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TZ300/350 Unable to get DHCP from Comcast cable modem

Home internet went out this morning, after rebooting the cable modem multiple times, and a fruitless call with Comcast support, I checked my TZ300, X1 is configured for DHCP. It showed as the WAN address. I moved the cable to my TZ350, which also showed as the WAN address. Hit the renew button, refreshed the page, rebooted the sonicwall, rebooted the cable modem again... no change.

Plugged the cable into my computer, and I got an address instantly. Plugged back into both of the Sonicwalls and nothing. There have been no configuration changes or OS updates on the Sonicwalls, I can see DHCP discovers in the pcap, but the sonicwall doesn't get an address.

The cable modem is configured in bridge mode, and has been for years, so I can have a routeable address on the firewall, and I've never had a problem like this before.

It doesn't make sense that the computer gets an address without issue, but 2 different sonicwalls can't get DHCP from the cable mode.

I realize I can change the cable modem so it's doing NAT, and assign the firewall a static IP address, and that's fine for a work-around, but I'd like to get it working the way it's supposed to.

Any ideas?

Category: Entry Level Firewalls


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    shultisshultis Newbie ✭

    Update: Tried a different brand of firewall and it's not getting DHCP either.

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    SliderhomeSliderhome Enthusiast ✭✭
    edited June 2022


    On the Computer first do a DHCP Release, after that you can move the cable over to the TZ350.

    ipconfig /release

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    JimmywickJimmywick Newbie ✭

    Cable providers usually save a client's MAC address for a specific time, preventing other people from accessing the Internet. Power cycling your modem may help.


    J Wick

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