DHCP Problems

[MEDA]

I am getting alot of DHCP requests from the LAN side of my cable modem (Motorola SB4200) and before my router (D-Link DI-704P). It is a private class "A", 10.x.x.x address and is not comming from my ISP which uses 24.x.x.x. Does this cable modem have the options to serve DHCP and if so how can I turn it off. The router leases the internal network with a class "c" and picks up the correct WAN address of 24.x.x.x.

SET-UP (from local loop in)= Motorola SB4200 ------>3Com TP400 hub with a work station (static assigned)----------->D-Link DI704 Router with 3 workstations (assigned by the router)

Thank for you help

 

[JackMDS]

The modem is a Modem.

Try to connect the Modem to the Router's WAN without the Station and the Hub, and see if it gone.

 

[martind1]

Originally posted by: JackMDS
The modem is a Modem.

Try to connect the Modem to the Router's WAN without the Station and the Hub, and see if it gone.

jack , doesnt it sound like the cable modem has a dhcp in it, that is giving out 10.x.x.x ips?

 

[JackMDS]

I do not think that this modem does.

 

[MEDA]

I believe that attaching the cable modem to the router will filter the DHCP requests from my internal network being that internally I run a Class "C" and the router will not allow a 10.x.x.x to pass (Will the DHCP requests still be attempting ?). I have the workstation on the WAN side of the router for traffic monitoring, and by putting the Hub and workstation on the LAN side will cause all my internal network to use the hub "slowing it down". I can filter the requests but would like to know where they are commong from.

Thanks for you replies

 

[MEDA]

Here is a reply I received from Motorola:

The modem will give the computer an IP address ONLY when one is not present
from your cable provider, and the modem uses a 192.168.100.x as the IP
address. If you have the computer connected directly to the modem and are
getting an IP address of 10.x.x.x that can only come from the cable
provider and not the modem.

They also tell me that there is no way to turn it off
?????????????????????????????????????????????????where is this 10.x.x.x comming from

 

[martind1]

is it possible that the workstation is recieving the 10.x.x.x address from the cabel company since it is before the router and it might be the way the handle unrecognized mac address?


i dont knwo im shooting at flies here.

 

[MEDA]

I set the workstation before the router to dynamic assign and it accepted a 24.x.x.x which is the IP class the ISP assigns. The 10.x.x.x still broadcasts DHCP offers.

I was wondering if it is possible that someone in my local loop (cable modem) has a DHCP server set up broadcasting this offer ????

Thanks

 

[ITJunkie]

if you just want to know where the requests are coming from just do a trace route or tracert from windows cmd line.

 

[MEDA]

I tried tracert and came up with 2 hops.

First hop = <1 <1 <1 My gateway
last hop = 28ms 7ms 14ms 10.229.50.x

what exactly does this tell me????

Thanks

 

[ITJunkie]

Originally posted by: MEDA
I tried tracert and came up with 2 hops.

First hop = <1 <1 <1 My gateway
last hop = 28ms 7ms 14ms 10.229.50.x

what exactly does this tell me????

Thanks

What it should have told you is where that DHCP server might be in relation to your network but my guess is that IP address is your workstation between your router and modem.

From the workstation between your router and your modem, open a cmd prompt and do a ipconfig /all. It should tell you the IP address of the DHCP server. I know you said you have assigned a static IP but it is not looking like that is the case.

 

[MEDA]

Yes it is!!
the 1st hop is my router so it's comming from inside my LAN?

 

[ITJunkie]

Originally posted by: MEDA
Yes it is!!
the 1st hop is my router so it's comming from inside my LAN?

You're positive that workstation has a static IP? Did you try the ipconfig /all from it?

Does it have 2 network cards?

 

[MEDA]

I change it to dynamic addressing to see if the ISP was sending it and it didn't change the offers from the 10.x.x.x network so right now it is not set static but had the same problems when it was.

ipconfig/all shows my ip address as a 24.x.x.x and my gateway 24.229.168.1
Gateway on the WAN side of my router is 24.238.64.1