[sane-devel] FIXED: network scanning quit working -- and a related question

[Alexander Pevzner]

Hi Perry,

On 12/5/20 12:48 PM, Perry Hutchison wrote:
> After power-cycling the device, it reported that its IP address had
> changed back to 192.168.0.10, and it is now found:
> 
>    $ scanimage -L
>    device `pixma:MF4800_192.168.0.10' is a CANON Canon i-SENSYS MF4800 Series multi-function peripheral
> 
> Question:  Since link-local addresses in 169.254.0.0/32 seem to be
> every bit as local as addresses on the local subnet, would it make
> sense for SANE to search for networked scanners on 169.254.0.0/32
> in addition to the local subnet?

The short answer is "no".

The long answer follows.

1. Actually SANE doesn't search for devices by itself. Devices are 
discovered by Avahi, SANE only uses result of this discovery.

2. There is no other effective method to search for scanners and other 
devices on LAN, except what Avahi does (sending discovery multicasts, 
gathering replies and so on). Brute-force scanning all addresses in the 
range is very ineffective, generates a lot of network traffic and may 
even cause some devices, connected to that network, to hung.

3. Avahi actually does its work well. But there are many things that 
affects discovery. For example, if device is not reachable due to 
routing configuration, it will not be discovered.

4. This case is DHCP failure. SANE makes reasonable assumption that 
network infrastructure is properly configured. It is not (and should be 
not) a part of SANE responsibility to workaround network infrastructure 
miss-configuration.

-- 

	Wishes, Alexander Pevzner (pzz at apevzner.com)