[public-tsp] / pubtsp.man

.TH PUBTSP 8 "December 12, 2010"
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.SH NAME
pubtsp \- server-side daemon for public TSP service
.SH SYNOPSYS
.B pubtsp
[\fB\-t\fR \fI/dev/tunX\fR] \fB\-l\fR \fIv4addr\fR \fB\-L\fR \fIv6prefix/64\fR
.B pubtsp
\fB\-h\fR
.SH DESCRIPTION
.PP
Through a \fBpubTSP\fR daemon, it is possible to make an IPv6 range of
addresses available to IPv4-only users.  This means that even an IPv4-only
network can host IPv6-only applications, as long as they can fall back on
a tunnel based on this profile.
.PP
TSP, or the Tunnel Setup Protocol, is documented in RFC 5722.  It defines
several methods for encapsulating IPv6 traffic in IPv4 packets.  It also
defines SASL as its generic authentication layer.
.PP
This daemon implements a specific profile for the server side of TSP.
The profile of RFC 5722 implemented by this daemon supports NAT traversal
for public use.  The purpose of this profile is to provide a fallback
mode to IPv6-only devices running on an IPv4-only network; the idea is
to make such a fallback possible without needing to configure a tunnel.
.PP
The NAT traversing aspect of this profile is needed to support the normal
openness of IPv6 connections.  This is achieved by packing IPv6 into UDP
and then into IPv4.  This is a guaranteed manner of traversing NAT,
provided that this daemon listens to a public IPv4 address.  The daemon
currently does not support any other modes of operation.
.PP
The public-use aspect of this profile means that there is no requirement for
clients to register.  In terms of SASL, this uses the ANONYMOUS method of
authentication.  However, this does not mean that the use of \fBpubTSP\fR
makes it possible to browse IPv6 networks anonymously; in order to
ensure traceability of abusive behaviour, the IPv4 address and UDP port
of the tunnel client are mentioned in the IPv6 address.  See ADDRESS FORMAT
below for details, and SECURITY CHECKS for further precautions against abuse.
.PP
The foreseen application of servers under this profile of TSP are
IPv6-only services that are accessed from an IPv4-only network.  The pivotal
point of defining IPv6-only service can be simplicity, or making IPv6
more efficient and/or more useful.  To avoid making IPv6 a strict
requirement, clients for such an IPv6-only service could implement this
profile of TSP to provide a simple backward-compatible mode for IPv4-only
network nodes, without impairing all advantages of being IPv6-only.
.PP
This daemon is in fact a stateless translation between an IPv4 client
and the general IPv6 world; the interactions defined by TSP are all
handled as required by RFC 5722, but some are strictly speaking not
required for \fBpubTSP\fR.  We emphesise that their specification should still
be met in all clients, so as to avoid dependency on this one
implementation of TSP, and/or its current version.
.PP
The implementation listens to a UDP socket on TSP standard port 3653
on the IPv4 side, and to a
tunnel endpoint to capture all traffic matching an IPv6 prefix.
It basically tosses traffic back and forth between these interfaces,
but not without performing the SECURITY CHECKS desribed below
on what is tossed at it.
.SH OPTIONS
.TP
\fB\-h\fR
.TP
\fB\-\-help\fR
Print usage information and exit.
.TP
\fB\-t\fR \fI/dev/tunX\fR
.TP
\fB\-\-tundev\fR \fI/dev/tunX\fR
Instead of creating a tunnel for the duration that \fBpubTSP\fR runs,
use one that already exists and that has already been setup with
the proper IPv6 prefix.  This option makes it possible for
non-root users to run \fBpubTSP\fR.  All that is required is acccess to
the tunnel device by the user that runs \fBpubTSP\fR.  Optional on Linux.
.TP
\fB\-l\fR \fIv4addr\fR
.TP
\fB\-\-v4listen\fR \fIv4addr\fR
Bind to the given local IPv4 address and listen for incoming TSP
tunnel commands and packaged-IPv6 traffic.  Required.
.TP
\fB\-L\fR \fIv6prefix/64\fR
.TP
\fB\-\-v6prefix\fR \fIv6prefix/64\fR
Bind to the given IPv6 address range through a tunnel device, and
forward incoming IPv6 messages to IPv4-based UDP tunnel endpoints.
See ADDRESS FORMAT below for an explanation of the lower half of
the IPv6 addresses.  Required.
.PP
If no \fB\-t\fR option is given, a tunnel will be created for the time that
\fBpubTSP\fR is running, and the \fIv6prefix/64\fR is used as a router address
on that interface.  Routing table entries will not be setup by \fBpublicTSP\fR,
nor will the general ablity to forward IPv6 traffic.
.SH ADDRESS FORMAT
.PP
An IPv6 address used from \fBpubTSP\fR reveals the IPv4 address and UDP port
used by the tunnel endpoint.  This format is checked on sending from
the IPv4 tunnel to IPv6, and used to reconstruct the IPv4 tunnel access
information for traffic from IPv6 to the IPv4 tunnel.
.PP
The format of the IPv6 addresses managed by \fBpubTSP\fR are:
.PP
\fIv6prefix\fR + \fIv4addr\fR + \fIudp-port\fR + \fIlocalnet\fR
.PP
In this format, the \fIv6prefix\fR is configured with the \fB\-L\fR option,
and the \fIv4addr\fR with the \fB\-l\fR option.  The \fIudp-port\fR is noted on
arrival of a packet on the IPv4 tunnel side of \fBpubTSP\fR.
.PP
The \fIlocalnet\fR defaults to 0, but may be used to differentiate up to
65,536 different hosts accessible through the same TSP client.  As
the main application foreseen for \fBpubTSP\fR is to get IPv6-only tools and
devices working on an IPv4-only network, this is not a probable setup,
but it is nevertheless possible.  The current version of \fBpubTSP\fR does
not actually hand this over as a subnet.
.PP
The router address that \fBpubTSP\fR chooses for itself consists of the
\fIv6prefix\fR with zeroes appended; this falls outside the setup above,
because neither IPv4 addresses nor UDP port numbers are not permitted
te be zero-valued.
.PP
Incoming IPv6 traffic destined for a serviced address is first checked
as specified under SECURITY CHECKS, and then forwarded to \fIudp-port\fR at
\fIv4addr\fR.  In doing so, the IPv6 packet is embedded in whole inside
the UDP packet.  The IPv6 addresses are not altered, but only used
to derive IPv4 contact information.
.PP
Outgoing IPv6 traffic arriving on the IPv4 tunnel side of \fBpubTSP\fR will
be checked to have been sent from the right \fIv6prefix\fR and mention
the \fIv4addr\fR and \fIudp-port\fR matching the client's public side.  That
is, NAT may translate the IPv4 address and UDP port used, but these
parts of the IPv6 address should show how it is forwarded to \fBpubTSP\fR.
Note that the TSP protocol provides this necessary information at the
time the TSP tunnel is created.
.PP
It is recommended to keep NAT state in tact by regularly sending over
the UDP port to the tunnel endpoint.  At the very least, a regular
ping could do that.  Alternatively, a client-mode only daemon could
ensure that it is sending regularly during the times that an outside
party might wish to send to it.  This is under the assumption that no
explicit mapping in NAT overtakes this responsibility of an active
mapping between the internal and external address space.
.SH SECURITY CHECKS
.PP
Not everything will be passed through \fBpubTSP\fR, even if this would be
technically possible.  A few security checks are applied to silently
drop traffic that looks evil.
.PP
Packets should be long enough to at least contain the IPv6 traffic
and a minimal payload size.  Also, it should not exceed a predefined
MTU of 1280 bytes for IPv6.
.PP
IPv6 traffic uploaded through the IPv4 side should reveal the proper
IPv4 settings in the IPv6 source address, as specified under
ADDRESS FORMAT above.  This is basically the tunnel aspect of egress
filtering.
.PP
Tunnel commands should adhere to the format of RFC 5722 and may not
contain any NUL characters.
.SH BUGS
Currently, \fBpubTSP\fR does not use ICMP notifications at the IPv4
level to provide smart feedback to an IPv6 client.  It is undecided
at this point if this would add value.
.PP
To be able to fallback to this TSP profile, an IPv6-only application
needs to find a \fBpubTSP\fR or similar service.  A general naming
or numbering scheme is needed to make that straightforward.  The
\fBpubTSP\fR service could be setup privately and configured in
individual IPv6-only nodes, but it could accelerate the introduction
of IPv6-only nodes if this were organised by network providers.
.PP
Ideally, \fBpubTSP\fR would be near all heavily connected nodes
of the Internet.  There, they would improve connectivity without
being a detour for the traffic.  Alternatively, it would be located
in various uplinks.  To optimise routing, it is possible to assign
a fixed IPv4 address and IPv6 prefix for \fBpubTSP\fR running
anywhere; its stateless operation means that traffic going back and
forth can go through different instances of \fBpubTSP\fR without
posing problems.
.PP
The \fBpubTSP\fR daemon is a piece of highly efficient code,
and it should be able to handle very high bandwidths.  A stress
test has not been conducted yet.
.SH LICENSE
Released under a BSD-style license without advertisement clause.
.SH SEE ALSO
The 0cpm project is an example of an IPv6-only SIP application
that can use \fBpubTSP\fR and comparable TSP tunnel services to
demonstrate the advantages of IPv6 to end users.  It is also
a typical example of a transitionary need for something like
\fBpubTSP\fR.
.PP
http://0cpm.org/ \- the homepage of the 0cpm project.
.PP
http://devel.0cpm.org/pubtsp \- the homepage of \fBpubTSP\fR.
.PP
RFC 5722 \- the authoritative description of TSP, of which \fBpubTSP\fR is
implements a specific profile for public service under NAT traversal.
.SH AUTHOR
\fBpubTSP\fR was written by Rick van Rein from OpenFortress.
It was created to support the 0cpm project.