On Sunday 15 April 2007 02:03, Mike Bird wrote: > On Saturday 14 April 2007 15:02, Alan Chandler wrote: > > The problem I have is this. I have a linux desktop (machine D) > > siting on a LAN in my home. This is connected to a linux > > firewall/nat router (machine S) with two ethernet cards. One links > > out to the internet, the other connects to the internal lan. > > Connections to the internet from machine D go through machine S, > > which acts as a NAT translation. I do all the control and > > firewalling using IPTABLES in machine S. > > > > Downloading a video from youtube onto Machine D's desktop I get a > > download speed of about 7Kbytes/sec. Which is very low. If I try > > to download the same one by ssh'ing into mahcine S and running wget > > on the same url, I get a download speed of 80Kbytes/sec (ie more > > than 10 times faster). > > Alan, > > I would try wget on machine D to verify that the problem is network > rather than your browser on D. If that doesn't answer your question > I would run wireshark (or tshark from the command line) for a few > seconds while machine D was downloading via S, being sure to capture > on all interfaces. The result will show what is happening to packets > trying to cross S.
Thank you for all the people who did respond to this. Just to say I AM USING wget for this. However, the suggestion to run wireshark was important because I think it is giving me a clue of the problem. This will need a TCP expert to help me - I think the problem seems to be in the sequence numbers. Let me try and explain. (wireshark is running on the gateway originally was looking on all interfaces - but this didn't help - so I limited it to the WAN interface) Firstly the case of direct downloading from my gateway. This is a summary of a three protocol exchanges using wireshark youtube->me http continuation seq 189688 next seq 191136 youtube->me http continuation seq 191136 next seq 192584 me->youtube tcp ack seq no 192584 youtube->me http continuation seq 192584 next seq 194032 Now when I look at a similar exchange when I am using the gateway machine just as a hop and there is a machine behind the gateway I get a different pattern youtube->me http cont seq 4344 next seq 5792 me->youtube tcp ack seq 5792 youtube->me http cont seq 7240 next seq 8688 me->youtube dup ack seq 5792 youtube->me http cont seq 10136 next seq 11584 me->youtube dup ack seq 5792 youtube->me http cont seq 5790 next seq 7240 me->youtube tcp ack seq 8688 youtube->me http cont seq 8688 next seq 10136 As you can see, in this case, it appears that some packets are being lost and have to repeated via a dup ack. One can presume that youtube is actually sending the packets since it is clear in the earlier case that it does so (and pretty quickly too), so I think it might come down some reason that the packets are getting dropped before wireshark sees them. I have an IPTABLES firewall, but I can't see why that should effect things. Can someone tell me a) Whether wireshark sees the packets before they are processed by IPTABLES? b) what other reason could I have for lost packets? -- Alan Chandler http://www.chandlerfamily.org.uk -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
