The router firmware has no consequence itself, excepting it might install its own firewall (and you would of course be in trouble) or set some dhcp or bootp request at boot time, requiring, as i said before, appropriate broadcasting rules.
Please check the administration page of you router for specific settings.
An obvious reason of failure would, of course, be e.g. your router now running dhcp and not assigning any more static lan ip, or your lan range there not fully allowed (specify any of its ip or mac if needed).
I rebooted cis v5 and my laptop, i had to write some new rules, but everything works fine on both sides even after rebooting both sides.
Note in this regard that, if you actually want to browse a computer from the other, you must have at least a windows shared partition and appropriate credentials.
Also note that, during the process, spoolsv prompted me for several defense+ requests, all of them blocked without remembering, and not keeping things to work.
A report of the configuration if it might help.
-The cis 5 computer is a win xp sp3 pro computer.
-cis 5 is proactive
-defense+, altough not relevant here because not saying anything excepting the spoolsv story, is paranoid.
The sandbox is disabled (and every of its settings unchecked).
Everything is checked in the monitoring settings.
Image execution is enabled, but the cloud is disabled, and nothing is allowed as a safe application, unknown applications being seen as unsafe.
-the firewall is set to advanced mode, highest level, everything checked but ics, but no rule created for safe applications.
In this configuration, all of my computers have static ip, dhcp is disabled, and the desktop is 192.168.0.40 while the laptop is 192.168.0.30, both are gateway to the router at 192.168.0.1.
Nothing but icmp blocking in global rules.
A lan zone is created 192.168.0.1-192.168.0.255, and also a netbios port rule (137-139)
Every single rule in the firewall is custom except comodo (outgoing only).
The following rules are needed for pc1 (192.168.0.40) make the symetric ones for pc2 if running cis:
-svchost:
-allow tcp or udp, both, from (lan) to (lan), source and dest ports any
(same for loopback zone)
-system (with rules for access on both sides):
-allow tcp or udp in from 192.168.0.30 to 192.168.0.40, source ports any, dest ports (netbios)
-allow tcp or udp out from (lan) to 192.168.0.30, source ports any, dest ports (netbios)
-allow udp out from (lan) to 192.168.0.255, source ports (netbios), dest ports (netbios) (note the broadcasting request).
If now you want to browse pc2 from pc1, you must also write:
-explorer:
-allow tcp out from 192.168.0.40 to 192.168.0.30, source ports any, dest port 135.
My laptop (running kerio) has fancy rules for 3G connexion, but not relevant here:
-system:
allow udp out, from any ip to 255.255.255.255, port 138 to port 138
-dhcp:
allow udp, both, from any ip to any ip, port 68 to port 67.
Note the broadcasting and bootp rules, the system does not connect anywhere if the latter is not allowed.