How does theWAN IP address get assigned on virgin media broadband ?
 

Hi

I am currently using virgin media broadband, have put the modem (Hub 3.0) into modem mode and hooked up a wireless router (currently a Belkin).

All this has been working fine for a while, but I'd like to change the router I am using and when I do so I do not get assigned a WAN address.

I have not had a chance to dig deeply in to this, but I am trying to work out what has to happen to get the address assigned.

I assume the router sends a dhcp request out of the WAN interface to the ISP dhcp server which eventually responds with a leased WAN address for the router.

Is that correct ? Or does the modem itself somehow get involved (till now I've been assuming that in modem mode all layer three comms comes from the router and simply gets forwarded to the coax interface, but I guess that could be an invalid assumption).

I'm trying to work out:

how the ISP server to send the request to is specified, or if it needs to be specified at all (router config, modem config ?)

if the dhcp server address does not need to be specified how does the virgin media dhcp server know the request is for it (and conversely other dhcp servers know to ignore it) ?

how virgin identifies me as a user - does it use the mac address of the router, mac address of modem or something else entirely ?

and how do I configure things such that the correct 'userId' is included in the dhcp request ?


Does anyone know where I can find an overview (sequence diagram ?) of how the wan ip address is assigned to the router for virgin broadband ?

Re: How does wan ip address get assigned to the router on virgin me dia broadband ?
 

Your problem is that you've not rebooted the Hub since plugging in your new router. This is a common problem and used to happen a lot more often with standalone modems.

However, for more information, your IP is leased to the MAC address of the device you plug into the hub (In modem mode only - when you put the hub in router mode, it gets assigned the WAN IP via its own interface). If you plug in a device with a different MAC, it won't assign a second one without a reboot.

Sometimes a reboot isn't enough and you have to flush the cache. It's been a while since I did this so I don't know if it'll work on the hub, but it always fixed the issue with the old standalone modems:

1. Power off the hub
2. Connect your new device into the hub
3. Unscrew the Coax cable
4. Power on the Hub (With coax removed)
5. Leave for 2 mins (no less)
6. Screw coax back in (Do not power off the hub while you do this)
7. Leave for another 2 mins

You should get assigned a new WAN IP. If this still doesn't work, power cycle one more time, rebooting the hub first, then leaving it a minute before powering on the router.

Alternatively if you know the MAC address of your old router, you can usually change the MAC address on the new one to get your old IP back.

Re: How does theWAN IP address get assigned on virgin media broadband ?
 

Thank you very much for the reply.

No I haven't tried plugging in the new router then rebooting then rebooting the modem! I will give this a go when I get the chance (quite hard to get a good time since it of course breaks the internet for everyone).

> your IP is leased to the MAC address of the device you plug into the hub
Ok, so rebooting the modem should give me a new lease paired with the mac address of my new router (I'm not worried about the change in wan ip address so I won't try to pretend it's the old device).

Still a bit confused about how the dhcpserver knows the request is coming from me - do you know what it is that identifies me as a virgin media account holder, so it knows that it should assign an ip address at all ? Or is that identification done at a different stage ?

Re: How does theWAN IP address get assigned on virgin media broadband ?
 

That's done at a different stage, that's to do with the modem/hub itself and how it's provisioned. I believe it's part of DOCSIS - The Hub is essentially loaded with crypto keys that identify you as a subscriber, which the CMTS can use to check if it should grant you access or not. You can take your hub and plug it into a different house and it'll work for that very reason.

People used to steal internet by cloning the MAC address of the standalone modems, but that has long since been stopped thanks to extra security put in place by DOCSIS3.

Re: How does theWAN IP address get assigned on virgin media broadband ?
 

Thank you very much for information regarding client identification mechanism.
Have not yet had a chance to re-try the new router connection.

Re: How does theWAN IP address get assigned on virgin media broadband ?
 

For closure - I successfully configured and hooked up my new router over the weekend.

Thank you very much for you help

Re: How does theWAN IP address get assigned on virgin media broadband ?
 

Glad you got it sorted!