To access IPP-over-USB printer: Emulate remote machine in the network

[Till Kamppeter]

On 01/21/2017 09:56 AM, TJ wrote:
> On 16/01/17 18:05, Till Kamppeter wrote:
>> In the beginning I used localhost:60000 which makes polling capabilities
>> and status, printing, and web interface work, but the printer could not
>> be Avahi-broadcasted and so CUPS and cups-browsed could not discover it.
>>
> Possibly not the ideal solution but did you test whether using
> avahi-daemon.conf's "deny-interfaces=" with a single interface name that
> it is safe to ignore (a throw-away dummy interface) would work?
>
> I ask because the man-page for avahi-daemon.conf seems to imply that the
> interface default action is to ignore 'lo' and any point-to-point
> interfaces, but if using "deny-interfaces=" without any
> "allow-interfaces=" it will use all interfaces not specified - which
> implies that it would then use 'lo'. E.g:
>
> # allow-interfaces=
> deny-interfaces=dummy0
> # implication is that 'lo' will be used
>
> If the functionality is only required for the localhost's CUPS service
> this might be sufficient.
>
>
>

I have done some testing, modifying the avahi-daemon.conf as described, 
restarting avahi-daemon, and running avahi-discover to see which 
services get broadcasted on which interfaces. The "lo" interface did not 
appear, also not after running

sudo ip link set lo multicast on

This should activate multicast support on lo if this is possible (at 
least "ifconfig" shows the activated multicast flag).

It seems that lo does definitively not have broadcasting support, as

sudo ip link set lo broadcast 127.255.255.255

errors with "Invalid argument".

See also

http://serverfault.com/questions/554503/how-do-i-add-a-broadcast-ip-to-the-loopback-interface-under-os-x-using-ifconfig

http://serverfault.com/questions/421389/how-to-add-a-broadcast-address-to-loopback-with-ifconfig-on-a-os-x

So it looks like that we need to work with an extra interface (dummy0 
with IPv6) and find a way to let Avahi broadcast the interface's own 
host name or the interface's IP address instead of the system's host 
name or we need a way to make ippusbxd emulate a remote host with its 
own host name and IP address but not creating a virtual machine, if this 
would be possible.

    Till