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Computer networks and Ethernet - Notes and tools

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

Windows OS network tools

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

>ipconfig /all ... Displays IP protocols and Ethernet adapters configuration.
>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 www.google.com ... 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 the extension) in the "/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 address 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 address (e.g. of another computer that has no name in the current network. If the following row is entered into the 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 Windows OS XP sp2 and 2003 sp1a and then cancelled in Windows OS Vista sp2 and higher. The following text is relevant only for Windows OS 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 Windows OS 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 PLC devices via Ethernet (see Type of the communication and data sharing in the PROMOTIC application), then the connection limit is reached.
the 1st solution of this problem is to set following Ethernet parameters in the PmaComm object: Not connect until first transfer and Close connection after every transfer so that 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 usually better not to set Close connection after every transfer, but to call the ClosePort method after the required number of messages is completed.
2nd you can solve this problem by using a 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.
PROMOTIC 9.0.28 SCADA system documentation MICROSYS, spol. s r.o.

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- Computer networks and Ethernet - Notes and tools
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