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DHCP negotiation failure

I'm having a problem with intermittent connectivity to my ISP.  Every few minutes, hours, or days (it varies) my internet connectivity will slow to a crawl and eventually fail altogether.  No traffic in or out.  The solution is to reboot the firewall and then service will return until the next incident.  The components involved are a Watchguard SOHO 6 firewall to a Motorola Surfboard 5120 cable modem to the ISP, Suscom.   The Soho is at the latest firmware revision.
The Soho's log file reveals that DHCP negotiation may be part of the problem.  I'm seeing a recurrence of the error message "DHCP response has incorrect ID" timed coincident to the slowdown of internet connectivity.  Otherwise the log file looks normal.   In an attempt to resolve the issue I have installed a hub between the Soho and the cable modem but that has not helped.  I've also tried stepping down the Soho's WAN link speed to 10 half which has not improved things.   Suscom support is unable to find any problem with their service.  Suscom and Watchguard both claim their equipment to be RFC compliant.   My options, as I see them are to swap the Soho or to swap ISPs or to pull more of my hair out (which I really can't afford.)

So, my collegues, the question is:  What tools or techniques might I employ to further diagnose the source of this apparant DHCP problem?
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pnkljohnson2
Asked:
pnkljohnson2
2 Solutions
 
skags442Commented:
for testing's sake, take the soho out of the picture and see how you pc deals with the connection, if all is good with the pc, then you can safly assum its the soho, and if thats the case, your isp might have a certin thing that may need to be set, like the mtu settings. but i would first make sure its the soho first.
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skags442Commented:
another thing you could try is dissconnect your cable modem from everything including the coax, and let it sit for about 5 min, and try it again
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ded9Commented:
http://www.gfi.com/

download tools from the above site detects any kind of network problems

Its the no1 software in the market

Reps
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wtbservicesCommented:
You said that restarting the router clears the problem so that is where I would start looking. Since you have a hub in the line between the modem and the router I would connect a computer  into the hub and run Ethereal to capture the traffic. Then initiate a DHCP renew on the router and see if you can observe the 4 DHCP packets back and forth (discover, offer, request, acknowledge). Bear in mind that this would likely only be usefull once the connection is down although it could be informative to see what was happenning when it was running smoothly. Also, be sure that the computer you have connected to the hub has a static IP address assigned since you don't want it sending a DHCP request to the modem.
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monkeyjrCommented:
Please check the DHCP request is from which device by its MAC address. Also check the firewall setting, it seems the DHCP service become DoS attack. Or you can try to drop those packets when these packets come to the firewall from same machine in a short period (ping request, DHCP request, etc).
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pnkljohnson2Author Commented:
Sorry for not getting back.  I haven't yet returned to the customer's site.
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