Monitoring

Tools

Network

• nload - interface traffic graphs
• bwm-ng - interface traffic stats (no graph)
• jnettop - IP flows, TCP and UDP
• tcptrack  - TCP only
• btop - also shows network stats
  
• conntrack - tracked connection by kernel
  
• netstat or ss - show established local connections and listening ports
  

Zabbix

Custom checks

ping -c 10 -A -n -q -w 10 192.168.1.1 | awk -F/ '/rtt/ { print $5 }'