Why does my wifi randomly disconnect?

Happens sporadically, in 5-20 minute intervals; as soon as I reconnect to my school's network (sometimes requires re-authentication), it works fine until the next failure.

When plugged into ethernet, there are no connection problems.

We use Cisco Clean Access servers. The authentication takes place in the web browser and requires username and password. I don't believe there is any authentication (WPA, etc.) on the connection itself.

I have run updates, and have not experienced any problems like this on other wireless networks. I run Ubuntu 11.04.

Output of sudo lshw -class network:

  *-network               
       description: Ethernet interface
       product: 82566MM Gigabit Network Connection
       vendor: Intel Corporation
       physical id: 19
       bus info: pci@0000:00:19.0
       logical name: eth0
       version: 03
       serial: 00:1f:e2:12:3c:8b
       capacity: 1Gbit/s
       width: 32 bits
       clock: 33MHz
       capabilities: pm msi bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=1.2.20-k2 firmware=0.3-0 latency=0 link=no multicast=yes port=twisted pair
       resources: irq:46 memory:fe200000-fe21ffff memory:fe225000-fe225fff ioport:1840(size=32)   *-network
       description: Wireless interface
       product: AR5001 Wireless Network Adapter
       vendor: Atheros Communications Inc.
       physical id: 0
       bus info: pci@0000:03:00.0
       logical name: wlan0
       version: 01
       serial: 00:23:4d:dc:69:3e
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress msix bus_master cap_list ethernet physical wireless
       configuration: broadcast=yes driver=ath5k driverversion=2.6.38-11-generic firmware=N/A ip=149.175.158.37 latency=0 link=yes multicast=yes wireless=IEEE 802.11bg
       resources: irq:17 memory:df2f0000-df2fffff

Solution 1:

This random disconnection could be a MTU issue - you should discuss this with your school network maintainer.

Possibly your MTU size could be 1500 or may be 1432 or some-other value your network maintainer should be able to tell you.

Normally "Automatic" is enough to establish a connection - maybe in this specific case you need a definitive value.

Look to change the MTU value in Network Manager - Edit Connections

i.e.