still22loud
join:2006-01-28
Fountain Valley, CA |  Turning off DHCP in SB5120
Hello everyone,
I was wondering if there is a way to turn off the DHCP server on the Motorola SB5120 Modem?
I have a Linksys router that will take care of the IP assignment already.
Thank you. |
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NoVA_CoxUser
Stand back from the cage -- The RF bites
Premium
join:2004-07-06
Alexandria, VA
 ·Cox HSI
4 edits | No need to disable a modem's DHCP server. (and no way to do it either w/o a hack)
The following is from the Moto SB5101 overview: quote:
The SB5100 family of modems contain an internal DHCP server, which is active until the modem registers with the CMTS. In the case of a problem that prevents the modem from completing its registration, the modem can still give an IP address to the client PC to enable diagnostics access.
This address is given with a very short lease (around 10 seconds) so that as soon as the registration does complete the client PC obtains its proper IP address from the core network DHCP server.
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still22loud
join:2006-01-28
Fountain Valley, CA | Too bad I couldn't turn off the DHCP server on the modem. I really like using the DHCP server on the Linksys. Guess I have to call my cable company and tell them to give me another modem. Hope this is an option with Adelphia. Thanks Nova. |
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NoVA_CoxUser
Stand back from the cage -- The RF bites
Premium
join:2004-07-06
Alexandria, VA
4 edits | reply to still22loud
I don't think you understood ... as long as your modem is online ... it's DHCP server is disabled.
Your Linksys router's DHCP server will serve you just fine w/o any conflicts w/ the modem -- Moto modems are some of the best out there. |
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still22loud
join:2006-01-28
Fountain Valley, CA | Thanks for bearing with me, but I'm a little confused. When everything is up and running (modem, router, and internet), the configuration page on the Moto modem still say DHCP Server Enabled. |
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NoVA_CoxUser
Stand back from the cage -- The RF bites
Premium
join:2004-07-06
Alexandria, VA
3 edits | Yes I know ... it's confusing.
Maybe it should say "enabled but offline" or maybe "enabled but not issuing IP addresses" |
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DerEngel
join:2006-01-02
San Diego, CA
| reply to still22loud
Actually yes, you can turn off the modem's DHCP server. Motorola has this feature standard but it is hidden.
To do this, you need to enable the Factory MIB,
then using SNMP change the OID 1.3.6.1.4.1.1166.1.19.4.59.0 to integer 2, this enables a feature known "Read Only HTML". Finally, go to the modem's configuration page (»192.168.100.1/config.html) and you will now notice there is a check box next to "Enable DHCP Server", uncheck this box and click "Save".
Screenshot of the configuration page with hidden feature enabled:
»https://www.tcniso.net/shop/SB4200_UK_config.jpg |
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still22loud
join:2006-01-28
Fountain Valley, CA | Thank you Nova for trying to explain things and thanks DerEngel for showing me that it is possible to turn DHCP off. You two are the best. |
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ryan1012
@comcast.net
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Screenshot |
Also, I've been dropping my connection between my modem and my router. I just reciently baught a new Linksys Router that supports VPN and am very confident that it's not a router issue. But i've had this modem since about last August...
I've thought about just going out a buying a Linksys cable modem... Any thoughts on the Linksys vs. Motorola? |
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DerEngel
join:2006-01-02
San Diego, CA | reply to still22loud
ryan1012: It only says "DHCP Enabled" because you have to follow the instructions I posted earlier to unlock the secret feature to change it. |
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22bsti
@midco.net | reply to DerEngel
DerEngel if you dont mind my asking how do you do this and i would like to change the default lan ip address as well(to 10.0.0.2 instead of 192.168.100.1 but thats not all that iportant) |
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22bsti
@midco.net | well i figured out how to disable the dhcp server but i still dont know how to change the default lan ip address if anyone knows id be quite grateful |
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Bror1
join:2006-03-01
El Paso, TX | reply to still22loud
I'm sorry but i don't understand how to do it. i don't know what the MIB is or any of that can someone tell me how to do it step by step i would really appreciate it  |
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Johkal
Cool Cat
Premium,MVM
join:2002-11-13
Happy Valley
clubs: | MIB: Management Information Base |
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Bror1
join:2006-03-01
El Paso, TX | reply to still22loud
i still dont know what to do though help a complete noob out  |
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Johkal
Cool Cat
Premium,MVM
join:2002-11-13
Happy Valley
clubs:
·Comcast
 ·Vonage
| I don't understand his instructions either. He'll post again sometime & probably detail it.
--
Write me up for 125.......I Can't Drive 55 »redrocker.com/ »cabowabo.com/ |
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NoVA_CoxUser
Stand back from the cage -- The RF bites
Premium
join:2004-07-06
Alexandria, VA
·Cox HSI
4 edits | While admittedly interesting ... I'm still at a loss as to WHY you'd want -- or need -- to disable it.
To my understanding -- and assuming that my earlier post is accurate -- as long as the modem's online, it's not issuing IPs anyway.
Or is there more to this story ??? |
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Johkal
Cool Cat
Premium,MVM
join:2002-11-13
Happy Valley
clubs:
·Comcast
·Vonage
| You're not missing anything!
I guess like some people who would rather take their tires off the car every night as a theft deterrent. 
--
Write me up for 125.......I Can't Drive 55 »redrocker.com/ »cabowabo.com/ |
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Bror1
join:2006-03-01
El Paso, TX
| reply to still22loud
well i was reading that it will get rid or my nat problems ive already forwarded the ports and all that but im still getting the message
this is what it essentially said
" The Motorola Surfboard cable modem is generally not a problem for port forwarding because it has no "router" functions in it.
However, apparently some ISPs have found a way to "remote configure" these modems to take advantage of a legitimate feature of the modem to BLOCK the ports needed for games and filesharing.
Normally a cable modem should just "pass along" everything that comes in over the cable connection, without modifying anything. But the Surfboard has a feature built-in which will provide "Private IP addresses" to all the computers connected to it if it detects the cable Internet connection has failed, or if the "Offline" button is pressed. This is to allow multiple computers on your local network to operate as a "LAN" without a connection to the Internet. It's a legitimate "safety feature" which most home users will never need. It appears however that the feature can be turned on remotely by reprogramming the modem over the Interenet connection from the ISP. This forces the modem to provide "Private IP addresses" even when connected to the Interent, and this interfers with the modem's ability to pass along the ports without blocking them..." |
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DerEngel
join:2006-01-02
San Diego, CA
| A cable modem is a device with router characteristics (layer 3 OSI device), it is NOT a layer 2 device such as a network bridge. And if needed, I could support my claim, such as the fact that a DOCSIS cable modem uses IP addressing.
To answer 22bsti question, there is no way to change the gateway IP address (192.168.100.1) of a Surfboard modem, because its horribly hard coded in the firmware, it is however possible to change the HFC IP address (the dynamic one) using shell commands from within the modem.
And lastly, ISP's can block certain ports on a cable modem using LLC (Link Logic Control) filters. A filter can be applied in the configuration file by defining several SNMP objects. And of course, there are many ways to "undo" these types of filters. In fact, if you search the web, you may find a tutorial I wrote some time ago to do just that. |
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