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?