On Sat, 2014-10-11 at 21:26 -0400, Kevin Cummings wrote:
When I started the Print Settings tool, I had to unlock it first,
then
I started the ADD PRINTER dialogue. When it prompted to select
device, I opened the Network Printer expansion, but the printer I was
looking for was not present, so I decided to enter it manually. While
I was trying to figure out how to do that, an entry for the printer
"magically" appeared in the network list! I guess it took a little
time to "find" it.
My experience with these kind of things (auto discovery of things on a
network), is that there is nearly always some sort of delay (either
you're waiting for periodic announcement of available things on the net,
or waiting for things to reply to a request of what's out there), but I
have never managed to find anything that defines what the delay will be,
nor why? Was it simply call and response time (didn't seem likely, as
the period could be a few seconds to minutes), or was there a periodic
announcement, with a random or defined period?
With CUPS, at least, it was necessary to have a hole in your firewall to
receive these announcements (the IPP *service* needed to be allowed).
I'd imagine a similar requirement for ZeroConf, Avahi, or any other
auto-discovery process. It's all peer-to-peer, not run by a central
server (unless you're using Samba, which has a semi-random server), so
you have to have a hole open and waiting, all the time.
If there was a central server, you wouldn't need to, your client would
make a request, and get a reply. That reply would be *related* to your
query, and would (should?) automatically make it back through your
firewall, without requiring special configuration (normal firewall
configuration is to *allow* *related* traffic through).
--
tim@localhost ~]$ uname -rsvp
Linux 3.16.3-200.fc20.i686 #1 SMP Wed Sep 17 23:07:44 UTC 2014 i686
All mail to my mailbox is automatically deleted, there is no point trying
to privately email me, I will only read messages posted to the public lists.
George Orwell's '1984' was supposed to be a warning against tyranny, not
a set of instructions for supposedly democratic governments.