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RWild
Them Or Us
Premium Member
join:2003-09-15
Cary, NC

RWild

Premium Member

[TWC] How to Disable DHCP on Surfboard Modem?

The problem I have been having with my Roadrunner connect dropping could be related to the fact that the Motorola modem is apparently competing with my dual WAN router as a DHCP server. On those rare occasions that I can actually modem, there is no option to disable LAN side DHCP. How can I do this?

sivran
Vive Vivaldi
Premium Member
join:2003-09-15
Irving, TX

sivran

Premium Member

What model of modem is this?

MacLeech
The one and only
Premium Member
join:2001-07-14
SoCal

MacLeech to RWild

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to RWild
Unless the modem is one of the SBG router models you can't disable the DHCP server. It should only be used anyway when the modem loses contact with the cable company and can't be configured in bridge mode during the sync process.

RWild
Them Or Us
Premium Member
join:2003-09-15
Cary, NC

RWild

Premium Member

I am not talking about the WAN side. When I can access the modem, one of the screens says that I can connect xx computers - that is, on the LAN side the modem wants to be a DHCP server. This means it is competing with by router as a DHCP server and will do so whenever it is powered up.

hobgoblin
Sortof Agoblin
Premium Member
join:2001-11-25
Orchard Park, NY

hobgoblin

Premium Member

said by RWild:

I am not talking about the WAN side. When I can access the modem, one of the screens says that I can connect xx computers - that is, on the LAN side the modem wants to be a DHCP server. This means it is competing with by router as a DHCP server and will do so whenever it is powered up.
What model is it?

Hob

MacLeech
The one and only
Premium Member
join:2001-07-14
SoCal

2 edits

MacLeech to RWild

Premium Member

to RWild
Click for full size
Screen from MY Motorola SB5101
said by RWild:

I am not talking about the WAN side. When I can access the modem, one of the screens says that I can connect xx computers - that is, on the LAN side the modem wants to be a DHCP server. This means it is competing with by router as a DHCP server and will do so whenever it is powered up.
I'm not talking about the WAN side either.

Standard Moto SB modems (not their SBG router modems) have a DHCP server in them that is bypassed when the modem is sync'd with the cable system correctly. The only time you should get a IP (in the 192.168 range) from the modem is when the modem is NOT connected to the cable system properly. As soon as the modem is connected to the cable system properly the modem is put into bridge mode and the DHCP server in the modem is bypassed so the cable company DHCP server can issue an IP to the computer or router connected to the modem.

The screen (»192.168.100.1/config.html) that says you can connect xx computer is showing you how many computers the modem is configured to allow online by the configuration file downloaded by the modem when it sync'd to the cable system. Otherwise it's telling you how many computers are supported by the LAN feature when the modem is not online.

Read the screen on the modem again:
quote:
When the Cable Modem is disconnected from the Internet, users on the LAN can be dynamically assigned IP Addresses by the Cable Modem DHCP Server.

RWild
Them Or Us
Premium Member
join:2003-09-15
Cary, NC

RWild to hobgoblin

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to hobgoblin
Don't know what model. It's currently dead so can't access it and I am not physically there. Won't be able to answer this for a week or so.
RWild

RWild to MacLeech

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to MacLeech
The screen looks familiar. Thanks for the explanation.

sivran
Vive Vivaldi
Premium Member
join:2003-09-15
Irving, TX

sivran to MacLeech

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to MacLeech
Is that page only accessible when the modem is not synced?

MacLeech
The one and only
Premium Member
join:2001-07-14
SoCal

1 edit

MacLeech

Premium Member

said by sivran:

Is that page only accessible when the modem is not synced?
Every Moto modem I've used always has it accessible, but I know ISPs could write custom modem configuration files to block it if they really wanted to.

pizz
Old man. Who loves video games
Premium Member
join:2000-10-27
Astoria, NY

pizz to RWild

Premium Member

to RWild
Man kinda wish i kept my Moto EMTA Didnt even know it had that feature, pretty niffty.

Vchat20
Landing is the REAL challenge
Premium Member
join:2003-09-16
Columbus, OH

Vchat20 to RWild

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to RWild
Like MacLeech stated, and it's quite simple to understand: This 'routing' feature is only enabled if the cable company allows it. TWC thus far has anything like this disabled and sends the external ip to your computer's NIC. You can ONLY connect one machine to the LAN port of the modem without a router.

The only time you will get a local 192.168.x.x ip from the modem is if it never sync'd in the first place. All modem's do this.

Once the modem syncs though, it downloads a config file that TWC has provided (you CANNOT bypass this without illegal means) which disables functionality such as this routing function.

Buy a cheap $40 router and throw it between the modem and your pc's. Save yourself a headache.