I set up my LAN about a year ago and have had no problems with it previously. I use Viasat for a satellite connection. (Cable won't service this place.) The connection comes in from the dish and connects to the Viasat router. From there, it goes to a Soekris dox running an older version of pfSense. This box has been running stably for this past year. (And, yes, I'll be updating it soon.) On the LAN side of this firewall is the house LAN, with a DISH TV Hopper and Joey, two MacMinis and two iMacs. (Maybe a printer or two as well.)
Tonight we came home and the clock on the stove and microwave were blinking 12:00 and the computers were off. Power failure. We have a standby generator that is tested weekly, but we don't know if power was off long enough for the generator to kick on or not. We just know we got home and could tell there had been a power failure.
So we set the clocks, make sure the DISH Hopper is working (and it's recording a program and doing fine). Then my wife boots her iMac. It connects to the internet without problem. I boot one MacMini before I go upstairs, then I boot my iMac.
My wife's iMac connects to the internet. My Mac Mini connects. The DISH Hopper connects. They have no problem reaching anything they need to. When I turn on wifi for my iPad and go through the LAN wifi, I can connect to the internet without trouble. (The iPad goes through an Airport Time Capsule hub, then through the firewall, then through the Viasat router. In fact, everything in the house goes through the firewall, then the Viasat router.)
So I've tested everything in the house and it all connects to the internet without a problem. (And, other than the iPad, they all connect, through hardwired ethernet cables, to a switch that has a hardwired connection to the firewall, which has a wired connection to the Viasat router and, from there, it's coax to the Viasat dish.)
Up until this power outage, the iMac in question never had trouble connecting to the internet. The only thing that's different now is that last night I installed Mojave on this computer, but it worked fine when I rebooted it. Now, it can connect to or see everything on my LAN, but nothing beyond the Viasat Router.
How is it this one iMac can't see anything beyond the LAN when it's never been a problem before and all the other systems on the LAN can see the entire internet? And, of course, what can I do to fix it?