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TAP.md

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Thundergate TAP Driver

The Thundergate toolkit includes Python modules inplementing a PCI driver for Broadcom 57xx devices, and a TAP interface driver consuming it. Together they comprise a userspace interface between the network hardware and the kernel TCP/IP stack.

This functionality is available on Windows and Linux subject to the caveats described in the platform-specific INSTALL files.

Usage

Specify -d on the command line to start the execution of the driver. The driver runs in the foreground and offers a minimal single-key interface.

# python py/main.py -d
.
.
. 
[+] produced 128 rx buffers
[+] enabling transmit mac
[+] enabling receive mac
[+] configuring led
[+] waiting for interrupts...
[+] detecting link
[+] full duplex gige link negotated (res: 0000ff3c, txpause: False, rxpause: False)

d - link detect
h - help
q - quit
s - dump statistics
r - reset statistics
v - toggle verbosity

Notes

  • The TAP interface created will assume the next available device name on the host system, e.g. 'tapX' on Linux, or "TAP-Windows Adapter #X". It should only persist for the life of the process, but the cleanup code is in finally blocks, so crashed processes might leave behind dead interfaces requring manual removal (especially on Windows).

  • The TAP device will bring itself up and down based on the state of the link, but may need IP configuration using host OS tools (such as Linux's ip or ifconfig, or Windows's ipconfig or ncpa.cpl.)

  • Link detection and change notifications are hit-and-miss and may not trigger at startup. Press d to force link re-negotiation.

  • The TAP driver relies on asyncio from Python 3, as backported to Python 2 by the 'trollius' package (pip install trollius). This package has since been deprecated without replacement, although it continues to work.

Performance

Performance was measured using iPerf3 over a point-to-point Cat5 cable connecting a MacBook Air running Debian 8 and a MacBook Pro running Windows 10. All compilation was performed without optimization and the standard CPython 2.7 interpreter was used. These (now outdated) numbers are only meaningful relatively (if even).

Server: Windows 10 w/ b57nd60a
Client: Debian 8 w/ tg3
Result:

[ ID] Interval           Transfer     Bandwidth       Retr
[  4]   0.00-10.00  sec   950 MBytes   797 Mbits/sec    0             sender
[  4]   0.00-10.00  sec   949 MBytes   796 Mbits/sec                  receiver

Server: Windows 10 w/ b57nd60a
Client: Debian 8 w/ Thundergate TAP
Result:

[ ID] Interval           Transfer     Bandwidth       Retr
[  4]   0.00-10.00  sec   151 MBytes   127 Mbits/sec    0             sender
[  4]   0.00-10.00  sec   150 MBytes   126 Mbits/sec                  receiver

Server: Debian 8 w/ tg3
Client: Windows 10 w/ Thundergate TAP
Result:

[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-10.02  sec  11.8 MBytes  9.84 Mbits/sec                  sender
[  4]   0.00-10.02  sec  11.8 MBytes  9.84 Mbits/sec                  receiver

Server: Debian 8 w/ Thundergate TAP
Client: Windows 10 w/ Thundergate TAP
Result:

[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-10.01  sec  17.1 MBytes  14.4 Mbits/sec                  sender
[  4]   0.00-10.01  sec  16.9 MBytes  14.2 Mbits/sec                  receiver