Rookie

Lost a DHCP assigned IP?

I'm looking to the community to understand what happened to my TWC internet (upstate NY).

For many years internet came to the house via an Arris TM402G/110.  During that time I ran Cat-5 to a 10/100 switch and from there connected two gateway/routers.  Each device was able to request and renew a leased IP and everything was fine.

On January 2nd 2017 we switched to a customer owned cablemodem an Arris (SP6190).  Since then only one device on the switch can secure a leased IP, as far as I can tell any other device is ignored completely.  I'm certain they both work because if I power off the cablemodem for 'a while' (tm) and connect the other one it gets a lease just fine.

 

What do I have to do to get my 2nd IP back?

 

Thanks

9 REPLIES 9
Proven Sharer

Re: Lost a DHCP assigned IP?

Each TWC residential customer only gets ONE pubiic IP address for their modem.  If you are an IP wizard you'll know how to program your first and second router IP address settings to build two isolated LANs.  If not, we can help you once we understand your networking goals and  the specific make/models of equipment you are using to get there.

Expert

Re: Lost a DHCP assigned IP?

You won't... TWC only allows a single outside IP and you must use a router, not a switch for various devices.  Only one device will work at a time with what you have now.

  You can use the switch after the router to expand to more than 4 ports, You may want to put the devices that need tthe faster connections on 3 ports then the switch on the 4th port for slower ones.

 The router does nat and dhcp assignments, set the DHCP start at 192.168.1.100, any static ip devices at 192.168.1.99 on down, the gateway would be 192.168.1.1 etc

 

Rookie

Re: Lost a DHCP assigned IP?

Thank you both for the quick reply.

 

The only explanation I can come up with for this is that TWC was somehow not aware that two separate devices were connected simultaneously each getting it's own lease.  The setup I described was working and working well.

 

I was really hoping the answer would be different, probably should not have messed with what I have even though the cablemodem rental was costing me and extra $10 a month on my bill.

 

I was simply trying to avoing any double NATing because it can screw with VPN's.

Expert

Re: Lost a DHCP assigned IP?

Without a router you have no NAT. TWC assigns public IP's to the mac address of the device. on old cmts firmware you could get different ones with 2 device Mac's

 You need your own router not an all in one device, even if you own it

TWC messes with router settings if they can get into it

 

Highlighted
Rookie

Re: Lost a DHCP assigned IP?

"Without a router you have no NAT

Right, and with two routers connected in series you get double NAT.

 

"old cmts firmware you could get different ones with 2 device Mac's"

I had two routers each with it's own IP for a very long time and as recently as 6 days ago.  Are you saying that the CMTS was replaced or firmware was upgraded the same day I activated a customer owned modem?

 

"You need your own router"  Roger that, I have two.

 

I was hoping for some feedback on how to get TWC/Spectrum to give me back what I had.  So far the only answer i have received from TWC/Spectrum involves purchasing a block of fixed IPs from business class.

Proven Sharer

Re: Lost a DHCP assigned IP?

In the "Before" config the two routers were actually in parallel, since both were connected to the modem through the LAN switch.  Each router provided NAT only for devices connected to its LAN ports and WiFi.

Proven Sharer

Re: Lost a DHCP assigned IP?


@karlbeckman wrote:

In the "Before" config the two routers were actually in parallel, since both were connected to the modem through the LAN switch.  Each router provided NAT only for devices connected to its LAN ports and WiFi.


You got lucky, and the modem you were leasing overlooked the fact there were two IP's assigned to it.  I recall that in the early days, those who used hubs downstream of their cabel modem would be assigned multile public IPs in their home.  I assume that once broadband in the home grew, the cable companies realized they had to do something.  You arrangement probably fell through the cracks.

 

You already have the answer, albeit the one you don't want.  I would imagine if you want two public IP addresses, you will need to pay for two services.

Proven Sharer

Re: Lost a DHCP assigned IP?

If the original poster @h_bailey agrees, this can be marked "Solved."
Rookie

Re: Lost a DHCP assigned IP?

No objection