Destination host unreachable

[Support]

> I'm getting this when trying to ping any host on my network 
> from machine B.
> 
> Which leads me to suspect a problem with my ethernet card. 
> yet it ifconfigs up and down OK.
> 
> Is there a conclusive test to demonstrate that the problem is 
> with the network card?

Ping your network card.  Not the Loop address, but the network
address.  If you can ping the network address then you should be able
to ping the gateway or other systems on your network.