If I switch on my router after I've booted into KDE I'd expect the network connection to be enabled automatically, but it isn't.

Both ifconfig and Network Settings don't even see the wired interface (it is greyed out in Network Settings).

I've tried many things including restarting the network service but the only solution seems to be to reboot.

On a similar note if the network is disconnected during a session, and then reconnected, the connection does not restore - though it might do after a very long delay but I'm not sure what the trigger is.

My netbook has no such problems. Does anyone know of any settings I can adjust which will prevent this?

Have a look at output of "ifconfig -a" to see if the interface is being detected correctly. This looks like a issue in NetworkManager itself.

If I run "ifconfig -a" after booting with the router powered OFF the interface "eth0" is not detected, just loopback.

Subsequently powering on the router makes no difference, only a reboot will cause "eth0" to be listed using "ifconfig -a".

I added a wired connection in Network Connections and repeated the test but this did not make any difference.

This looks like a driver problem or something blocking the network interface. Which ethernet card (lspci) and distribution do you use?

It's a Realtek RTL8111/8168B PCI Express Gigabit Ethernet controller on Kubuntu.

does dmesg shown any message reggarding eth0 interface? Which kernel version do you use?

Hello lamarque,

Thank you for your help working through this.

Kernel is 2.6.38-11-generic

If I boot the machine without a live network connection dmesg shows no message regarding eth0, in fact the network interface driver is not loaded at all - effectively the interface is invisible.

Compare this to when I boot with a live network connection - I see these references in dmesg:

r8169 Gigabit Ethernet driver 2.3LK-NAPI loaded
r8169 0000:04:00.0: PCI INT A -> GSI 17 (level, low) -> IRQ 17
r8169 0000:04:00.0: setting latency timer to 64
r8169 0000:04:00.0: irq 44 for MSI/MSI-X
r8169 0000:04:00.0: eth0: RTL8168c/8111c at 0xffffc90000c74000, 00:1f:d0:23:31:f5, XID 1c4000c0 IRQ 44

Plus some later messages when it brings up the eth0 link.

Ok I have now resolved this issue, thanks (especially to lamarque) for help in troubleshooting.

There is a 'Green LAN' setting in my PCs BIOS which will automatically disable the controller when a LAN cable is not detected, this was enabled, I have now disabled this setting - simple as that!

Thanks again.