Canon PIXMA MX870 - Manual (Page 1098)

set the security software to always allow access.
If using any programs that switch the network environment, check their settings. Some
programs will enable a firewall by default.
Check 14: When using a router, connect the printer and computer to the LAN
side (same network segment).
Page top
Page 1098 of 1127 pages Cannot Communicate With the Machine/Cannot Print from the Machine