Diagnose network MTU and MSS issues on Slackware

1. When to use it

When some services work and others do not, the root cause can be a wrong MTU somewhere along the path.

MTU | MSS | ping do-not-fragment | tracepath | path issues

ip link show eth0
ping -M do -s 1472 8.8.8.8
tracepath 8.8.8.8

Adjust host names, IPs, interfaces, paths, and versions to the real system before making the change persistent.

ip route get 8.8.8.8
ss -ti | head
ping -M do -s 1400 8.8.8.8

Confirm that the output matches the expected state before considering the intervention complete.

On PPPoE, GRE, or VPN links the real fix can be a lower MTU or an MSS clamp on the firewall.

[ ] Steps completed\n[ ] Config updated\n[ ] Tests executed\n[ ] Rollback ready\n[ ] Logs checked