I use the following command to check on the number of connections from IP’s at port :80
netstat -ant | awk '$4 ~ /:80$/' | awk '{print $5}' | awk -F: '{print $1}' | sort | uniq -c
Also, the following code is used to check the various state of tcp connections and the number of connections associated with each state:
netstat -ant | awk '{print $6}'| sort | uniq -c | sort -n
Some examples on egrep and awk
In case you want to know the service listening to any port#, say port 139
egrep '' /etc/services
You get the same output as above using awk as follows:
awk '$2 ~ /^139/tcp/ {print $1,$2}' /etc/services
Though egrep is easier one, I somehow love using awk for text manupulations..