server (Gateway G) by using the SOCKS command that is
matched to the called socket APIs. (e.g., in case of connect(),
the CONNECT command is used.)
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6. Finally, the real DNS name resolving API (e.g., getaddrinfo()) is
called at the *Gateway*. At this time, the received "FQDN"
information via the SOCKS protocol is used as an argument of the
called APIs.
7. The *Gateway* obtains the "real IP" address from a DNS server,
and creates a "socket". The "real IP" address information is used
as an element of the "socket".
8. The *Gateway* calls socket APIs (e.g., connect()) to communicate
with the Destination D. The "socket" is used as an argument of
them.
By using this mechanism, DNS name resolving actions are delegated
from the source terminal (Client C) to the relay server (Gateway G).
(Restrictions on applicability of "fake IP" address, etc. are
described in Section 6.)
* DNS Name Resolving Delegation and Address Mapping
In the "DNS name resolving delegation", the real DNS name resolving
actions are taken at the relay server (Gateway G). Since the relay
server is an IPv4 and IPv6 dual stack node, DNS name resolving
queries for any address family types of destinations can be done
without causing problems. Therefore, it is not necessary to modify
the existing DNS mechanism at all.
Without this feature, an IPv4 application can not resolve the host
name of an IPv6 destination. Even if it can get the IPv6 address by
some method, it is impossible for the IPv4 application to deal with
such an IPv6 address. It is impossible because the IPv6 address is
four times longer than the IPv4 address, and the IPv4 application
does not have any long address space in which to store it.
Using this feature brings forth an additional feature: an IPv4
application can also use a numerical IPv6 address expression to
specify an IPv6 destination terminal. Since the IPv6 address
expression includes colons (":"), it is identified as an FQDN
expression (not a numerical IP expression) for the IPv4 application.
Thus the numerical IPv6 address expression is treated the same as the
DNS expression in the "DNS name resolving delegation" feature.
The problem with the feature is that a failure of the DNS name
resolving process is detected incorrectly at the source terminal
(Client C). It is detected as a failure of the connection creation.
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* Address Mapping-like Operations
The SOCKS-based gateway mechanism has the ability to manage address
translation and mapping wisely. It does not require the reserving of
a wide global address space for the address mapping, and complex
address allocation and management mechanisms are not necessary,
because address mapping-like operations are done at the *Socks Lib*
by using the fake IP address and the delegation mapping table. Since
the delegation mapping table is prepared for each application, it is
locally closed and independent of other applications. Therefore, it
is easy to manage the table, and it is not necessary to reserve a
wide global address space.
4. Multiple Chained Relay Mechanism (Advanced usage)
The SOCKS-based gateway mechanism has the flexibility to support
multiple chained relay topologies. With the mechanism, IPv4 and IPv6
mixed various communication topologies are accomplished.
Figure 2 shows the structure of the multiple chained relay mechanism.
Client C Gateway G1 Gateway G2 Destination D
+-----------+ (Server 1) (Server 2)
|Application|
+===========+ +-------------+ +-------------+ +-----------+
|*SOCKS Lib*| | *Gateway1* | | *Gateway2* | |Application|
+===========+ +=====---=====+ +=====---=====+ +-----------+
| Socket DNS| | Socket DNS | | Socket DNS | | Socket DNS|
+-----------+ +-------------+ +-------------+ +-----------+
| [ IPv X ] | |[IPvX]|(IPvY)| |(IPvY)|{IPvZ}| | { IPv Z } |
+-----------+ +-------------+ +-------------+ +-----------+
|Network I/F| | Network I/F | | Network I/F | |Network I/F|
+-----+-----+ +---+-----+---+ +---+-----+---+ +-----+-----+
| | | | | |
+============+ +==========+ +------------+
socksified socksified normal
connection connection connection
(ctrl)+data (ctrl)+data data only
Fig. 2 Multiple Chained Relay Mechanism
In this figure, the source terminal (Client C) initiates the
communication with the destination (Destination D). Underneath, the
connection is replaced with three connections, and they are relayed
at the two relay servers (Gateway G1 and G2). The *Gateway* includes
the same type of functions of *Socks Lib*. By enabling the *Socks
Lib* functions at the *Gateway1* on the first relay server (Gateway
G1), the multiple chained relay topology is accomplished.
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There is no limitation on the number of relay operations between the
source terminal and the destination terminal. It is possible to have
more than two intermediate relay servers. To simplify the
explanation, a twice-relayed topology is shown here. All types of the
protocol relay combinations are possible.
In case of twice-relayed topology, the following eight types of
combinations of IPvX, IPvY, and IPvZ are possible.
type C ------ G1 ------ G2 ------ D
[IPvX] (IPvY) {IPvZ}
E IPv4 IPv4 IPv4 homogeneous (normal SOCKS)
F IPv4 IPv4 IPv6 * heterogeneous *
G IPv4 IPv6 IPv4 * heterogeneous * (tunnel-like)
H IPv4 IPv6 IPv6 * heterogeneous *
I IPv6 IPv4 IPv4 * heterogeneous *
J IPv6 IPv4 IPv6 * heterogeneous * (tunnel-like)
K IPv6 IPv6 IPv4 * heterogeneous *
L IPv6 IPv6 IPv6 homogeneous
Type E is supported by the normal SOCKS mechanism. The types from F
to K are the main targets for the gateway mechanisms. They provide
heterogeneous communication topologies. Type L can be supported by
the natural extension of the SOCKS mechanism, because it is a
homogeneous communication.
Type G and type J can provide interesting topology cases. They are
similar to the topologies that the tunneling techniques can provide.
However, their characteristics are different.
* Packet Size Adjustment
Since the length of the IPv6 header is different from the length of
the IPv4 header, it is necessary to consider the packet size
adjustment in heterogeneous communications. If this is not taken
into consideration, the packet size may exceed the MTU of the
network. Since the SOCKS-based IPv6/IPv4 gateway mechanism is
based on an "application layer" connection relay mechanism, the
packet size is naturally adjusted at the application layer and it
never exceeds the MTU of the network.
* Authenticated Relay
Since the SOCKS is originally designed for firewall systems and it
has various authentication methods, the relayed connections can be
authenticated by the native SOCKS authentication methods.
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5. Characteristics of the SOCKS-based gateway mechanism
In this section, the characteristics of the SOCKS-based gateway
mechanism are summarized.
1. DNS modification is not necessary:
It is not necessary to reserve a wide global address space for
address mapping.
Also, address map servers are not necessary, because there is a
"DNS Name Resolving Delegation" mechanism.
2. Application independent:
If the applications use socket APIs and DNS name resolving APIs,
the gateway mechanism is applied to them, since the mechanism is
accomplished by replacing these APIs that at the *Socks Lib*.
As most communication programs use these APIs, there is no
application dependency.
(Applications that exchange IP address information with peers are
exceptions)
3. Independent of OS and NIC types:
Since the *Socks Lib* and the *Gateway* run at the application
layer, the SOCKS-base gateway mechanism runs on any of the
platforms of either UNIX or Windows OSs, and there is no
dependency on the type of physical NIC.
4. Only an easy socksification procedure is necessary:
It is easy to install the *Socks Lib* (socksify) to the source
terminal, because the dynamic link library technique helps this
procedure.
5. IPv6 new features (e.g., IPSec) can be utilized easily:
Since connections are first terminated and then relayed at the
*Gateway*, it is easy to enable IPv6 new features on the IPv6
side.
6. Current existing client SOCKSv5 library can be used:
For the IPv4 -> IPv6 relay, the current existing client SOCKSv5
library that is designed for IPv4 -> IPv4 communication can be
used without modification.
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7. Both TCP and UDP relays are possible:
Since the SOCKS protocol supports both TCP and UDP relays, this
mechanism can also relay both TCP and UDP connections.
8. Both IPv4 -> IPv6 and IPv6 -> IPv4 relays are possible:
This mechanism can accomplish not only the IPv4 -> IPv6 relay but
also the IPv6 -> IPv4 relay with the same method.
9. Multiple chained relays are possible:
Since the mechanism has flexibility, all types of protocol
combinations of multiple chained relays are possible.
10. Exceptional applications are supported that exchange IP address
information at the application level:
It is easy for the SOCKS-based gateway mechanism to introduce
special management routines. If such protocols as ftp are known,
the SOCKS-based gateway mechanism can support them by introducing
special protocol translation routines.
(Implementations of the SOCKS-based gateway mechanism have
supported the ftp protocol translation [see Appendix A])
11. Easy load balancing:
Since the *Gateway* is installed as a server, it is easy to
balance the load by supplying multiple servers.
6. Applicability statement
The SOCKS-based gateway mechanism requests socksification of
applications (install *Socks Lib*) to accomplish heterogeneous
communications. Since typical socksification is done by changing the
linking order of dynamic link libraries, it is not difficult.
However, it is one of the constraints for users.
In order to eliminate the need to modify the DNS system, the
socksification is necessary in the mechanism. Thus, there is a
dilemma in that either socksification or DNS modification is
necessary.
Other than the socksification, the SOCKS-based gateway mechanism has
the following three types of constraints.
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1. Essential constraints:
Constraints are caused by the address length difference between
IPv4 and IPv6.
Functions that request an IP address as one of the return values
(e.g., getpeername() and getsockname() etc.) can not provide the
correct IP address as a return value. However, an appropriate
port value can be provided, because IPv4 and IPv6 use the same
size port space and necessary port information is transferred by
the SOCKS protocol.
From a realistic viewpoint, this is a minor constraint, because
such functions are mainly called in order to get port information
(not IP address information).
2. Constraints of the SOCKS mechanism:
Since the current SOCKS system can not socksify all of the tricky
applications in which extraordinary manners are used to create
connections, the SOCKS-based gateway mechanism can not be applied
to them.
3. Constraints to deal with the fake address:
The fake address must be dealt with as a temporary value at the
application; it must not be recorded permanently as a bookmark,
etc. After the application is finished, the fake address
information must be released. Otherwise, problems will occur.
From a realistic viewpoint, this is also a minor constraint,
because most applications record FQDN information instead of
(fake) IP addresses.
7. Security Considerations
Since the SOCKS-based IPv6/IPv4 gateway mechanism is based on
SOCKSv5 protocol, the security feature of the mechanism matches
that of SOCKSv5. It is described in the Security Considerations
section of the SOCKS Protocol Version 5 [SOCKSv5].
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Appendix A. Implementations
Currently, there are two independent implementations of the SOCKS-
based IPv6/IPv4 gateway mechanism. Both of them are open to the
public.
One is NEC's implementation. Its source codes are available at the
following URL.
http://www.socks.nec.com/
The other is Fujitsu Lab.'s implementation, which is called
"SOCKS64." Its source codes are available at the following URL.
ftp://ftp.kame.net/pub/kame/misc/socks64-...
Appendix B. Experiments
We have been testing SOCKS64, one of the SOCKS-based gateway
implementations in many environments. Since July 1998, we have been
running the SOCKS64 server in between the 6bone and the internal
network of Fujitsu Ltd., Japan. Computers in Fujitsu's internal
network already have been "socksified", so users can connect to 6bone
hosts merely by selecting our SOCKS64 server as their SOCKS gateway.
For an interoperability test, we have been providing a SOCKS64 server
in the WIDE Project[WIDEV6WG] Camp, where about 200 Internet
researchers are participating. A temporary network called "camp-net"
is constructed at the camp for a variety of experiments and provides
services to the attendees. More than a hundred hosts are connected to
the camp-net.
In these environments, we have tested many types of SOCKS5 clients,
including the SocksCap32[SOCKSCAP] on Windows and a variety of UNIX
based SOCKS libraries, and confirmed any clients successfully
connected to the IPv6 hosts using telnet, ftp, http, ssh.
Also we have tested a very complicated interconnection of IPv4 and
IPv6. At the WIDE camp held in September 1998, we constructed an
IPv4 over IPv6 tunnel using the SOCKS64 and the FAITH translator. In
this system, the SOCKS5 clients had no problems connecting to the
IPv4 hosts through the IPv6 networks.
IPv4 host --SOCKS-- SOCKS64 --IPv6-- IPv6-IPv4 -- IPv4 host
/IPv4 server translator
In conclusion, SOCKS64 provides an easy and sure way to let IPv4
hosts connect to IPv6 hosts.
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References
[SOCKSv5] Leech, M., Ganis, M., Lee, Y., Kuris, R. Koblas, D., &
Jones, L., "SOCKS Protocol V5," RFC1928, April 1996.
[TRANSMECH] R. Gilligan and E. Nordmark, "Transition Mechanisms for
IPv6 Hosts and Routers", RFC 1933, April 1996.
[IPv6] S. Deering, R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification," RFC2460, December 1998.
[INET99] H. Kitamura, "Entering the IPv6 communication world by
the SOCKS-based IPv6/IPv4 Translator,"
in Proceedings of INET99, July 1999.
[WIDEV6WG] WIDE Project IPv6 Working Group, "WIDE Project IPv6
Working Group Home Page", http://www.v6.wide.ad.jp/.
[SOCKSCAP] NEC, "SocksCap Web Page",
http://www.socks.nec.com/sockscap.html.
Authors' Addresses:
Hiroshi Kitamura
NEC Corporation
NEC NETWORKS, Networks Development Labratories
(Igarashi Building) 11-5, Shibaura 2-Chome,
Minato-Ku, Tokyo 108-8557, JAPAN
Phone: +81 (3) 5476-1071
Fax: +81 (3) 5476-1005
Email: kitamura@da.jp.nec.com
H. Kitamura [Page 14]
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