Ping !

[Pierre 1]

OK this one could be a bit of topics but its still usefull. How can I PING an intranet? Say I have a router on IP address 64.250.111.01 (fictive address) and I have past it some PLC or PC at addresses 192.168.1.2 and .3 ... I would like to PING them. I can PING my router but how could I pass through it to "see" whats in my remote network. I use Terminal Server to connect to the PC by forwarding its com port to the good inranet IP address but is there a way I coulds "see" whats in my network. This would save me on some driving to the shop when I cannot establish comunication... I could at least "see" if anybody is alive out there.

[Jimbo 0]

hello, You have multiple problems here. - first the subnet 192.168.xxx.xxxx is not routable. - The company will not allow traffic from the internet to the intranet so the router will block all trafic that is initiated from the internet There are two possible solutions - Change the ip address of the plc to a public internet address and change the configuration of the router ( i dont see this happening) - Use a the companys VPN (virtual private network) when you dial in to the vpn it will seem as if your pc is fysically on the companys network. Greetz, Jimbo

[Pierre 1]

I already have this IP and router IN my shop. What I want to know is can I detect IF this device in on-line or does it listen.

[Jimbo 0]

ok i think i now fully understand your problem. Well u cant forward pings with a router so pinging is out of the question. What you can try is use "Telnet <Ip address> <Port No>". Use the port number you forward to your plc and if the telnet session opens the device is online. The only question is does your plc accepts a telnet session?? normally it should. Hope this helps. Greetz, Jimbo

[RichWargo 0]

Most ports will accept a connect from a telnet client. Frequently used to test port 80, which is HTTP port. If you do connect to a port not backed by a telnet server, you just talk in whatever the lingo is for the connected server application. I.E. if you telnet to port 80 and reach the HTTP server you would type in the GET statement as defined in the HTTP specification. You would get back the HTML for the web page that was requested. Can also do the same with mailserver ports, etc. Actually any port. So if you can just get a response from ANY server application on a machine, that means you can reach the machine. If you get a response from a specific port, it means that machine has a server app running against that port.

[RichWargo 0]

Oh, and Jimbo? If PINGs are not routable, how can you ping an IP address not on your ISP's subnet? I can ping microsoft.com, but I am NOT on their subnet. Most firewall/routers can only be configured to route a TCP or UDP datagram to ONE specific machine on the intranet, so you could route PINGs to one machine, but not all.

[Jimbo 0]

Hey RichWargo, you are right about microsoft.com but thats a public ip address on the internet it is unique. i did use the wrong term it should have been "u cant forward ping requests". it is impossible (to my knowledge) for a router to forward a ping request witch is directed at the ip address of the router to another ip address. Greetz, Jimbo

[Pierre 1]

Just so I can hunderstand a bit more (by the way tancks for all your good infos): When I type a url, a Server which has in "bank" where it should point, directs my request to the appropriate IP address on the Web. If I call for a Web page it will also be directing me to a port. So if I call for www.microsoft.com this server could be sending my request to something like 207.46.156.88:80 . Does everything uses ports ? (I know it is a silly question but :( ) If so then the ping command ... what port will it be directed to ? How does a ping request looks like? How is it build?