on 23-11-2021 14:52
Hi All,
For some reason I can no-longer get a DHCP address when my hub3 is in modem mode. It was working for months up until a couple of days. Virgin support don't really seem geared up to support modem mode and said they would escalate and email me (nothing received as yet). I have a Cisco router connected to port on of the hub and according to debug I can see the Cisco requesting a DHCP address, but nothing is coming back. I've rebooted everything and also changed the cable between the router and the hub. I suspect a problem with the upstream DHCP server, but have no way of finding someone who can check it for me.
Any ideas? Thanks, Simon
Answered! Go to Answer
23-11-2021 20:14 - edited 23-11-2021 20:16
If that works copy the MAC to your Cisco router and see if that works if not on your laptop that work go to Registry Editor
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\key that gets the WAN IP
set
DhcpConnForceBroadcastFlag to 1 and reboot to test DHCP by Broadcast should your Cisco router do DHCP by Broadcast and not by Unicast
on 23-11-2021 14:58
It needs to be done is a certain order, as the Hub will hang on to MAC addresses at times.
Set Hub to Modem mode and confirm. Once done switch it off
Power up your Router in DHCP mode and leave it switched on.
Connect the Router's WAN port to the Hubs LAN using as known good Cat 6 cable. Only one port is active in Modem mode, so there should be no other ethernet cables attached.
Power on the Hub and wait for it to stabilise.
You should be good to go. This only needs done the first time you attach a new Router. Once the new Router MAC is stored it will work with any power on sequence.
I'm a Very Insightful Person, I'm here to share knowledge, I don't work for Virgin Media. Learn more
Have I helped? Click Mark as Helpful Answer or use Kudos to say thanks
on 23-11-2021 15:17
23-11-2021 17:26 - edited 23-11-2021 17:27
Excellent idea, but be sure to power off hub before connecting the PC and power it on when the PC is up and running.
23-11-2021 20:14 - edited 23-11-2021 20:16
If that works copy the MAC to your Cisco router and see if that works if not on your laptop that work go to Registry Editor
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\key that gets the WAN IP
set
DhcpConnForceBroadcastFlag to 1 and reboot to test DHCP by Broadcast should your Cisco router do DHCP by Broadcast and not by Unicast
on 23-11-2021 21:00
Laptop works fine. If I switch the hub3 to routed mode, the cisco router is able to pick up a DHCP address from the hub (albeit a private IP). Think this proves the cable and the Cisco router are fine, especially given it was working for months up until a few days ago. I've even tried defaulting the hub. Still no joy. Fairly convinced my the cisco MAC address is not playing ball with the upstream DHCP server. Unfortunately, I can't change the MAC address on the cisco as it's not supported on this model (897). I have an cisco ASA lying around that I will try in the next day or so.
Cheers, Simon
on 23-11-2021 21:46
on 23-11-2021 21:48
on 23-11-2021 22:26
The VM CMTS only keeps one MAC address for your service. If you change to a different MAC address without the VM hub being the last device powered on you will never get a new DHCP lease. I have changed my router numerous times and EVERY time I have had to fully initialise my router with the VM hub switched off and then power on the VM hub. I have never had any trouble following the correct sequence. You can ‘fudge’ it by copying MAC addresses, but that’s not good network etiquette.
on 23-11-2021 22:34