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Linux Server Question


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#1
craeft

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Hey all. I was wondering if you could help us out a bit.

Currently, we are running a Linux server to a 56K modem (ugh) to get out on the wire, and internally, all boxes have WIN2K installed. We're running the internal network to the Linux gateway and if there is any load on the bandwidth, it drops us and redials. This is excellent if the modem dumps, but often times, minimal bandwidth usage will drop us. We WERE running WIN2K on ICS and we didn't dump near this bad, but we also had to deal with mass amounts of trojans and other fun 'gifts' due to Windows' incredible security *cough*.

Basically, the way we have it set up is that the Linux box will send out a ping every 30 seconds. If a number of those pings don't return to the box, it will dump the modem and redial. The purpose of this is because we were having a problem where the modem would stop transferring data, but wouldn't disconnect. This forces a disconnect/reconnect in those situations. My THEORY on what's happening is that if someone is loading a page and it sends out that ping request, and for whatever reason, the ping is snuffed out due to the already used bandwidth, and even though the packets are getting through, the Linux box sees it as a dead modem and dumps.

So my question is this... has anyone else had this problem or know how to rectify it while maintaining the safety net of modem redial?
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#2
Kemasa

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Have you tried a different make of modem? You might also look at the flow control that you have on the modem. If you have both hardware and software, it might be that the software flow control is getting messed up and causing the modem to stop.

Depending on where you are located, you might want to check out DSL since that can be cheaper than dialup service.

You could also modify the control to dump the modem and instead of just dumping the modem and restarting, check to see if anything is returned and also check the traffic. Sometimes it can take some time to get a response to the ping when there is a lot of traffic, so that is not 100%, as you have seen.
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#3
craeft

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Have you tried a different make of modem? You might also look at the flow control that you have on the modem. If you have both hardware and software, it might be that the software flow control is getting messed up and causing the modem to stop.

Depending on where you are located, you might want to check out DSL since that can be cheaper than dialup service.

You could also modify the control to dump the modem and instead of just dumping the modem and restarting, check to see if anything is returned and also check the traffic. Sometimes it can take some time to get a response to the ping when there is a lot of traffic, so that is not 100%, as you have seen.



My partner in crime has tweaked the flow controls and has been playing with that for the past couple weeks. We had a mild improvement (very mild... took about 15 minutes instead of 10 to dump the modem) and then right back to where we are now.

We actually need the modem to redial upon dump since the server is in another building. He has been monitoring the traffic and is just as stumped as I am on what's going on (a little background, he was network admin for the government for about 15-20 years). The fact that it may take some time to get the ping return is expected. The problem is that it times out completely. I have a network monitor sitting on this computer, pointed at the server, and I have Command Prompt open pinging 4.2.2.2 continuous just to monitor our connection to the outside world and what's happening is it's pinging and 'request timeout' until modem redial.

As for where we live, we live so far out in the middle of no where that we can't even get satellite. Cable, DSL, Satellite, Terrestrial RF, and Cell Tower ISP are none available. *sigh* Ahhh.. great land of rural michigan. We even contacted Wild Blue (Satellite service that is supposedly available ANYWHERE) and they're not installing in this area and have no intention to. We're trying to get an investor so that we can set up a 900 MHz terrestrial RF ISP here (we've done it before and it works better than any high speed I have ever used). But that's going slow. Few investors (none in the area) know enough about ISPs and the Internet overall to want to jump onboard, although we already have a client base available for immediate ROI. But anyway... that's another topic entirely.
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#4
Kemasa

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Have you tried another modem? It might help or make no difference, but until you try you don't know. Sometimes there can be issues with some makes and compatibility with other modems. You could contact your ISP and see what modems they use.

I have seen a similar thing with my modem (can't get DSL here and the cable company lied to me too many times). It is not all that much of an issue with me though. I suspect to find out what is going on you would need to look at the connection with respect to the phone line and what the modem thinks is going on, which is difficult to do.

How are you doing the ping?

You might consider something like: ping -c 1 -W 1 MACHINE, so that there is only one packet sent and the maximum timeout is 1 second. You can then determine what to do quicker. The ping will timeout completely when the connection is no longer working, which is really what the problem is. My router tends to reconnect within a minute or two on its own (SMC 7004ABR, which has a serial port to connect to a modem).
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#5
craeft

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Have you tried another modem? It might help or make no difference, but until you try you don't know. Sometimes there can be issues with some makes and compatibility with other modems. You could contact your ISP and see what modems they use.


We haven't tried another model. Worth a shot. We have 2 robotics v.92s, but they're both the same model.

I have seen a similar thing with my modem (can't get DSL here and the cable company lied to me too many times). It is not all that much of an issue with me though. I suspect to find out what is going on you would need to look at the connection with respect to the phone line and what the modem thinks is going on, which is difficult to do.


There's actually the possibility that it's the physical lines themselves, but I don't buy it completely because everything was working fine when we were using WIN2K with ICS for the connection. It was when we switched to the Linux box that it started getting really bad. When we had the Windows plat. as the connection server, it would dump, but not NEARLY as often... maybe 3 or 4 times a night as opposed to the current 3 or 4 times in a half hour (that's giving the benefit of the doubt).

How are you doing the ping?


Command Prompt to get below the application layer. :

ping -t 4.2.2.2

You might consider something like: ping -c 1 -W 1 MACHINE, so that there is only one packet sent and the maximum timeout is 1 second. You can then determine what to do quicker. The ping will timeout completely when the connection is no longer working, which is really what the problem is. My router tends to reconnect within a minute or two on its own (SMC 7004ABR, which has a serial port to connect to a modem).


I'm not familiar with that command. What's it do exactly? Is MACHINE a variable?

Thank you for your attention to this thread, by the way. This has been driving me nuts.


EDIT: I tried the command and it gave me the ping help list. After reviewing the list, I altered the -c to -n and am still getting the help list.

Edited by craeft, 05 April 2006 - 05:12 PM.

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#6
Kemasa

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Where you using the same modem with Windoze?

I am using a USRobotics too with similar issues, but not as bad. I should try the other modem I have, but I have not set it up yet. It could be something with the modem. If you watch the modem it keeps trying to send data, but gets nothing back, until it drops out and redials.

The ping command I sent is just different options, "-c 1" to send one packet, "-W 1" to wait one second before timing out. MACHINE is just the machine you want to ping. The options may vary depending on the machine that you are on. Are you running the ping from the Linux box? What is the help from your ping command?

I would not think that it is the phone line either, except perhaps in how the modem is dealing with it, assuming that you are using another modem than before. If it is the same modem, then either something changed or there is something else causing it.
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#7
craeft

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Where you using the same modem with Windoze?


Yeah. Same modem.

I am using a USRobotics too with similar issues, but not as bad. I should try the other modem I have, but I have not set it up yet. It could be something with the modem. If you watch the modem it keeps trying to send data, but gets nothing back, until it drops out and redials.


Yeah. Pretty much... except if the modem is left stand alone, it doesn't redial. It sits there pretending to be working, which is why we had to force redial.

The ping command I sent is just different options, "-c 1" to send one packet, "-W 1" to wait one second before timing out. MACHINE is just the machine you want to ping. The options may vary depending on the machine that you are on. Are you running the ping from the Linux box? What is the help from your ping command?


Running the monitor ping through the Linux box from a windows box. Running the redial ping from the Linux box.

I would not think that it is the phone line either, except perhaps in how the modem is dealing with it, assuming that you are using another modem than before. If it is the same modem, then either something changed or there is something else causing it.


I don't think anything was changed. We entertained the idea of it being the ISP's modem pool failing, but I don't buy it. It happens no matter which pool we connect through.
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#8
Kemasa

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I am not sure of what to say other than to try another modem (which I also need to do). I am not sure of why the Windoze box would not have a problem when the Linux box does. In my case, it is using a router so that Linux does not play a role. It may be something in the modem settings. I have gone through the settings and did not see anything obvious.

One thing that you could try is to connect the modem to a Windoze box, get it to dial and then connect to the modem and save the settings. It may be that Windoze is changing a setting which bypasses the problem. I know it changes settings when it dials, but I don't know what. Attaching a terminal to the serial line would show what it is changing (just the transmit of the Windoze box to monitor what it sends).

If you do that I would be interested in knowing what you find.
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