computer not seeing modem through ethernet switch

Thread Starter

xtal_01

Joined May 1, 2016
114
Back story ... I build control panels. My customer wants one that can be controlled via the internet. So, I have a plc with an Ethernet port, a touch panel with an Ethernet port and a cellular modem with an Ethernet port. I also bought a "dumb" Ethernet switch. The modem, PLC and touch panel will all plug into the switch.

The PLC will be used for controlling and sending out e-mail alerts.

The touch panel has a built in program that allows it to host (well really it fakes it) an web site (really, it just lets you duplicate the touch panel on a web page).

The plc and touch panel should have no problems talking to each other since they are from the same supplier (Automation Direct).

So, first problem ... unplugged the Ethernet cable from my computer and plugged it into the cellular modem. Typed the address given to me in the manual in Firefox and got to the modem with no problems.

Then I added the Ethernet switch ... my computer to the switch to the modem. Now I can't talk to the modem ... why?

I know the switch works (tried it between my computer and my cable modem ... works fine).

Since it was a dumb switch I figure putting it between the computer and the modem should have been a no brainer ... what am I missing ????

Using a cellular modem is the only part of this project I have not done before ... flying by the seat of my pants here. I am sure I will have a lot of learning to do in a hurry. Not even sure how to set up a network between the PLC, touch screen and cellular modem (windows seems to do all this by itself).

Thanks .... Mike
 

BR-549

Joined Sep 22, 2013
4,938
"So, first problem ... unplugged the Ethernet cable from my computer and plugged it into the cellular modem. Typed the address given to me in the manual in Firefox and got to the modem with no problems."

What device is Firefox on?
 

bogosort

Joined Sep 24, 2011
427
So, first problem ... unplugged the Ethernet cable from my computer and plugged it into the cellular modem. Typed the address given to me in the manual in Firefox and got to the modem with no problems.

Then I added the Ethernet switch ... my computer to the switch to the modem. Now I can't talk to the modem ... why?
You might need a crossover Ethernet cable from the modem to the switch.
 

Yaakov

Joined Jan 27, 2019
1,610
You might need a crossover Ethernet cable from the modem to the switch.
Most switches today are Auto-MDIX but if this is old, or super cheap then it could will be that.

My suspicion is that the modem has a little DHCP server in it with one address and maybe the switch has some management interface that grabbed it. In any case, my first impulse is addressing in some way.
 

bogosort

Joined Sep 24, 2011
427
Most switches today are Auto-MDIX but if this is old, or super cheap then it could will be that.
This was my initial thought, given that a direct connection works.

My suspicion is that the modem has a little DHCP server in it with one address and maybe the switch has some management interface that grabbed it. In any case, my first impulse is addressing in some way.
Great point, addressing is the first thing to check.
 

Thread Starter

xtal_01

Joined May 1, 2016
114
Thanks!

I am just about to start again on the project today (had to put out a few fires this morning).

I have not done any programming to the modem ... yet ... I wanted to ask questions before screwing it up.

It is a brand new switch and modem (the modem is a SmartStart by Advantech ... BB-SL30200110-X ... Industrial Cellular Router).

As I said, when I attach it directly to my computer using an Ethernet cable .... I open Firefox ... Type in the address given in the manual that comes with the modem (Default DHCP setting is192.XXX.X.X , Default NetMask 255.xxx.xxx.x) ...I come up with the modem log in page. I can then use the default password given and gt into the modem (I did this but did not change any setting yet).

I then unplug the Ethernet cable ... plug the computer and cellular modem into the switch (WIWAV WDH-5ET-DC ... Industrial Din Rail Ethernet Switch) ... open firefox and enter the same address (192.xxx.x.x) and it can not find the cellular modem.

I did test the switch (just plugged it between my computer and the switch the feed my other computers and printers off my cable modem) and it worked fine (didn't change anything ... everything found everything).

I do agree ... might be an addressing problem but I didn't know what to change or why.

My thinking was not to change anything on the computer since I know it works (I have two computers and a printer that all see each other and the cable modem ... Windows 10 set itself up ... I did not change any settings).

I thought a switch just finds and re-broadcasts ... what would I need to change (or set) so the computer can find the modem when going through the switch?

Thanks ..... Mike
 

djsfantasi

Joined Apr 11, 2010
5,829
I agree. Check addressing.

If the switch has a management address, the switch and modem may share the same default address.

If both devices are running DHCP, there could be a conflict. Independent DHCP servers will provide the same address to both devices.

Find out how each connected device gets their address. Static address assignment (with the appropriate DHCP scopes) are best for backbone equipment.

While I appreciate concern for security, providing addresses as 192.xxx.x.x isn’t helpful. In fact, if xxx isn’t 168, it is not a private network.
 

Yaakov

Joined Jan 27, 2019
1,610
Looking at the modem manual I find the default address for the httpd is 192.168.1.1 which is very likely to be a collision if the switch is managed.

Also, make sure the cable you are using works. Since you must be using one cable when going directly and two when going through the switch, the second cable needs to be vetted.

The DHCP server in the modem is a full dhcpd so there is no problem with multiple leases.
 

Yaakov

Joined Jan 27, 2019
1,610
A little further reading seems to indicate the dhcpd might not default to on.

If that’s the case, check the IP address the computer has when it is plugged into the switch and make sure it is in the 192.168.1.0 network with a netmask of 255.225.0.0 or 255.255.255.0
 

Thread Starter

xtal_01

Joined May 1, 2016
114
You don't know how much I appreciate this! As I said, 30 years of control panels but never touched a cell modem!

Sorry, don't know what I should post or not ... guess it does not matter. I do have a static IP address from Verizon. After I get it all up and running, I know I may (should) look at open VPN for security.

Yes, the PLC, the touch panel and the cellular modem all have just one Ethernet port.

So I purchased a switch: https://www.amazon.com/WIWAV-WDH-5ET-DC-Unmanaged-Industrial-Wall-Mount/dp/B07125JMRR/ref=sr_1_2?keywords=WIWAV+switch&qid=1558114794&s=gateway&sr=8-2

It is an unmanaged dumb switch (at least that is what I think I bought).

My "thinking" was a dumb switch would tie together all three units. The PLC and Panel can take with each other. The PLC can send out e-mail alerts and the Touch panel will act as the server so the client can turn his pumps on and off.

Just FYI .... All this thing does is allow the client to turn on and off 12 water pumps. There are two flow meters on site .. each give a 4-20 mA signal. I will use the PLC as a totalizer and once a day send out the flow total for the previous 24 hours. If a pump goes down (the flow falls out of limits or an overload trips or a contactor is not on when the PLC says it should be) then the PLC will also send out an e-mail.

This part of the project is my only "fear". I have not ordered the PLC is a BX-DM1E-M-D and the panel a EA9-T15CL-R .. both from Automation Direct. I would have gotten the modem off them but they didn't have one that supports Verizon and my client didn't want to change carriers.

I will plug this all back together and see what the addresses are.

Again ... thanks for all the help! I am just a one man shop (work out of the house as my wife is paralyzed from the shoulders down and needs 24/7 care). I almost turned down this job but it was from a good client who asked and I hate to turn down any work.

Thanks again .... Mike
 

djsfantasi

Joined Apr 11, 2010
5,829
Mike,

That’s better. The device I showed was the model you had previously defined as a switch. This is a dumb switch, without a DHCP server or a managed port. So there is no IP conflict between the switch and modem. Additionally, it has features such that you shouldn’t need crossover cables.

At this point, it’s important to know the IP configuration on the computer and modem.

For each device, post the following info when you’ve configured your connection as:
Computer - Switch -Modem​
I need to know:
Computer IP address
Computer Subnet Mask
Computer Gateway
Computer DHCP server
Modem IP address (internal*)
Modem Subnet Mask
Modem Gateway
Modem DHCP Server​

Plus the DHCP configuration on the modem:
DHCP Scope
DHCP Gateway
DHCP Gateway​

Note that as far as your issue is concerned, the external Verizon IP address is inconsequential. Your problem is on the internal* network (those addresses in the range of 182.168.1.nnn)

Unless you’re trying to access these devices through Verizon... but I don’t think do
 

Yaakov

Joined Jan 27, 2019
1,610
A wiring diagram with connections and the addresses would be very helpful.

Make sure you have link lights on all connected ports as well.
 
Last edited:

Thread Starter

xtal_01

Joined May 1, 2016
114
Got it!

I have been reading .. and reading ... and reading. This is why I didn't mention the static IP ... I know I will need that only for communicating on the web later.

I will connect this up and get all the information to post.

As I said, Windows magically did all this set up for me so I have never needed to learn any of these thing!

Thanks so much again!

Mike
 

Thread Starter

xtal_01

Joined May 1, 2016
114
OK ... first thing is I did connect via the switch but I am not sure why????

I tried the computer directly to them modem ... typed in 192.168.1.1 ... it brought me to the log in page (https://192.168.1.1/login.cgi)

Then I connected the switch ... typed 192.168.1.1 ... error message, could not locate.

Then I typed in https://192.168.1.1/login.cgi ... it connected!

Soooooo why did it work when I added the "login.cgi" to the address?

Once in a peaked around ... a lot information there.

I took three screen shots .... I am hoping this is the information you wanted. If not please let me know and I can take more shots.

I tried to look for my computers DHCP ... could not find it and had to disconnect from the internet so I could look up how to find it in Windows 10 I did take one screen shot of the network connection with the modem. Looking it up, I see had have to run "ipconfig /all" in the command prompt to get the computers info ... do you still want me to do this?

Sorry ... I can't easily upload a file to my web site to I added them as attachments.

Thanks .... Mike
 

Attachments

Yaakov

Joined Jan 27, 2019
1,610
OK ... first thing is I did connect via the switch but I am not sure why????

I tried the computer directly to them modem ... typed in 192.168.1.1 ... it brought me to the log in page (https://192.168.1.1/login.cgi)

Then I connected the switch ... typed 192.168.1.1 ... error message, could not locate.

Then I typed in https://192.168.1.1/login.cgi ... it connected!

Soooooo why did it work when I added the "login.cgi" to the address?
Does bare "https://192.168.1.1/" now work through the switch, and What happens when you type "https://192.168.1.1/"?

The router requires https and it could be that the bowser could be trying http only, which is on port 80, and will not respond.
 
Top