TCP Sanity Checks Before You Blame “The Proxy”

2026-02-09 · Networking

When connectivity fails, do not immediately tweak configs. First confirm the basics: routing, port reachability, and DNS.

# 1) Can I reach the network?
ping -c 2 1.1.1.1

# 2) Can I reach the port from outside?
nc -vz -w2 <public-ip> <port>

# 3) Does DNS return what I expect?
dig +short <name> A
dig +short <name> AAAA

Only after these are true should you investigate application-layer handshakes.