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Standard User Daemon66
(newbie) Wed 13-Jun-12 13:38:19
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Modem Mode Network


[link to this post]
 
Do Virgin put you onto a separate network if you activate Modem Mode?

I'm not having any issues but I did notice something odd when I recently had my old 20Mb connection upgraded to 100Mb. Obviously I had the old modem swapped for a Superhub which the installer left in normal mode.

When I checked my public IP it had, not surprisingly, changed. I was expecting it too since a different device was now connecting to the VM network. However, on switching the Superhub into Modem mode I got my old public IP back!

Obviously I don't care what my public IP actually is (that's what DynDNS is for) but I was surprised at this behaviour. Can anyone explain it? My guess is that Virgin want those who use Modem mode to be on a separate network segment, but I have no idea why that may be.
Standard User JonasTone
(learned) Wed 13-Jun-12 13:54:41
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Re: Modem Mode Network


[re: Daemon66] [link to this post]
 
Im not sure, but im on VM 100Mbit and still using the VMG300 modem even tho EVERY time i call them, they tell me that it cant get 100Mbits, even though i have speed tested and received 106.9 Mbits peak, and double speed(up to 120 mbits) isn't even active yet

I hate the way my IP has change while i was away on holiday, since i have been back the connection has been less than its usual self and all because the IP address has changed
Standard User jchamier
(knowledge is power) Wed 13-Jun-12 18:23:52
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Re: Modem Mode Network


[re: Daemon66] [link to this post]
 
In reply to a post by Daemon66:
Can anyone explain it?


Yes, if you're using the same older router that you used with the old cable modem.

Its the hardware address (MAC address) of the router that is being passed to Virgin's DHCP server, and that looks up in its list, finds its given you an IP before, and returns the same one.

You're lucky the area you're in there are plenty of spare IP addresses, so yours wasn't re-used in that time.

James - be* pro - 16.8 or 17.2mbps BQM
No FTTC cabinet yet (due Mar 2011) at THFB PCP 5


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Standard User kwikbreaks
(eat-sleep-adslguide) Wed 13-Jun-12 19:23:14
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Re: Modem Mode Network


[re: jchamier] [link to this post]
 
Yes as that's the way it works I really can't believe that the SH got the same IP as the modem it replaced. I imagine it was just a similar IP - I've had mine change once in the past but didn't spot it had until I noticed my TBB monitor had stopped working - the last bit was unchanged ie n.n.n.17 became m.m.m.17 and maybe some of the n/m were the same too.

The old modem probably wasn't on DOCSIS3 but the Superhub will be. The change in performance probably only demonstrates different congestion levels between the old and new networks locally.
Standard User Ignitionnet
(knowledge is power) Thu 14-Jun-12 09:35:07
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Re: Modem Mode Network


[re: kwikbreaks] [link to this post]
 
In reply to a post by kwikbreaks:
Yes as that's the way it works I really can't believe that the SH got the same IP as the modem it replaced. I imagine it was just a similar IP - I've had mine change once in the past but didn't spot it had until I noticed my TBB monitor had stopped working - the last bit was unchanged ie n.n.n.17 became m.m.m.17 and maybe some of the n/m were the same too.

The old modem probably wasn't on DOCSIS3 but the Superhub will be. The change in performance probably only demonstrates different congestion levels between the old and new networks locally.


The old modem was on the DOCSIS 3 network, same CMTS hence same IP address when the same CPE address appeared via modem mode. Address pools are assigned per CMTS, it's not possible to move CMTS and retain the same IP address unless the DHCP pool is moved with you, which doesn't happen.

Nearly all 20Mb legacy customers are on the DOCSIS 3 network running in non-bonded mode.
Standard User Ignitionnet
(knowledge is power) Thu 14-Jun-12 09:38:26
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Re: Modem Mode Network


[re: jchamier] [link to this post]
 
In reply to a post by jchamier:
In reply to a post by Daemon66:
Can anyone explain it?


Yes, if you're using the same older router that you used with the old cable modem.

Its the hardware address (MAC address) of the router that is being passed to Virgin's DHCP server, and that looks up in its list, finds its given you an IP before, and returns the same one.

You're lucky the area you're in there are plenty of spare IP addresses, so yours wasn't re-used in that time.


Virgin's IP leases are 7 days long. To lose an address in the space of a morning would be incredibly unlucky and require VM to be running incredibly close to the wire on addresses, which they don't do.
Standard User kwikbreaks
(eat-sleep-adslguide) Thu 14-Jun-12 09:44:04
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Re: Modem Mode Network *DELETED*


[re: Ignitionnet] [link to this post]
 
Post deleted by kwikbreaks

I'd misread the inital post as saying the IP hadn't changed when the SH was first installed in normal mode.

Edited by kwikbreaks (Thu 14-Jun-12 09:48:22)

Standard User Daemon66
(newbie) Thu 14-Jun-12 13:47:30
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Re: Modem Mode Network


[re: jchamier] [link to this post]
 
In reply to a post by jchamier:
In reply to a post by Daemon66:
Can anyone explain it?

Yes, if you're using the same older router that you used with the old cable modem.

Its the hardware address (MAC address) of the router that is being passed to Virgin's DHCP server, and that looks up in its list, finds its given you an IP before, and returns the same one.

Thanks, yes that does explain it, I thought the modem would be the device to which the IP was allocated rather than my own router.
(Though VM using a MAC address that is totally under the customer's control to do their IP allocation sounds like a major security hole to me.)
Standard User kwikbreaks
(eat-sleep-adslguide) Thu 14-Jun-12 15:53:22
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Re: Modem Mode Network


[re: Daemon66] [link to this post]
 
In reply to a post by Daemon66:
(Though VM using a MAC address that is totally under the customer's control to do their IP allocation sounds like a major security hole to me.)

Why?

As it happens you can only have a few at any given time. Not sure of precise details but it's something to do with the CMTS storing the MAC/IP for each user and there only being a few slots available per user. If you fill them all you either have to wait til the oldest "times out", use an old MAC, or call TS to sort it because you will not get an IP.

Maybe ignition will feel like correcting/expanding on that.
Standard User Ignitionnet
(knowledge is power) Thu 14-Jun-12 17:03:27
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Re: Modem Mode Network


[re: kwikbreaks] [link to this post]
 
Yeah it'll only remember a very few client PC/router MAC addresses for each modem MAC, these take a week to expire.
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