Computer networks and Ethernet - Notes and tools

OS Windows network tools

The software utilities listed below are always contained in OS Windows and can be launched, for example, from the command prompt. If launched without any parameter, or with /? parameter, then the optional help is displayed. HOSTS file:

There is a text file hosts (without extension) in /Windows/system32/drivers/etc/ folder. This file contains IP address mapping to host names. There is a possible of specify names for IP address manually. In this file there is always a row:

The universal address 127.0.0.1 always specifies this current computer. This address can also be replaced by the word localhost. It is useful to edit this file manualy if you have the IP adress (e.g. 121.47.0.15) of another computer that has no name in the current network. If the following row is entered into this file, then the computer can be adressed by name (e.g. promotic2):

Connection Limit - open connections limit

The open connections limit was introduced into OS Windows XP sp2 and 2003 sp1a and then cancelled in OS Windows Vista sp2 and higher. The following text is relevant for OS Windows with active connection limitation. It limits the open connection requests number to 10, in order to protect your system from malware (malicious software) infiltration and spreading all around the network. If you want to check whether your system has reached such connection limit, then take a look in OS Windows event viewer (hit start->run and enter Eventvwr.msc). Click the System item, take a look at the EventID column. If the number 4226 is being displayed, then your system has reached the connections limit. This connection limit may prevent the PROMOTIC application from proper function. For example if you communicate simultaneously with ten or more PLCs via Ethernet (see Type of communication and data sharing in PROMOTIC application), then the connection limit is reached.