lsof -i output *:*?

Question

What is the meaning of the output under the NAME tag of the lsof -i command when it appears as such *:*

Example output:

Answer 1

The UDP *:* means you have processes on your system listening on all network interfaces for IPv4 UDP packets:

• All IPv4 Addresses are represented by a * on the left of the colon
• All ports are represented by a * on the right of the colon

You can test this by sending a batch of 5 UDP packets to one of your local addresses with netcat:

$ echo "data" | nc -w1 -u 127.0.0.1 1-5

While using lsof in repeat mode to show the UDP connection activity:

$ lsof -r1 -iUDP -P -n  | grep -E "^nc"
nc         3197           root    3u  IPv4 0x614d3be71aa32a89      0t0  UDP 127.0.0.1:57137->127.0.0.1:2
nc         3197           root    3u  IPv4 0x614d3be71b503dc9      0t0  UDP 127.0.0.1:62455->127.0.0.1:3
nc         3197           root    3u  IPv4 0x614d3be71bdbe351      0t0  UDP 127.0.0.1:52982->127.0.0.1:4
nc         3197           root    3u  IPv4 0x614d3be71b6335b9      0t0  UDP 127.0.0.1:61450->127.0.0.1:5