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Odd Networking Issue

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Advanced Tutor

Odd Networking Issue

I'm posting this for all the Network Geeks here. Also, because I would have mis diagnosed this issue if it had been posted here by a customer.

We ran into an unusual problem with one of our customer's Gen4 systems we installed about a year ago.

It's in a retail environment with a wireless router, two Point Of Sale terminals and PC controlling the POS terminals, an Internet-connected audio streaming box, a video surveillance DVR with four cameras, and a HughesNet Voice ATA. 

Recently, the modem started to go completely off line, first losing TX lock, then RX lock, then System lock. Before this, the customer reported having to reboot the modem every week or two to restore functionality to the POS terminals. This had been going on for several months and they had just been living with the problem. 

From the description, I had assumed we were looking at a simple modem or radio failure. When I arrived, the modem was off line, with only the POWER and LAN lights lit. But as soon as I bypassed the all the customer's gear and connected my laptop directly to the modem, the modem's TX, RX and System lights came back on. It was at this point that I started tracing out the local network architecture.

Someone had connected all of the customer's devices to the HughesNet modem's LAN jack through a couple of cascaded 8-port network switches. (I think it may have been the surveillance Tech attempting to establish remote access to the camera DVR). 

I would not have thought that simply overloading a Gen4 modem's LAN side with too many devices would actually cause the modem itself to go off line. I would have thought this would simply create some local network conflicts, and "orphans," with too many devices competing for the modem's limited internal DHCP pool of only five IP addresses.

I rewired the customer's network to connect only one of the switches to the modem's LAN jack and then connected the two POS terminals and controller PC, and the wireless router's WAN port to the switch, I then connected the rest of the gear to the router's LAN ports, with the cameras and DVR connected to the router through the second 8-port switch. This apparently solved the problems and the customer reports all is well. 

It may well be that the camera DVR had it's own DHCP server running, creating further network conflicts, but I didn't have the time to troubleshoot that further.

I mention all this because it may well be that a few apparent modem problems could simply be due to a customer's mis-configured or overloaded local network. Typically, most customers don't have such an assortment of gear, and most have a router first in line, so this wouldn't come up very often.
"Experience" is something you don't get until just after you need it. - Steven Wright
El Dorado Networks |Diamond Springs, CA | eldoradonetworks.com
4 REPLIES 4
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Honorary Alumnus

Re: Odd Networking Issue

Interesting.

I do question why a subscriber that had need to connect multiple devices why rely on the Hughes moden to handle DHCP duties when a router would provide more robust service.
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Assistant Professor

Re: Odd Networking Issue

From your description I'm surprised anything was working right. Probably all kinds of addressing conflicts going on. Am also surprised it shut the modem down like that.

Thanks Alan, go info to know. Once again proves the case that have to be able to connect one computer directly to the modem for troubleshooting purposes.
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Advanced Tutor

Re: Odd Networking Issue

I do question why a subscriber that had need to connect multiple devices why rely on the Hughes moden to handle DHCP duties when a router would provide more robust service.
In this case, the HughesNet customer was not responsible. It may be that one or more of the vendors (POS, Security, Audio) who connected their gear after we installed did not know that a HughesNet modem would only serve up a maximum of five IP addresses.

I suspect the security guy since he was the last to touch it. Customer said he was trying to establish remote camera access, and may have totally rewired the network trying to make it work.
El Dorado Networks |Diamond Springs, CA | eldoradonetworks.com
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Alum

Re: Odd Networking Issue

Hi Alan,

Yes that is very interesting. Don't even know how they had it working either. Seems like a one off situation. But it makes sense. Good thing you had the know how :-). Thanks for sharing. 

- Chris