All you need to make this work are a central Linux/CUPS printer server, and one Linux PC per subnet to act as a relay printer server.

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 your CUPS 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>

Next: Setting Up the Relay PC »