I have a very simple setup with an ASUS as my edge router /24, a routed connection to my homelab Cisco layer 3 switch, and a few /24 SVIs on the Cisco. I have static routes on the ASUS pointing to the Cisco SVIs, and a default route on the Cisco pointing to the ASUS.

A few months back, lightning struck nearby the house and fried my cable modem, ASUS, and Cisco switch. I replaced all of them, but I could never correctly communicate with the homelab. When I was directly connected to the Cisco switch (3750), I had no problems and could communicate with all SVIs. I could ping back and forth between the 3750 and the ASUS (RT-AC66U_B1). But I could never SSH (or drive any other traffic) from the 3750 to the RT-AC66U, or RT-AC66U to 3750 . This has baffled me for some time, but I was bypassing it by directly connecting to the lab with an ethernet cable. I finally sat down to solve it today.

Even though my ethernet cable between the ASUS and Cisco was able to carry successful ping traffic, and tested OK with a cable tester, I decided to replace it. I apparently can still make my own ethernet cables successfully 🙂  The problem persisted after replacement.

Thinking maybe my laptop was the culprit, I tried other devices but they all exhibited the same behavior. Then I started looking at the ASUS. I had always used the Merlin firmware for my ASUS because the stock firmware was severely lacking in features. However,  the newest stock firmware looked OK when I bought the new ASUS, so I kept it. And there was my mistake. I saw a couple of posts saying that static routing wasn’t working correctly on ASUS routers.

Stock ASUS firmware 3.0.0.4_380_7743 running on my RT-AC66U_B1 does not seem to correctly handle static routes. As soon as I flashed the router to Merlin-RT-AC68U_380.68_4, all of my routing problems disappeared. I didn’t even lose my config.