Computer networks and Ethernet - Notes and tools

This chapter contains information about computer network maintainance and configuration. We welcome all suggestions for refining a replenishing of this topic.

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.
>ipconfig /all ... IP protocols and Ethernet adapters configuration overview.
>route print ... Displays and processes network routing tables
>arp -a ... Displays and configures IP to MAC (physical) adress translation table. This table is used by the ARP protocol.
>tracert ... Reports detailed information regarding the specific points on the path to the network target.
>netstat ... Displays current network connections and TCP/IP statistics.
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: localhost
The universal adress 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. 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): 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, take a look in OS Windows event viewer. (hit start->run and enter Eventvwr.msc). Click the System entry, 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 system 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.
1. the solution of this problem is to set following Ethernet parameters in PmComm object: Not connect until first transfer and Close connection after every transfer so every transmission connects, transfers the data and closes the connection. You can achieve lower connection number (less than 10) this way, but the transfer rate may be reduced. It is often better not to set Close connection after every transfer, but to call the ClosePort method after the required number of transmissions is completed.
2. you can solve this problem by using a software utility for increasing the number of simultaneous connections (e.g. from 10 to 50). This kind of software is available on the Internet, for example:
- "xp-AntiSpy".
- it is possible that the "TCP Optimizer" may help.
- and others.
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