Monitoring network usage is an important part of network administration. There are a number of available tools to do the job, including tcpdump and Ethereal. But if you're looking for a different kind of tool, check out EtherApe, which displays network traffic graphically.
Instead of listing network traffic by packet, EtherApe provides a graph that displays which hosts are connecting to what. EtherApe color-codes the types of traffic, so you can determine initiated connections at a glance.
You can use packet capturing with EtherApe via the Capture menu. You can set it to capture Ethernet traffic, TCP traffic, or IP traffic, and you can specify what interfaces to listen on. By going into the Preferences, you can choose what colors to use for different types of traffic, such as WWW, SMTP, SSH, etc.
If you've captured traffic using the tcpdump utility, you can import the output from tcpdump into EtherApe to see it represented visually. This allows you to use tcpdump to capture packets, use Ethereal to inspect the packets, and use EtherApe to get a visual representation of the traffic.
By combining these tools, you can obtain a very detailed and accurate view of network traffic on your systems.
For more information about EtherApe, check out the EtherApe Web site.