Failed access to a single website - modem/router troubleshooting guide

summary of issue - on or about 17 Dec 2020 I could not longer access the www.tsp.gov website from any device that was using my home network wifi (desktop, iphone, ipad) via chrome, edge or avast .  I could access the site from my phone if I turned off wifi. I had not made any changes to my modem or router and only that website was an issue. I was able to access all other websites 

following is a recap of how I resolved the issue (windows 10, spectrum cable modem, c2300 router)

1st I had to figure out where to start.  Assumed it was either website, router or ISP.  As this is a popular website and no tweets or posts about any issues on the web I decided to start with my router (TP LINK).  

TP Link reps (on a saturday) were very responsive and helped me confirm it was in fact a router issue.  This was determined by bypassing the router and connecting my desktop directly to the cable modem via ethernet.  In this configuration I could access the site. things they had me try that did not work

- change to google DNS 8.8.8.8, 8.8.4.4

- change MTU to 1400 (from 1500)

after 2 hours they were unable to resolve beyond that so plan was to escalate on monday.

I was impatient so decided to troubleshoot on my own now that i knew it was a router issue.

i connected an old linksys router to the cable modem and was able to connect with the website.

when i connected my tplink router and restored the settings from a saved file it would not work

the following worked (need to be patient for each step to complete as it can take a couple of minutes - each)

- power off both cable modem and router for at least a minute

- power on the cable modem and wait until is settles

- connect router and power on.

- hard reset of router (press and hold reset for 10 seconds)

- soft reset of cable modem (need to wait until router settles). took about 2 minutes for the internet light on router to turn from orange (no connection) to white (connection)

- log into router 

-do a fresh set up.  it did not work when i restored from saved configuration file

- i used clone MAC address 

I still have no idea about the root cause of not being able to access only the one website.