conntrack — connection tracking

Cheat sheet

• sudo conntrack -L connections
• sudo conntrack -E events in real time
• sudo conntrack -S drops / insert_failed
• sudo conntrack -D -s 10.0.0.5 reset a source's connections
• cat /proc/sys/net/netfilter/nf_conntrack_{count,max} table load
• sudo sysctl -w net.netfilter.nf_conntrack_max=262144 raise the limit

Options

Flag	Meaning
-L	list connections (the tracking table)
-E	real-time event stream
-S	per-CPU statistics (drops, insert_failed)
-D	delete entries (matching a filter)
-p / --dport / -s / -d	filter: protocol / port / source / destination
--state	filter by state (ESTABLISHED, TIME_WAIT…)