Help to Solve a mistery

[crazy4nothing]

Scenario: Connect via Network a PC with a FTP Server to a CNC Machine name not relevant.

PC Windows 8/ Windows 7 firewall down and the FTP server with username/login and password protected and anonymous access too.
CNC Machine with a transceiver TBase10 to special cable DB25-9 Style.

And 3 routers.
1.- Asus RTN10P (brand New, newest model)
2.- Cisco-Linksys BEFSR81 (Old but Well functioning),
3.- Dlink Di-604 (new, yeah its old but brand new)

Network connection and settings.
The PC has a reserved ip address x.x.x.102
the cnc machine (unix i think as os, not user changeable, just user application at top) also reserved ip address x.x.x.101
Router Default Gateway x.x.x.1

Try:
Router 1: Did not work, ip reservation by mac, the connection could not be established, reason, CNC could not access PC (FTP SERVER)
Router 2: Did not work, same configuration as 1
Router 3: Same configuration as 1 and 2, This router works..

Now Router 2 and 3 are practically same age not properly but they a kind of old at least 10 years or more. Router 1, is new model from asus, i think firmware is linux.

Why the router 3 works? is there on the TCP/IP that is different from the router 1. What about with number 2 that are from same technology era?
Is there something in the way they reserve assign ip addresses?
is there a special feature default implemented on Dlink (router 3) that non of other implement.

Any idea would be appreciated

 

[CooCooCaChoo]

When you installed the other two routers, did you power cycle the PC and CNC machine after the router came back up? This action would clear DHCP address assignments that were handed out to the PC and CNC machine, forcing them to get a new address.