USG not Getting IP From New ISP

[Slaters Kustum Machines]

I have a customer that is using a USG with a cable modem that is working perfectly fine. Just a DHCP connection, nothing special. They are moving to a new ISP with a Fiber connection, again, just DHCP nothing special, however the USG will not get an IP from the new ISP connection, but if I plug my laptop directly into the ONT it gets an IP and internet works as expected. I have tried to factory default the USG and I get the same results. Anybody run into this before? I will be back onsite tomorrow to try to get this working again.

 

[YeOldeStonecat]

Assuming updated firmware and Unifi controller on this USG?
Kill the power on the fiber gateway for a few minutes so it dumps the MAC address of any prior device that connected to it?

The Unifi gateways are typically a little slow to obtain an IP from DHCP. Takes a minute or three.
Try rebooting the gateway while it's uplinked to the USG.
A minute later..if nothing, reboot the USG.
A minute later..if not...go into properties of the USG (within the Unifi controller)..Config, down below..Advanced..and try setting the MTU manually to 1500 (default is auto..it's under MSS clamping). And then repeat above reboot steps. Not knowing your ISP specifically...doubt it's PPPOE so 1492 shouldn't be needed but maybe MTU isn't being negotiated well.

 

[Slaters Kustum Machines]

Assuming updated firmware and Unifi controller on this USG?
Kill the power on the fiber gateway for a few minutes so it dumps the MAC address of any prior device that connected to it?

The Unifi gateways are typically a little slow to obtain an IP from DHCP. Takes a minute or three.
Try rebooting the gateway while it's uplinked to the USG.
A minute later..if nothing, reboot the USG.
A minute later..if not...go into properties of the USG (within the Unifi controller)..Config, down below..Advanced..and try setting the MTU manually to 1500 (default is auto..it's under MSS clamping). And then repeat above reboot steps. Not knowing your ISP specifically...doubt it's PPPOE so 1492 shouldn't be needed but maybe MTU isn't being negotiated well.

Excellent. Both are on the latest updates and no PPoE. I'll try your suggestions, thanks.

 

[Your PCMD]

Make sure the USG (I assume its not a Pro) has a different IP (default is 192.168.1.1 which is the same for some ISP's) as the modem. Also, check the subnet. I've had issue's with the subnet in the past so you'll never get DHCP to work until you config the USG.

Easy way to do that is to set a laptops IPv4 to 192.168.1.10/24 and plug it to the USG, open a browser and go to the USG's IP and set it up BEFORE connecting it to the modem.

 

[Slaters Kustum Machines]

Make sure the USG (I assume its not a Pro) has a different IP (default is 192.168.1.1 which is the same for some ISP's) as the modem. Also, check the subnet. I've had issue's with the subnet in the past so you'll never get DHCP to work until you config the USG.

Easy way to do that is to set a laptops IPv4 to 192.168.1.10/24 and plug it to the USG, open a browser and go to the USG's IP and set it up BEFORE connecting it to the modem.

Correct, not a Pro. The IP from the ISP started with 38.x.x.x. I don't recall the rest of the octets. When I logged into the USG while connected to the new ISP connection I got an error "Gateway is unable to connect to the internet". I think @YeOldeStonecat is on to something with power cycling their Gateway since I connected my laptop to the connection first to see if I had a connection. I have worked with this ISP (IMoN) and never had that issue so the simplest task slipped my mind. They client didn't confirm our appointment today so I'll follow up once I get back onsite.

 

[Markverhyden]

When I'm working with public dhcp I'll do a dhcp release from CLI. Works most of the time. Biggest problem I have with ISP's doing public DHCP is that they often require running some setup to clear the previous MAC and approve the new one. Charter does this.

 

[Slaters Kustum Machines]

Power cycled the gateway this morning and pulled an IP immediately. Sometimes the simple things just elude me........Thanks everyone.

 

[YeOldeStonecat]

Power cycled the gateway this morning and pulled an IP immediately. Sometimes the simple things just elude me........Thanks everyone.