Here is a quick fix that might help users experiencing the “no devices available” problem when using xsane, the Linux scanning tool.
In this case, the device was an HP 3070 B611, a combined printer and scanner. The OS (Fedora 20) was able to see the device as a printer and print okay, but the scanner part did not work. Xsane just popped a small window saying unable to find device.
The fix was a change in the CUPS configuration, and it may therefore work with other versions of Linux.
Note: (19th June 2016) This article receives an unexpectedly large number of hits. If you have come here expecting something else, for example information about network scanners like nmap or Wireshark, please leave a comment to that affect and I will adjust the keyword settings. This article is about document scanners, not software to snoop your LAN.