Trace DNS delegation linux
Follow full DNS resolution chain from root nameservers
dig +trace example.com
more linux
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Show established TCP connections
ss -tnp state established
Count connections per state
ss -tan | awk 'NR>1{print $1}' | sort | uniq -c | sort -rn
Traceroute with MTU discovery
mtr --report --tcp --port 443 example.com
Test MTU path
ping -M do -s 1472 -c 3 8.8.8.8
Show iptables rules
iptables -L -n -v --line-numbers