So my recipe for least pain is to edit cupsd.conf directly, and ignore all those goofy GUI thingies. Let's say you have two subnets, 192.168.1.0/24 and 192.168.2.0/24. You need to have routing already configured to pass traffic between the two subnets, so everyone can ping everyone. Let's say you have a printer server at 192.168.1.10, and you want computers on 192.168.2.0/24 to be able to use it. This is a complete, barebones example CUPS configuration for 192.168.1.10:

##/etc/cups/cupsd.conf
LogLevel warning

#this varies; check your distribution
SystemGroup lpadmin

# Allow remote users to access this server
Port 631
Listen /var/run/cups/cups.sock

# Enable printer sharing
Browsing On
BrowseAllow all
BrowseAddress 192.168.1.255
BrowseAddress 192.168.2.255
DefaultAuthType Basic

<Location />
# Allow shared printing
Order allow,deny
Allow 192.168.1.0/24
Allow 192.168.2.0/24
</Location>

<Location /admin>
# Only local users can access Web admin pages
Order allow,deny
Allow localhost
</Location>

<Location /admin/conf>
# Only local system users can access config files
AuthType Basic
Require user @SYSTEM
Order allow,deny
Allow localhost
</Location>

Your configuration may come with a batch of policy directives. You can leave these as they are.

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