Swapped Modems, same model, static WAN IP, Router couldn't reconnect

videobruce

Limp Gawd
Joined
Jan 21, 2005
Messages
412
No Firewall in Router or in O/S
Static IP addresses for all my devices except for a ATA (Obi202)
Nothing special or fancy in the LAN.
All wired except for a Laptop.

Long story short, I swapped identical Modems that gave a static WAN IP address (yes it was static!) Both had a RF connection, new one showed connected. I moved the Router cable to the new modem with no reboot of the Router.

No connection to the Internet. I rebooted the Router, still nothing. I then noted there was IP assigned. I did a DHCP release and renew twice. Still nothing.

I then reset the Router (which I didn't want to do), still nothing. No WAN IP assigned still.
I changed the LAN start IP adress from 100 to 2 since I use static IP address and after a minute the Router finally received a WAN IP address.

Questions;
1. Going from one identical Modem to another that passes an IDENTICAL IP address to the Router, is it still necessary to reboot the Router?
2. Even after rebooting, why wasn't there connectivity between the Modem & Router, even thou the Modem 'Link' LED showed connected and with activity?
3. After the Router reset, is spite of the LAN starting address at 100 which was outside of the static IP's of my devices, why didn't the Router get the WAN address from the Modem??

Win7
Spectrum ISP
Zoom 5341J Modem
TP-Link WDR-3600 Router running dd-wrt firmware
 
What Vengance_01 said. Especially so since you have a static IP from your ISP, most likely they will need the information from the modem, such as MAC address for you to gain access to their network. Just call them up and say you switched modems and you should be good. Does your ISP modem do NAT, and then you have your own router behind that also doing NAT? Additionally, you want to make sure your modem is configured for bridge mode if you are controlling the routing and NAT on your own.

  1. Moving the cables from the old modem to the new modem can still not properly flush ARP entries. When you move this stuff around, you definitely want to rebooth both the modem and router.
  2. There should be link connectivity, but that doesn't mean IP connectivity will be successful. Two different things
  3. If the ISP modem is doing NAT, it's important that your inside LAN of your router and the transit network between the modem and the router is not in the same subnet. If the ISP modem is in bridge mode, you just configure your public WAN IP address on your router.
 
Yes (of course) to the 1st question, I've done this a many times over the years before, never with issue.

No idea about NAT with the Modem since there is no user control other than changing the password. Unless that is something they do or can do.

I never change the subnet. The only change are the last set of numbers 192.168.1.xxx

I should of reworded the "connectivity" better. I was referring to the fact the Modem showed 'communication' with the Router (Link light flashing), but apparently not the other way around, no WAN, or even the time established..
 
How long did you leave everything off? I have TWC/Spectrum as well and every time with my old consumer Router ( Netgear or Dlink), I had to reboot it. Since I moved to a Cisco 2911 Router and I replace a modem do to whatever, I just leave the modem turned off for a while, Register the new one, wait 20 minutes, then connect the new modem. I am on my 3rd modem, but only lost 1 due to malfunctions.

Have you hooked a Computer directly into the modem and programmed it to see if the computer can get online? Could be an issue with the Router.
 
The new Modem was powered on. It was not connected to the Router or a PC.
The old Modem was still connected to the Router.
Except for the 'Link" light, all four indicators were lit in a normal/active state making one think it was already activated.
I called gave him the MAC address, he activated it, I watched the lights cycle, the call was disconnected (I have VoIP and was using that for the call).
I moved the Router cable from the old to the new, NOT rebooting the Modem (purposely), checked for Internet access, but nothing.
Rebooted the Router, still nothing, rebooted everything, still nothing.

Off time was 20-30 seconds.

I eventually got things back, but never had this problem before after 5 or 6 other swaps throughout the years.
 
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