scp and rsync stall when transferring from Ubuntu hardy heron 8.04

[dennisn]

I wish someone could tell us what "Jaunty" did to "fix" this problem. I don't use Ubuntu, but I probably have this problem? It's REALLY annoying.

For me, I seem to have gotten it working by changing those aforementioned sysctl's AND changing my network device MTU's to 2200 (nothing lower seemed to work; (ifconfig wlan0 mtu 2200))

But I still don't feel satisfied -- not only don't I know what the problem was, but the "solution" seems like a hack :\.

[dennisn]

My dissatisfaction was proven correct. After rebooting my client, (and possibly restarting the network interface on the server too), I can't get it to work, even following the same steps as before, which did seem to work. Aaaarrrrgggghhhh.

Here are some clips of an earlier tcpdump I took during the stall, maybe someone can see something informative:
http://dennisn.dyndns.org/guest/pubstuff/scp-stalls/

[michelino80]

Hi all, this thread is pretty old, but the problem may still be around, as, at least for me, it is not caused by ubuntu itself.

Basically, every "hop" between you and the server will open and re-incapsulate the packets and with the incorrect mtu settings, they will never reach the destination.

The list of MTUs between you and the destination (ie: your MTU, the MTU of your access point, the MTU of your modem, the MTU of all the exchange routers until the destination, ..) should be a monotonic increasing function, for the packet to arrive at your destination.

Put in other words, this is a sequence of MTU settings that will work:
1) your network card MTU: 1492
2) your access point MTU: 1492 or 1500
3) your modem MTU: 1500

This is a sequence of MTU that will NOT work:
1) your card MTU: 1500
2) your access point MTU: 1492
3) your modem MTU: 1500

as all the packets will be discarded between 1 and 2. I had X on my operating system, 1500 on my access point and 1492 on my modem, and speedtest.net was not working in upload. I changed my access point to have a 1492 MTU and now everything works fine.

I hope this may help someone.

cheers
mic

[dennisn]

as all the packets will be discarded between 1 and 2. I had X on my operating system, 1500 on my access point and 1492 on my modem, and speedtest.net was not working in upload. I changed my access point to have a 1492 MTU and now everything works fine.

I think that's a different problem. With this bug, transfers do begin, but stall. It's been a long time since I last saw it (perhaps it's already been fixed in the kernel or something), but it only happened on my LAN with fast ethernet transfers.