Solved Certain websites will not load

[BSOD2600]

RT-AC87U on 384.13_10.



First, yes I realize the router and firmware are EOL. Something newer is on the way in a week or two.

Second, it appears that a handful of notable websites do not load (connection timeout or connection reset) for any device on the LAN. PC, Mac, or mobile – all the same result of failure. Websites such as https://wellsfargo.com/ https://www.becu.org/ yet other sites like https://www.chase.com/ or https://www.virustotal.com/ load just fine. It’s only a small fraction of every day sites which will not load. They all get valid DNS resolution.

Third, the problem started mid-last week. No, I haven’t made any changes to the network or configs.

Fourth, Looks somewhat like the same problem in this thread: https://www.snbforums.com/threads/weird-website-issue-seem-to-be-something-with-the-router.59880/

Fifth, bypassing the router (direct connection to cable modem to PC; VPN connection from PC) makes all the aforementioned sites functional.

Sixth, factory defaults makes all the aforementioned sites functional. Thus appears to be something specific to the router. Restoring the backed up config, breaks the sites again. Thus, appears to be something specific in the current settings which is the culprit.

Seventh, disabling AiProtection and Firewall (don’t use any other advance filtering type settings) does not fix the problem.





Obviously I’m trying to not have to rebuild all the configs from scratch AND I really want to figure out what broke.

Any ideas what might be going on?

 

[Wade Coxon]

Is the MTU in your router set correctly? This is a common symptom of an oversized MTU.

 

[AndreiV]

Restoring the backed up config, breaks the sites again.

You answered your own question.

 

[BSOD2600]

Is the MTU in your router set correctly? This is a common symptom of an oversized MTU.

Funny you should ask. A few weeks ago I did try changing it from the default of 1500 to 1472 (largest without Packet needs to be fragmented but DF set) but eventually changed it back at 1500. The UI still shows 1500. Any way to check whats really set in the config?

 

[BSOD2600]

You answered your own question.

Right.
It's more about understanding why its broken than just blindly rebuilding the configs. Helps myself in case happens again, along with the community.

 

[BSOD2600]

Solved.

Changed the MTU from 1500 to 1472, clicked save. sites still broken. Reboot router. still broken.
Changed MTU back to 1500. still broken. Reboot router. All the aforementioned sites are functional.

Seems to be a bug with how the firmware handles changing MTU.... but since its EOL, know won't get fixed.

 

[john9527]

Keep track of your WAN ip address assigned by your ISP. Another common cause of only some sites being broken is that your ISP is assigning you an address that has been blacklisted by those sites. (Each time you reboot you may obtain a different address depending on the ISP).

 

[Tech9]

I had to shut down one cable modem once for about 1h due to emails originated from it's IP were getting rejected from the recipient's firewall.