Measure Twice Cut Once
Sometimes the root cause of a problem is easily found — when stepping back and looking into a mirror.
During my escapades resurrecting the computer from Hell, I had connected the system into the house network using Port 2 of the router switch. The router switch is 1 Gbps.
iperf speed test showed an average connection speed of about 95 Mbps. Basically a 10/100 Mbps connection.
I launched a web browser and accessed the router. The DD-WRT link status showed yellow for Port 2, confirming a 10/100 Mbps connection. Curiously, the WAN port link status showed green, which indicated 1 Gbps connection.
The link status puzzled me. The colors prompted me to think the router was somehow internally swapping the two switch ports. That seemed goofy because the router was functioning as expected.
My ISP connection is through a fixed wireless provider. Speeds are low compared to what many people experience and expect these days in the 21st century. The connection speed is well below 100 Mbps, at about 11.5 Mbps down and 4 Mbps up. On a good day. Those low speeds mean the router WAN link status should show yellow for 10/100 Mbps rather than green for 1 Gbps.
The next day I pulled the router from the shelf and substituted the retired-but-good-for-an-emergency WRT54GL Linksys router. The Little Router That Could. Nicely, everything is configured and the effort is little more than a straightforward swap exercise.
I decided that while the Asus router was out of the network I might use the opportunity for some special configuration backups.
Out of normal practice I downloaded and saved the current configuration. Then I pressed the router reset button for about 15 seconds. That changed the device IP address to the factory default of 192.168.1.1.
I never had downloaded and saved the default settings and this was a good time for that.
Next I configured the router with a minimal configuration. A minimal configuration that supported resetting the router to defaults and then restoring that configuration for basic operation in the house network. I downloaded and saved that configuration.
I launched a web browser to the router link status page. I connected an active Ethernet cable to each switch port, including the WAN port. The link status color for all switch ports was green.
So far so good. I attempted to restore the most recent full configuration backup file from about an hour previous. The DD-WRT firmware puked. I tried the next most recent from several weeks previous. The DD-WRT firmware accepted that file.
After rebooting all looked well and the link status for all switch ports showed green.
I removed the Linksys router and restored the Asus router to the network.
I tested the switch Port 2 and again the link status was yellow for 10/100 Mbps and the WAN port was green for 1 Gbps.
The distraction of fiddling with the router probably allowed my subconscious to reorganize. Almost immediately I realized there were two problems.
One problem was a degraded cable from the router to the main network switch. I have seen this happen inexplicably where a cable somehow goes rogue. A cable that works fine for a long time. Then poof. Conversely, perhaps the cable always was degraded but never noticed because of the slow ISP speed and the router port not being used for a few years. One way or another, shrug, and repair or replace the cable.
The other problem was conceptual and why I needed that mirror.
I forgot to look at my own house network map. The router WAN port is not connected directly to the ISP CPE but is connected to — drum roll — a 1 Gbps switch. That additional switch isolates the ISP VOIP analog telephone adapter (ATA) from the house network and connects to the ISP CPE. The router WAN port link status is correct — green for a 1 Gbps connection. The WAN port of that first switch is the actual slower 10/100 Mbps ISP speed connection, of which the switch LED confirmed my network map.