2010-04-17 02:45:12 +02:00
|
|
|
|
|
|
|
|
Tor's (little) Firewall Helper specification
|
|
|
|
|
Jacob Appelbaum
|
|
|
|
|
|
|
|
|
|
0. Preface
|
|
|
|
|
|
|
|
|
|
This document describes issues faced by Tor users who are behind NAT devices
|
|
|
|
|
and wish to share their resources with the rest of the Tor network. It also
|
|
|
|
|
explains a possible solution for some NAT devices.
|
|
|
|
|
|
|
|
|
|
1. Overview
|
|
|
|
|
|
|
|
|
|
Tor users often wish to relay traffic for the Tor network and their upstream
|
|
|
|
|
firewall thwarts their attempted generosity. Automatic port forwarding
|
|
|
|
|
configuration for many consumer NAT devices is often available with two common
|
|
|
|
|
protocols NAT-PMP[0] and UPnP[1].
|
|
|
|
|
|
|
|
|
|
2. Implementation
|
|
|
|
|
|
|
|
|
|
tor-fw-helper is a program that implements basic port forwarding requests; it
|
|
|
|
|
may be used alone or called from Tor itself.
|
|
|
|
|
|
|
|
|
|
2.1 Output format
|
|
|
|
|
|
|
|
|
|
When tor-fw-helper has completed the requested action successfully, it will
|
|
|
|
|
report the following message to standard output:
|
|
|
|
|
|
|
|
|
|
tor-fw-helper: SUCCESS
|
|
|
|
|
|
|
|
|
|
If tor-fw-helper was unable to complete the requested action successfully, it
|
|
|
|
|
will report the following message to standard error:
|
|
|
|
|
|
|
|
|
|
tor-fw-helper: FAILURE
|
|
|
|
|
|
|
|
|
|
All informational messages are printed to standard output; all error messages
|
2010-09-24 21:52:07 +02:00
|
|
|
are printed to standard error. Messages other than SUCCESS and FAILURE
|
|
|
|
|
may be printed by any compliant tor-fw-helper.
|
|
|
|
|
|
|
|
|
|
2.2 Output format stability
|
|
|
|
|
|
|
|
|
|
The above SUCCESS and FAILURE messages are the only stable output formats
|
|
|
|
|
provided by this specification. tor-fw-helper-spec compliant implementations
|
|
|
|
|
must return SUCCESS or FAILURE as defined above.
|
2010-04-17 02:45:12 +02:00
|
|
|
|
|
|
|
|
3. Security Concerns
|
|
|
|
|
|
|
|
|
|
It is probably best to hand configure port forwarding and in the process, we
|
2010-09-24 21:52:07 +02:00
|
|
|
suggest disabling NAT-PMP and/or UPnP. This is of course absolutely confusing
|
|
|
|
|
to users and so we support automatic, non-authenticated NAT port mapping
|
|
|
|
|
protocols with compliant tor-fw-helper applications.
|
|
|
|
|
|
|
|
|
|
NAT should not be considered a security boundary. NAT-PMP and UPnP are hacks
|
|
|
|
|
to deal with the shortcomings of user education about TCP/IP, IPv4 shortages,
|
|
|
|
|
and of course, NAT devices that suffer from horrible user interface design.
|
2010-04-17 02:45:12 +02:00
|
|
|
|
|
|
|
|
[0] http://en.wikipedia.org/wiki/NAT_Port_Mapping_Protocol
|
|
|
|
|
[1] http://en.wikipedia.org/wiki/Universal_Plug_and_Play
|
