computer not seeing modem through ethernet switch

Thread Starter

xtal_01

Joined May 1, 2016
118
OK .. got everything ... but something strange (so what else is new) ...

In firefox (and I tried this with chrome also) ... put in the address only ... nothing. Put in the address plus the login.cgi ... it works. Then I can put in the address only and it will work! I unplugged the modem and tried this twice more. The first time with the address only, it will not find the modem, I must add the login.cgi. After if finds it once, it does not matter!

I have the screen shots of both and the screen shots of the computer network with and with out the switch.

Man I have a lot to learn !!!!!!!!!!

Thanks .... Mike
 

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eetech00

Joined Jun 8, 2013
2,302
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
Hint....The PC to Modem connection works. That means the modem (router) is either using a crossover cable, or supports auto MDI.
I didn't see in the modem spec any mention of auto MDI.

So...
1. Connect the router to the switch with a standard ethernet cable. If an ethernet cable was supplied, don't use it, use a know standard cable.
2. On the switch, from what I can tell, only ports 1-4 support auto MDI. Port 5 does not. You might try plugging the modem into one of those ports.

BTW-
When communicating, be specific, instead of stating "doesn't work", describe WHAT doesn't work. Be sure to check the ethernet port lights....on? off? Color?..etc...this is important for remote diagnostics...

I don't think this issue as anything to do with IP addressing..
eT
 
Last edited:

Yaakov

Joined Jan 27, 2019
2,541
Hint....The PC to Modem connection works. That means the modem (router) is either using a crossover cable, or supports auto MDI.
I didn't see in the modem spec any mention of auto MDI.

So...
1. Connect the router to the switch with a standard ethernet cable. If an ethernet cable was supplied, don't use it, use a know standard cable.
2. On the switch, from what I can tell, only ports 1-4 support auto MDI. Port 5 does not. You might try plugging the modem into one of those ports.

eT
Both components have Auto-MDIX and the problem turns out to be the browser’s treatment of the URL.
 

Yaakov

Joined Jan 27, 2019
2,541
After requesting all of that info from the TS, I had also come to the conclusion that it wasn’t addressing.

Yaakov, I think you’ve got it!
While I don't know exactly what is going on, I think the requirement to use https, along with the way the browser uses DNS, is probably the root of things. The manual offers a way to use the MAC address as a host name by using the built-in dns server in the modem. That will probably make it more reliable. But I think I would be a name in the hosts file because the MAC address is NOT user friendly.

I don't think he needs to use the login part of the URL, just the https:// for it to work the first time. The caching explains subsequent success.
 

eetech00

Joined Jun 8, 2013
2,302
While I don't know exactly what is going on, I think the requirement to use https, along with the way the browser uses DNS, is probably the root of things. The manual offers a way to use the MAC address as a host name by using the built-in dns server in the modem. That will probably make it more reliable. But I think I would be a name in the hosts file because the MAC address is NOT user friendly.

I don't think he needs to use the login part of the URL, just the https:// for it to work the first time. The caching explains subsequent success.
Just a heads up.....nothing I saw in this thread indicates DNS was actually used. The Urls mentioned are all using a host IP to connect.:cool:
All connections have probably been made via ARP/IP mappings.:D
But it does seem that the modem has a clunky interface...:(

eT
 

Thread Starter

xtal_01

Joined May 1, 2016
118
Well maybe I will just check this up to being some kind of "glitch" .... if I just need to use "loging/cgi" the first time I connect to it, I will be OK. With some luck once I set it up, I won't have to go into the modem too many times. I did test everything again.

If I plug the modem in through the switch and type the bare "https://192.168.1.1/" in ... green and orange lights come on (on all devices) but I get the time out error.

Then I type it in with the "login/cgi" it goes to the log in page.

But then, if I yet in the bare "https://192.168.1.1/" it goes to the login page (I don't need the login/cgi).

I tried this a few times. The first time you connect the switch it "needs" the "login/cgi"

Any time after this, I can use the bare "https://192.168.1.1/"

hmmm ... strange

Well thanks for all the help!

I may be asking for more tomorrow ... I will put in the simm card and see what happens ... any words of wisdom before I do this?

I was planning on doing this tonight but we finally had a day here in VT without rain (heck we even had snow here a few days ago) ... the grass was literally 8 inches (it has been too wet to cut it so far). It is going to rain again tonight so I took a stab at cutting it.

Thanks so much again !!!!!!!!

Mike
 

eetech00

Joined Jun 8, 2013
2,302
Well maybe I will just check this up to being some kind of "glitch" .... if I just need to use "loging/cgi" the first time I connect to it, I will be OK. With some luck once I set it up, I won't have to go into the modem too many times. I did test everything again.

If I plug the modem in through the switch and type the bare "https://192.168.1.1/" in ... green and orange lights come on (on all devices) but I get the time out error.

Then I type it in with the "login/cgi" it goes to the log in page.

But then, if I yet in the bare "https://192.168.1.1/" it goes to the login page (I don't need the login/cgi).

I tried this a few times. The first time you connect the switch it "needs" the "login/cgi"

Any time after this, I can use the bare "https://192.168.1.1/"
hi

Apparently there must be an error in the manual. It reads that you can just type "https://192.168.1.1/" but the full login url is needed.
Once you've logged on one time with the full URL, the full URL is cached by the web browser. If you then logon again by typing the short URL, the browser "autocompletes" the URL and appends "login/cgi" to it, after which it successfully connects.

You can test this by "clearing the browser Cache" after a successful logon using the full URL. If you then try to use the short URL, it will probably fail.

eT
 

Thread Starter

xtal_01

Joined May 1, 2016
118
Just odd it only happens with the switch in place ... when you hook it up directly to the computer it works find.

Crossing my fingers this is the biggest problem I have ...

As I said ... learning on the fly.

Thanks ... Mike
 

Thread Starter

xtal_01

Joined May 1, 2016
118
OK .... success ... well almost!

I put the Verizon card into the modem (with the switch in place) ... powered up the modem ... waited a few minutes .... WOW, connection... I am on the Internet!

I did not touch any settings and it worked!

Question, how do I look back from another computer to see mine?

Do I need a program (years ago I had PC Anywhere) ... or ???

I have the Static IP address it was assigned ... I logged into the modem and the address I was given does come up.

If I am on another computer and just type in that address, nothing happens (looks like it is trying to load a page and saying waiting for 51.33.38.230 .. which is not the address I put in or the address I was given).

I am assuming once I get my touch screen and PLC, I will need to set set up some kind of parameters so I can look at them through the modem ???? or is this why the touch screen comes with a program to duplicate the local screen onto a web page?

Thanks again .... Mike
 

djsfantasi

Joined Apr 11, 2010
7,566
OK .... success ... well almost!

I put the Verizon card into the modem (with the switch in place) ... powered up the modem ... waited a few minutes .... WOW, connection... I am on the Internet!

I did not touch any settings and it worked!

Question, how do I look back from another computer to see mine?

Do I need a program (years ago I had PC Anywhere) ... or ???

I have the Static IP address it was assigned ... I logged into the modem and the address I was given does come up.

If I am on another computer and just type in that address, nothing happens (looks like it is trying to load a page and saying waiting for 51.33.38.230 .. which is not the address I put in or the address I was given).

I am assuming once I get my touch screen and PLC, I will need to set set up some kind of parameters so I can look at them through the modem ???? or is this why the touch screen comes with a program to duplicate the local screen onto a web page?

Thanks again .... Mike
What do you mean by “look at back from another computer to mine”? This is important.

Yes, you will need a service or program on the two computers. And some other stuff.

Where is this other computer located? That’s important.

If it’s also connected to the switch and on the same network (I.e. has a 192.168.1.x address), and both machines are Windows, then you need to set up file sharing, define permissions (which could be Everyone). Then File Explorer on the remote machine will let you see and change files on the destination computer.

To run programs on the destination computer initiated by the remote computer, then you’ll need a program like PCAnywhere.

So it depends on what you want to do.

Let’s say you want to access the destination computer across the Internet. There is much more to it.

First, you have firewall services in place. I forget if your modem supplies them. Regardless of anything I discuss here, you need these services. Fortunately, Windows 10 has one built in for the local machine and will protect you from obvious security breaches. But how about your switch?

Then, you need to define routing on your modem. The one static IP address is the only thing you can see across the Internet. To access specific devices, you’ll need NAT and PAT. Which is network address translation and port address translation.

Basically these two services examine an incoming request and translated a public Internet address to a local Internet address. With one public address (the external static address), this service is limited.

The other is port address translation. PCAnywhere uses port 5631. So as to distinguish internal devices, PAT can be used to change the incoming port for security. It is recommended that you use other ports rather than 5631, so that a malicious external site cannot find your internal machine. And since you’ve hooked up to the Internet, I can guarantee you that your network has already been port scanned.

It has been a while since I’ve done this, but the concepts are still valid. The good this is that all of these scenarios have been documented. A search will turn up many step-by-step resources.

But I’ve gone on for way too long. Maybe about stuff you don’t need. So let me take this opportunity to reiterate the important question.

What do you mean by “look at back from another computer to mine”? This is important.
 

Thread Starter

xtal_01

Joined May 1, 2016
118
You gave me exactly the starting point I wanted!

I really just wanted to make sure I could access the cellular modem (and anything connected to it) buy "dialing in" (though since it is a cell modem and not phone I guess it could be called addressing in?).

I just searched the remote desktop function on Windows 10 ... that should work great.

I will connect one of my computers to the cell modem and the other leave connected to the cable modem.

With some luck, I should be able to have the home computer connected to the cable modem talk (access using the remote desktop function) to the one connected to the cell modem.

Thanks!

Mike
 

djsfantasi

Joined Apr 11, 2010
7,566
Sounds like you have a handle on it. And I forgot about the built-in Remote Desktop for Window 10.

Note that the cell modem and cable modem are likely not on the same network. You must ensure that you can establish a connection from one to the other without being blocked by default security and that both networks can see each other.
 

Yaakov

Joined Jan 27, 2019
2,541
Just a heads up.....nothing I saw in this thread indicates DNS was actually used. The Urls mentioned are all using a host IP to connect.:cool:
All connections have probably been made via ARP/IP mappings.:D
But it does seem that the modem has a clunky interface...:(

eT
The fact that there is no DNS available is almost certainly the problem. The browser first tries name resolution and fails. If the URL is specified including the scheme, and possibly also the trailing /, I expect it will work on the first try without the path, since the redirection to the login.cgi path after the first get is made by the https, not the browser.
 

eetech00

Joined Jun 8, 2013
2,302
The fact that there is no DNS available is almost certainly the problem. The browser first tries name resolution and fails. If the URL is specified including the scheme, and possibly also the trailing /, I expect it will work on the first try without the path, since the redirection to the login.cgi path after the first get is made by the https, not the browser.
Hi

DNS is only used for resolving the “Host Name” portion of the URL. The host name can be a “single label name” or FQDN. Since an IP address is specified in the URL, DNS is never used.
This is perfectly OK. The Browser really doesn’t care but will make a low level call to DNS if an IP is not specified. DNS is only used for resolving friendly names (single label or FQDN) to IP addresses.

eT
 

Yaakov

Joined Jan 27, 2019
2,541
Hi

DNS is only used for resolving the “Host Name” portion of the URL. The host name can be a “single label name” or FQDN. Since an IP address is specified in the URL, DNS is never used.
This is perfectly OK. The Browser really doesn’t care but will make a low level call to DNS if an IP is not specified. DNS is only used for resolving friendly names (single label or FQDN) to IP addresses.

eT
The browser has to recognize whether what is typed in is a host name or an address in dotted decimal notation. Some browsers, when faced with an incomplete URL (e.g.: lacking the scheme part) will attempt to use DNS to resolve it as if it were a host name. If this fails, you can find yourself on a search page (if you have a connection to the Internet) or with an error if not.

If the complete, or a sufficiently complete, URL is used, the browser will use the hostname part as an address from the outset and not run into this problem.

The behavior he describes where the switch seems to interfere with this initial connection, if it is repeatable, could have to do with routing. With the direct connection, all traffic on the wire will be visible since there is a single collision domain. With the switch, some traffic might fail to get to the port the computer is plugged into since the switch will only send unicast and explicit broadcast traffic to that port.

Once the address is recognized, the routing table is consulted by the IP stack. If there is a route to the host (because it was heard on the interface already), then the traffic can be routed. If not, it will have to use the generic routes listed. In this case, the 192.168.1.1/255.255.255.0 and so will ARP to get MAC address since the specified address is in its own network and the route is via its own interface. But, this is only true if the dotted decimal notation is recognized by the browser as an IP address and not a hostname. If there is a scheme preceding the address, it will, if not, it may try to resolve the address and the resolved will return an NXDOMAIN result causing the browser to fail.

So, DNS is relevant here if the browser tries to use it, and I have seen browsers do just this. In particular, a bare "192.168.1.1" in a browser will return a search page (Google, etc.) with it as a search term while "https://192.168.1.1/" will work as expected.

Hence my suggestion of populating the host file with some friendly name to make it consistent and easier. That way, when the resolver does its thing, it will first check hosts and get a hit, no resulting confusion.
 

Thread Starter

xtal_01

Joined May 1, 2016
118
My wife says I should just throw a big party and invite all you guys to move in for a week ... the knowledge you have is amazing!

Two things ...

1) I choose a switch just because I always do for my home network. I was told long ago it is more efficient at handling data as it chooses the correct port to send the data. Since I only have three items and speed is not an issue (really the PLC and touch panel will almost always be the only two things talking to each other .. as I said, the plc will only send on e-mail a day and I would be surprised it they log in once a week to turn on a pump which will take only a few seconds) should I have chosen a hub instead? My understanding is that a hub takes data in on one port then re-broadcasts it to all ports with no changes. I just did a quick check and don't even see one listed on any sites ... they all say "hub" but then go on to say "switch" ... but they must be available.

2) Hit a dumb road block last night ... the modem manufacturer sent a "critical update" notice ... said the modem will stop working at the end of the month if not installed. So I tried to install it. Seemed to go OK till the last step and then getting a "failure to connect" message.

I did a bit of searching around on in the modem set-up. I have it down to two possible problems ... a) it just screwed up during the flash update b) the SIMM card they sent me has not "time" (well I guess I should call it data) left on it. I was told it was 5 Gig per month but I see in the settings I used 40,000 Kb and it says 0% left ... but this could also be because it is not recongizing the card.

The modem manufacturer and Verizon business department are both closed today. I will get a call into both tomorrow and see what is happening.

If I can get the modem up and running, I want to get the PLC and Touch panel on order this week ... both in stock ... free two day delivery. By next weekend I might be begging for your help in setting them up with the modem.

You guys don't know how very much I appreciate the time you have all taken to help me with this!

Thanks again ..... Mike
 

Yaakov

Joined Jan 27, 2019
2,541
I expect you will get the update installed.

When you are done with that stuff, check out the idea of using the Windows hosts file to give things friendly names. It's just an easily edited text file which will make your URLs easier, like "https://modem.local/' or any other device. The ".local" TLD (Top Level Domain) is the one used by mDNS (Multicast DNS) so it will be compatible with things that use it.

Good luck.
 

eetech00

Joined Jun 8, 2013
2,302
The browser has to recognize whether what is typed in is a host name or an address in dotted decimal notation. Some browsers, when faced with an incomplete URL (e.g.: lacking the scheme part) will attempt to use DNS to resolve it as if it were a host name. If this fails, you can find yourself on a search page (if you have a connection to the Internet) or with an error if not.
If an IP address is used in the hostname of the URL, the browser WILL NOT use DNS. And yes...it will attempt to use DNS if a name is used, even if it is an incorrect name(as in an incorrectly formatted name).

If the complete, or a sufficiently complete, URL is used, the browser will use the hostname part as an address from the outset and not run into this problem.
Whether it runs into a problem or not depends on the target URL...

The behavior he describes where the switch seems to interfere with this initial connection, if it is repeatable, could have to do with routing. With the direct connection, all traffic on the wire will be visible since there is a single collision domain. With the switch, some traffic might fail to get to the port the computer is plugged into since the switch will only send unicast and explicit broadcast traffic to that port.
I agree that the switch might be having issues. But don't agree with your description.
When a layer 2 switch boots up, it will immediately flood all ports with ANY traffic received on ANY port until it "learns" the source MAC being received on its ports. It will then use that information to populate its forwarding table and begin to forward unicast traffic to specific ports. Broadcast traffic is ALWAYS forwarded to ALL ports.
Of course, this is basic layer 2 switch behavior but on some more advanced switches this behavior can be manually changed.

Once the address is recognized, the routing table is consulted by the IP stack. If there is a route to the host (because it was heard on the interface already), then the traffic can be routed. If not, it will have to use the generic routes listed. In this case, the 192.168.1.1/255.255.255.0 and so will ARP to get MAC address since the specified address is in its own network and the route is via its own interface. But, this is only true if the dotted decimal notation is recognized by the browser as an IP address and not a hostname. If there is a scheme preceding the address, it will, if not, it may try to resolve the address and the resolved will return an NXDOMAIN result causing the browser to fail.
Sorry...but I can't make sense of what is being described here..

So, DNS is relevant here if the browser tries to use it, and I have seen browsers do just this. In particular, a bare "192.168.1.1" in a browser will return a search page (Google, etc.) with it as a search term while "https://192.168.1.1/" will work as expected.
:rolleyes:
There's nothing in the user manual that says you should be able to access the management page using a DNS name. I think your stuck on DNS when a simpler troubleshooting approach might help.

First, just try "ping" between each of the directly connected devices to be sure they can communicate.
(this doesn't require routing to work).
Then, use "tracert" to check routing. You can use this from the PC to see if routing thru the modem is configured.
Lastly, use "nslookup" at the PC to see if Name Resolution is working.

Hence my suggestion of populating the host file with some friendly name to make it consistent and easier. That way, when the resolver does its thing, it will first check hosts and get a hit, no resulting confusion.
Yes...that could help.

eT
 
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