Bittorrent and NAT

[David Jenkins]

On Thu, 14 Oct 2004 09:56:44 +0100 (BST), Jonathan Belson
<jon at witchspace.com> wrote:
> You can certainly download without port forwarding, but (according to
> the azureus documentation) your download speed will be limited if
> other machines can't connect to you.
> 
> When you're downloading, do you get a yellow smiley or a green one?
> Green smileys mean that you can be connected to from outside, and
> (in theory) you should get better transfer rates.

Hrmm, I get a green smiley even when no-one is uploading of me !?

As a side note, I've tried a lot of bit torrent clients and to date,
Azureus is by far the best - in terms of the interface as well as (and
more importantly) the speed.

I'd definitely persist if you do plan on using bit torrent.

If it helps, here's part of my netstat output from Windows.

TCP    127.0.0.1:6880         0.0.0.0:0              LISTENING
TCP    192.168.0.10:139       0.0.0.0:0              LISTENING
TCP    192.168.0.10:1234      62.169.210.235:6884    ESTABLISHED
TCP    192.168.0.10:1323      62.234.41.185:6881     TIME_WAIT
TCP    192.168.0.10:1334      217.225.8.8:6882       ESTABLISHED
TCP    192.168.0.10:1336      64.83.231.175:27272    TIME_WAIT
TCP    192.168.0.10:1337      66.215.49.4:5000       TIME_WAIT
TCP    192.168.0.10:1345      64.70.10.83:80         TIME_WAIT
TCP    192.168.0.10:1355      67.171.218.118:65535   TIME_WAIT
TCP    192.168.0.10:1357      64.109.30.200:6895     TIME_WAIT
TCP    192.168.0.10:1359      217.165.248.240:6881   TIME_WAIT
TCP    192.168.0.10:1361      150.101.101.71:6881    TIME_WAIT
TCP    192.168.0.10:1367      212.56.109.202:6881    TIME_WAIT
TCP    192.168.0.10:1374      202.72.180.190:6881    TIME_WAIT
TCP    192.168.0.10:1388      67.119.9.219:24861     SYN_SENT
TCP    192.168.0.10:1389      80.223.238.122:6881    SYN_SENT
TCP    192.168.0.10:1390      200.49.224.3:6885      SYN_SENT
TCP    192.168.0.10:1391      218.186.234.82:302     SYN_SENT
TCP    192.168.0.10:1392      66.239.121.238:65000   SYN_SENT
TCP    192.168.0.10:1395      156.34.223.182:6881    TIME_WAIT
TCP    192.168.0.10:1397      129.177.55.236:6881    TIME_WAIT
TCP    192.168.0.10:6881      66.245.216.185:1380    LAST_ACK
TCP    192.168.0.10:6881      68.61.178.166:4076     TIME_WAIT
TCP    192.168.0.10:6881      81.36.133.175:3301     TIME_WAIT
TCP    192.168.0.10:6881      203.148.253.25:3037    TIME_WAIT
TCP    192.168.0.10:6881      203.148.253.25:3189    TIME_WAIT
TCP    192.168.0.10:6881      203.148.253.25:3283    TIME_WAIT
TCP    192.168.0.10:6881      203.148.253.25:3373    TIME_WAIT
TCP    192.168.0.10:6881      203.148.253.25:3671    TIME_WAIT
TCP    192.168.0.10:6881      203.148.253.25:3749    TIME_WAIT
TCP    192.168.0.10:6881      203.148.253.25:3998    TIME_WAIT
TCP    192.168.0.10:6881      203.148.253.25:4120    TIME_WAIT
TCP    192.168.0.10:6881      203.148.253.25:4354    TIME_WAIT
TCP    192.168.0.10:6881      203.148.253.25:4436    TIME_WAIT
TCP    192.168.0.10:6881      216.155.79.48:1893     ESTABLISHED

Note that I am not forwarding port 6881 through my router.

As an experiment I tried the following from an external box to my home box.

$ telnet unixusers.co.uk 6881
Trying 82.133.118.138...
Connected to unixusers.co.uk.
Escape character is '^]'.

So my router is somehow letting traffic through on 6881 even though I
haven't asked it to ... !

As a precaution I just tried telnetting the netbios port (139) to see
if my router was somehow misbehaving ... thankfully it wasn't, and the
connection to that port timed out.

As a further test I opened up a random high port and tried telnetting
to that but that failed also.

So I'm not sure why my router is letting through inbound traffic to 6881.

Anyway, I just checked my routers forwarding and it appears it has
just created some rules (since I opened Azureus !)

82.133.118.138  192.168.0.10  	tcp  	6881  	
82.133.118.138 	192.168.0.10 	udp 	6881 	
82.133.118.138 	192.168.0.10 	tcp 	6969

So that's why it's working ... !

After I closed Azureus those rules dissapeared from my port forwarding list ... 
(Anyone got any ideas on that ``intelligent port forwarding'' ?)

Sorry, that doesn't really help you though.

David