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[INFO] Network printer not detected

PostPosted: Jul 5th, '15, 11:58
by mla
Here's a very odd wrinkle which may be causing a few people some grief. I have an HP printer which has no interfacse other than wifi. It does not get automatically detected either by system-config-printer (which is what MCC->Hardware->Printing uses) nor by hp-setup (the hplip printer setup utility), despite the fact that there is no firewall on the machine. Not a big problem, since I happen to know the printer's IP address, which does the trick, but puzzling none the less.

I have now discovered, entirely by accident that both utilities do detect the printer if (a) the firewall is enabled and (b) the ethernet interface is checked off. I.e. the firewall is defined but not applied. Very odd. Probably affects all network printers and/or scanners, not just HP ones.

Re: [INFO] Network printer not detected

PostPosted: Jul 6th, '15, 10:50
by doktor5000
Or it might be that the nmap parsing is broken again :/
Maybe something similar to this one crept in again: https://bugs.mageia.org/show_bug.cgi?id=12781

Re: [INFO] Network printer not detected

PostPosted: Jul 6th, '15, 16:25
by mla
Not clear how nmap is to blame, since it *does* work under the conditions I described. As usual, though, there is yet more to it, as a bit more poking about shows.

For auto-dicsovery to work, "network services autodiscovery" must be enabled in the firewall. This may not seem surprising, until I add that this is the case whether or not the firewall is disabled! To put it otherwise, if you do not wish firewall enabled, you must still enable autodiscovery in the firewall before disabling the firewall.

Auto-discovery will also work if the firewall is enabled, but not applied to Ethernet interface(s). This is true even if having enabled the firewall (without services autodiscovery) you are still looking at the window asking you which interface(s) it should be applied to. Until you click OK to confirm applicability to your Ethernet interface(s), auto-discovery will work. Once you click OK, with Ethernet interface(s) checked, it will stop working.

Doesn't sound like an nmap problem to me. :-)

Re: [INFO] Network printer not detected

PostPosted: Jul 6th, '15, 20:19
by doktor5000
mla wrote:For auto-dicsovery to work, "network services autodiscovery" must be enabled in the firewall. This may not seem surprising, until I add that this is the case whether or not the firewall is disabled! To put it otherwise, if you do not wish firewall enabled, you must still enable autodiscovery in the firewall before disabling the firewall.

Auto-discovery will also work if the firewall is enabled, but not applied to Ethernet interface(s). This is true even if having enabled the firewall (without services autodiscovery) you are still looking at the window asking you which interface(s) it should be applied to. Until you click OK to confirm applicability to your Ethernet interface(s), auto-discovery will work. Once you click OK, with Ethernet interface(s) checked, it will stop working.


I think that should be reported as a bug against our firewall configuraton.

Re: [INFO] Network printer not detected

PostPosted: Jul 6th, '15, 22:08
by mla