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DHCP in modem mode

si-the-pie
Tuning in

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

12 REPLIES 12

Sorry, I have a beginners Q with respect to modem mode.

1. When you enable modem mode of the VM hub, I have read that only 1 ethernet port is left enabled.  Is it any (and only) 1 of the 4 ethernet ports on the hub, or is it a specific ethernet port that is enabled?

2. I assume when I use a 3rd party wifi router, this new wifi router will become the DHCP server for all IP addresses in my home network?  (i.e. the vm hub dhcp server service is automatically stopped in modem mode?)

3. I assume the the VM hub becomes a DHCP client to the Wifi Routers DHCP Server service and that internal IP address of the VM hub (the IP address of the single ethernet port) is assigned from the routers DHCP service?   OR, does the VM Hub just assign itself a specific static IP address? If so, what address is assigned?

4. I see there are plenty of references in the community to putting the VM hub in modem mode, powering it off, powering on the 3rd party wifi router, configuring it, then connecting the VM hub to the wifi router via ethernet and powering it on.  Are these steps documented anywhere?

Thanks for any pointers... JD

Can’t thank you enough. No other tutorial spoke about the importance of the order or said to power down and wait etc. I’m now learning those were VERY important steps. Massive thanks 

Tudor
Very Insightful Person
Very Insightful Person

1) any port

2) yes

3) your router becomes a DHCP client to the VM CMTS, the hub is not involved. Your router is also a DHCP server for your LAN.

4) not documented by VM, full instructions below:

How to put a VM hub into modem mode:

1) Access your hub on 192.168.0.1, sign on and put it into modem mode. On the Hub3 the bottom LED will change to magenta, on a Hub4 the LED band will be green. Best done from a wired connection.

2) Turn off the hub and disconnect any Ethernet cables

3) Fully initialise your own router or mesh master unit and make sure the WAN port is set to DHCP

4) Connect your router or mesh master unit to the VM hub with an Ethernet cable, Cat5e or Cat6, any higher specification is a waste of money

5) Turn on the VM hub.

6) You should now be able to access the internet and the hub will now be on 192.168.100.1

Note1: this only needs doing once for each new router or VM changes your WAN IP address.

Note2: If you have a Hub4 and your own router is NOT 192.168.0.1 then it’s possible that you can still access the VM hub on 192.168.0.1


Tudor
There are 10 types of people: those who understand binary and those who don't and F people out of 10 who do not understand hexadecimal c1a2a285948293859940d9a49385a2