iptraf & tcpdump

The iptraf command is interactive colorful IP LAN monitor. It is an ncurses-based IP LAN monitor that generates various network statistics including TCP info, UDP counts, ICMP and OSPF information, Ethernet load info, node stats, IP checksum errors, and others. It can provide the following info in easy to read format:

1. Network traffic statistics by TCP connection
2. IP traffic statistics by network interface
3. Network traffic statistics by protocol
4. Network traffic statistics by TCP/UDP port and by packet size
5. Network traffic statistics by Layer2 address

Exercise : Ip Traffic Monitor ---> eth1 [ethernet] network interface  

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The tcpdump is simple command that dump traffic on a network. However, you need good understanding of TCP/IP protocol to utilize this tool. For.e.g to display traffic info about DNS, enter:

# tcpdump -i eth1 'udp port 53'