Ubuntu 12.04.1 with all updates installed. Laptop Lenovo Thinkpad X230 with Intel Corporation Centrino Advanced-N 6205.
WiFi sometimes becomes extremely slow. Often this occurs when I wake the system from suspend and connect to a different network. I find no obvious clues in system logs.
/etc/init.d/network-manager restart doesn't help, but a reboot does. How can I go on with debugging this issue? In specific, which parts of the system should I try to restart (without a complete reboot)?
I know of problems with Intel WiFi (see for example this question and the instructions here), but if that was the problem, I would expect the WiFi to be slow at all times, and not just sometimes. Also, I have a gut feeling that it might be a DNS issue (for example, getting a page from a known server is faster than accessing a new server), but I don't know how to tackle it.
Update: despite numerous updates in the meanwhile, I still observe this behavior. It happens always when I access my WiFi router at home after returning from work; when I reboot my laptop, the connection speed is good again.
EDIT: I have found the problem! While at work, I use a Cisco-compatible VPN client to connect to intranet (without it, I only have Internet access); package
vpnc. The problem appears if and only if I turn on VPN at work, put the computer to sleep, and wake it at home. The vpnc client does not run any longer, but apparently some configuration still lingers (I will dive into that over the next weeks). When at home and I run another vpn connection, and then disconnect with
vpnc-disconnect, my problem disappears. The
11n_disable option has no influence on this behavior.
I thank both contributors with an upvote, but -- sorry -- not with the bounty. However, the bounty is still to have for the person who will either explain to me what is happening or give me a guide how to debug the vpnc problem.