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

[videobruce]

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.
Called ISP to activate approved Modem (in case someone asks)

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

 

[videobruce]

Yes, I did have the Modem activated and yes these are approved in case someone asks.

 

[VirtualLarry]

Why wouldn't you power-cycle ALL networking devices in the chain, if you were swapping out hardware?

Seriously.

Edit: The longer version is, you need to reboot BOTH the modem and router, to re-connect the MAC-specific transparent bridge that gets set up between a cable modem and router.

 

[XavierMace]

Modems are sometime flaky about handing out DHCP leases in a timely manner.

Why wouldn't you power-cycle ALL networking devices in the chain, if you were swapping out hardware?

Seriously.

Seriously? Why would you? I've never power cycled all my equipment because I replaced my modem.

 

[VirtualLarry]

Seriously? Why would you? I've never power cycled all my equipment because I replaced my modem.

It is considered Best Practices, at least with SOHO gear.

Once a cable modem "binds" to a router, it generally MUST be power-cycled, if it is to pair with another router or PC.

 

[XavierMace]

You said ALL devices in the networking chain. Not just the router.

 

[VirtualLarry]

All of your "internet access" devices, at least.

 

[XavierMace]

Again implying rebooting something beyond the router?

 

[VirtualLarry]

In my case, it would entail the cable modem and LAN router, OR FIOS WAN router and LAN router. For *completeness, I might power-cycle my switch for good measure.

Rebooting Host PCs is generally not necessary, unless you are toggling IPv6 support at the router level.

Another reason to reboot a host PC is because Windows 10 seems to behave differently than Windows 7, and an IPCONFIG /RELEASE followed by IPCONFIG /RENEW, does NOT seem to fully populate an IPCONFIG /ALL listing, like it used to in Windows 7. So you might have to reboot the host machine to fully switch something around.

(Or remove power from the switch that the PC is connected to, such that the ethernet shows "not connected", followed by "connected", and then it will re-initialize the IP stack via DHCP and whatnot.

Some of my NAS units like to register their DNS names upon connection initialization, and if you reboot the router, but don't reboot the NAS, then the router no longer has that DNS mapping, thus if you try to browse using a Win10 PC, it won't show up, nor will it be accessible via DNS name, only IP address.

 

[XavierMace]

Rebooting the switch and clients accomplishes nothing. They know nothing of the modem's existence or that it was swapped out. Rebooting the router is generally just because that's easier than walking somebody through renewing their DHCP lease.

 

[VirtualLarry]

Rebooting the switch and clients accomplishes nothing.

It used to be, with Windows 7, you could just do an IPCONFIG /RELEASE followed by an IPCONFIG /RENEW . That no longer works properly in Windows 10. (Or the default DHCP config in Shibby Tomato 140 is br0k3.)

 

[XavierMace]

It used to be, with Windows 7, you could just do an IPCONFIG /RELEASE followed by an IPCONFIG /RENEW . That no longer works properly in Windows 10. (Or the default DHCP config in Shibby Tomato 140 is br0k3.)

Works just fine on all my Windows 10 boxes at home and I've heard zero reports of that being an issue from any of our clients. But again, swapping out the modem has nothing to do with that unless you're running a combo box. Which neither you or the OP are.

 

[videobruce]

Why wouldn't you power-cycle ALL networking devices in the chain, if you were swapping out hardware?
Seriously.

Because;
1. It was the exact same modem,
2. With the exact same WAN address,
3. When the swap was made, the existing Modem showed all LEDs as good even thou it apparently wasn't activate since I lost VoIP service, the physical swap was less than 3 seconds.
4. I wanted to see if it would work (which it should of).

 

[videobruce]

Edit: The longer version is, you need to reboot BOTH the modem and router, to re-connect the MAC-specific transparent bridge that gets set up between a cable modem and router.

The Router cares about the MAC address of the Modem???
Please explain.

 

[videobruce]

Once a cable modem "binds" to a router, it generally MUST be power-cycled, if it is to pair with another router or PC.

When it was authorized, it rebooted, but there wasn't a Router connected to it at that time.
I have done this before without this problem. This went far beyong just rebooting something. Even after I didi I still couldn't get the Router a WAN address.

 

[videobruce]

Rebooting the switch and clients accomplishes nothing. They know nothing of the modem's existence or that it was swapped out. Rebooting the router is generally just because that's easier than walking somebody through renewing their DHCP lease.

I did the Release then Renew thru the Router.
Was that necessary, I never did it before any other time I swapped Modems?

 

[mxnerd]

Use a PC instead a router to test the connection. If PC can set static WAN IP (along with default gateway IP, DNS) and get online, probably the new modem (even if it's same model) has some issues.

Make sure your PC has firewall turned on.

 

[MtnMan]

Power modem and router off.
Power on modem and wait till the lights become stable (done booting)j
Power on router.

After the router is up, can you access the modem (typically 192.168.100.1)?

 

[ylin0811]

The router received a wan ip address immediately after you modified dhcp pool settings on the router would indicate issues with dhcpd.conf file. By re-configuring dhcp pool, you are essentially re-provisioning the dhcpd.conf file which would take care any file corruption issues.

 

[razel]

It could be entirely possible that your new cable modem is plain old not working properly. Also if you did do a full cable modem reset, you may need to call them again for reactivation. They don't just get it's CM address.

 

[videobruce]

Under Setup/Basic Setup/Network Setup, I changed the Local IP & the DHCP Start IP addresses.
That caused the Router to communicate with the ISP?

The new Modem is working fine now.