CM1200 does not assign IP address unless Ethernet cable is unplugged and plugged back in

[zbrozek]

I bought a CM1200 yesterday to replace a super-flaky SB8200. Unfortunately, the CM1200 only allows me to get an IP address right after cycling the Ethernet cable. This is a problem, as whenever I change settings my router reboots itself and I have to go cycling a cable to reestablish connectivity. There are no settings to speak of in the device configuration, so I can only assume that this is a firmware bug.

[FURRYe38]

Swap the LAN cable between the modem and your connected device. CAT 6 is recommended. 

What device do you have connected to the modem? PC or External router? Mfr and model#?

[zbrozek]

Same problem reproduces with six different cables, including the brand-new one that shipped with the CM1200.

[FURRYe38]

What device do you have connected to the modem? PC or External router? Mfr and model#?

[zbrozek]

I've tried two devices. One is plan-of-record, the other is for debugging.

Debugging device is an ancient WRT54G. Plan-of-record device is a computer with an Intel NIC attached to a VM running pfsense. Right now whenever I change a setting on the WRT54G, it reboots itself. With the VM, if I ever reboot it, the NIC doesn't actually bring down the PHY - it just asks for a new IP on restart.

It doesn't seem like there should be any connection between responding to a DHCP request and link history.

[FURRYe38]

Any chance you have a more up to date router? Something to test with to see if the CM still hands out and IP with out having to unplug and plug in the LAN cable? 

I didn't see this issue with my 1200...

[zbrozek]

The VM is about as up-to-date as it gets. That said, I see the same behavior with my Thinkpad. If I unplug the cable and replug it in, the next dhcp client request works fine.

I'll try to collect more data, including some tcpdump logs.

[FURRYe38]

Might contact NG support and send them your logs.

@vkdelta 

[DarrenM]

Yes I suggest contacting support and if you have any issues getting ahold of support to send me a PM.

https://www.netgear.com/support/contact.aspx

DarrenM

[vkdelta]

Almost every ISP has max_CPE set in the DOCSIS Config file to value of just "1".

that means only 1 IP goes out to the CPE behind modem.

Now, when you have a CPE with MAC address aa:bb:cc:11:11:11 attached to the device and has got an IP, only this MAC will be allowed to get an IP unless you wait for a while (I forgot exactly how long) or power cycle the modem.

can you please capture bootp?

Have you seen this issue on SB8200?