obtain IP address automatically option

[nwboson]

We all know the pain of walking up to a panel and having to guess the IP addresses used when there is no DHCP server. I couldn't agree more about the frustration.

So our panels contain an IP address label on the back of every panel door that lists all the IP addresses of each device in that panel and a listed reserved IP address for a 'debugging PC'.

And when I walk in a new environment, the Brother PTouch label printer is one of the first devices to get used.

 

[The Plc Kid]

I agree but those labels and documents are inside the cabinet and per arc flash regs here if you open the panel you have to have on your space suit. I would feel less secure posting them on the outside of the panel for everone to view so that why i defer to dhcp per port so only the locked port of the graceport works and it is locked down by mac id which we all know can be spoofed but if they know how to spoof a mac id I need them in my department anyway because they would be smarter than the guys I have.

 

[realolman]

I wish I hadn't mentioned anything about the wireless AP. It really isn't very relevant. I would like a much smaller focus.

An earlier post made the analogy to a phone and a dial tone.

I know it was analogy and not to be taken literally, but to continue on with that analogy ...

specifically , what is happening when I connect my laptop to nothing else but a single panelview that causes the laptop to display that the network is connected and at what speed, and sometimes says "limited or no connectivity " sometimes not.

How does it know how much connectivity there is?

How does it know I can't connect to the internet through the panelview?

What "dial tone" is the laptop hearing?

I would just like to know what the laptop is "saying" to, and hearing from the panelview, and yet gives me such a hard time talking to it until I discover and enter a compatible IP address.... which is often not an easy thing to discover.

 

[iant]

you need to setup the internet access in windows to 'never dial' when a LAN is detected.
Also turn your wifi off - in most cases

 

[rdrast]

I wish I hadn't mentioned anything about the wireless AP. It really isn't very relevant. I would like a much smaller focus.

An earlier post made the analogy to a phone and a dial tone.

I know it was analogy and not to be taken literally, but to continue on with that analogy ...

specifically , what is happening when I connect my laptop to nothing else but a single panelview that causes the laptop to display that the network is connected and at what speed, and sometimes says "limited or no connectivity " sometimes not.

It knows that it is connected because the wire has a signal on it. They physical layer transport doesn't know anything at all about IP addresses, or how to route traffic, it only knows that there is a transmitter/receiver pair at the other end of the wire.

How does it know how much connectivity there is?

Limited connectivity is a message from Windows telling you that there is no known DHCP partner out there to assign you an IP address, and you have your IP Configuration set for automatic addressing (DHCP). In that case, by default, this activates the "APIPA" mode in Windows, and assigns an Automatic Privite IP Address in the 169.x.x.x range.
[/quote]

How does it know I can't connect to the internet through the panelview?

Possibly because the panelview doesn't respond when something is sent to the Gateway address? A PanelView isn't a gateway, and it doesn't handle DNS operations. Any time you try to access an address that isn't on your local network and subnet, the request is forwarded to the gateway address. It is up to the gateway router to handle sending the request up to the higher level network.

I would just like to know what the laptop is "saying" to, and hearing from the panelview, and yet gives me such a hard time talking to it until I discover and enter a compatible IP address.... which is often not an easy thing to discover.

Get used to it. If you don't know the address, you can't talk to the device. If you don't know the address, you can't mail a letter. If you don't know the John's phone number, you can't place a call to him. What exactly is so difficult to understand? A network isn't a point to point connection like (most) RS-232 serial connections are.

Forget Ethernet, you still need to know the node addresses for every other network out there if you want to use them, ControlNet, Profibus, Modbus...and many others.

Why not start reading up on some of the basics first, and then come back with questions?
http://www2.cit.cornell.edu/computer/support/subsubnetting.html

http://en.wikipedia.org/wiki/IPv4

http://www.howstuffworks.com/internet/basics/question549.htm

 

[realolman]

Thank you for your answers ... there was some good info there. I'm sorry you were irritated by my questions. I really don't think you need to be.

Perhaps in the future when we are in the situation of having a panelview or PLC that requires some modification or repair, instead of a dumbbell like me attempting to correct it, you could drop by.

It knows that it is connected because the wire has a signal on it. They physical layer transport doesn't know anything at all about IP addresses, or how to route traffic, it only knows that there is a transmitter/receiver pair at the other end of the wire.

that is one of the things I want to know. How does it know the wire has a signal on it? what kind of a signal? what hardware detects that and how?

 

[The Plc Kid]

Realolman

If you are physically connected and you get a " limited or no connectivity " then this means it does not see the internet.

How does it know you ask? It is a service in Win vista,win 7, called NCSI which stands for Network Connection Status Indicator and it works with a few other service but for your understanding when it see's a physical connection this service tries to connect to www.msftncsi.com, then requests http://www.msftncsi.com/ncsi.txt. This file is a plain-text file and contains only the text

If that fails then it sends a DNS lookup request for dns.msftncsi.com. This DNS address should resolve to 131.107.255.255. If the address does not match, then it is assumed that the internetconnection is not functioning correctly.

 

[The Plc Kid]

Try the links. The server will deny you because you are using the wrong port but the text file will show it's header.

 

[The Plc Kid]

If you don't want NCSI you can disable it in the registry.

Also if you don't want your machine to contact microsoft from everywhere you connect to the internet you can run your own NCSI server at home and point your laptop to it.

This is done quite frequently in the black hat community.