Sleepless_In_Sudbury

Then 0.4 or 0.5 or 0.253 or anything that isn't the same as the router's address or in its DHCP pool. Or shorten the LAN subnet mask on the router by one bit so the 1.x addresses are included in the subnet (though you'll need to restart all your equipment after for that to fully take). You need to pick an address that the router recognizes as being on the LAN subnet.

Change it to 0.3.

Did something get plugged in that connected switch 1 and 2 directly, i.e. other than through the router's switch? If you unplug one of the switches from the router does everything, including the stuff on the unplugged switch, start to work?

I have seen your symptom when switches not running STP are connected in a loop. Since ethernet loops never stop shutting everything down is the only fix.

If it has 2 interfaces, say Ethernet and WiFi, it will have two different MAC addresses, one for each. I guess they only wrote one on the box?

A very long time ago I worked for a US telephone company helping to operate their Internet service. One day we had an outage that took out a bunch of backbone circuits in the northeast (that we thought were diversely routed but weren't). The problem was in West Orange, New Jersey. Someone had cut out and taken a big chunk of 96 strand fiber optic cable where it came out of the ground and crossed a ravine attached to the bottom of a railway bridge. Apparently they thought it was copper, which has value as scrap, and were probably very disappointed they did all that work for something that had no value.

So I'm going to guess what you are seeing might be the result of someone starting to rip out a length of copper cable but stopping when they realized it wasn't. Maybe putting a sign saying "This is fiber optic cable" on the cable would help.

I'm going to assume it might not be HomePNA running on the coax, then, but is that the only thing you've got attached to the coax? Try outside where the telephone drop cable ends up at your house if there's nothing else inside.

That thing is a passive balun, which simply converts telephone signalling to or from the balanced twisted pair from or to the unbalanced coax, but it also claims to be a DSL filter and there is no way your modem should be downstream from that. What that suggests is that the balun is taking signal from the coax and putting it on the twisted pair, after filtering the DSL, for use by a POTS telephone. What is putting the signal on the coax is still a mystery, but there might be another balun, without the filter, at or near the telephone demarcation.

In any case it is becoming clear that the carrier is asking you to install a DSL modem when you don't have the right wiring to plug it into. You may need to ask them to come and fix their mess.

The spacing of the contracts on an RJ45 is 1mm, so when you see the 8 wire holes all in a row like the one you link to you know that will only fit wires with an insulated diameter of no more than 1mm. The diameter of 24 AWG wires with insulation is generally at or just below 1mm so those should fit in that connector. The diameter of 23 AWG wires with insulation almost always exceeds 1mm by a bit, however, so those won't fit (easily) in those holes. You instead need to find a connector that has the holes offset up-down-up-down so the larger conductors can be centered over the connector pins.

Almost all solid conductor cat5 and cat5e cable has 24 AWG wires, but most cat6 and cat6a cables claim to have 23 AWG conductors and, if they actually are that size, need connectors with the offset holes. Unfortunately, sometimes "23 AWG" is a lie and the actual conductor diameter is closer to 24 AWG, so the connectors with the straight-across holes sometimes fit on cat6. The only real way to know which connectors are best is to measure the actual diameter of the wires you are installing them on to see if they exceed 1mm.

Avoid ordering from the US, the UK or EU might be okay. The US has regulations requiring that WiFi equipment sold (or used) there be hardwired to only support the US frequency bands. Equipment sold for use in most other countries have a menu or other configuration to let you select your country. You want the latter.

What else is connected to the coax somewhere else in the house? I think the coax connector on that router is HomePNA which, if I'm remembering correctly, is like MoCA that doesn't share with cable TV. Since the router isn't connected to the DSL it must be using the coax to connect to a DSL modem that is connected to the DSL. If you can find that other box it should be plugged into the appropriate RJ11.

I see lots of T-3 timeouts and other junk in my log too, but that is DOCSIS protocol stuff that seems not to effect too much. The error counts that would be interesting would be in the "Corrected" and "Uncorrected" columns on the screen shot you posted, where all the zeros are now. They get zeroed when the modem restarts, so you need to let it run for a while to find out if there are times when the signal isn't so nice.

I think that ancient Buffalo router has 100 Mbps LAN ports and old, slow WiFi. Anything modern would be much better.

200' of wire isn't long at 1Gbps, and wire doesn't usually work sometimes and fail others, but WiFi does that. My money is on the link through the eero beacon as the problem.