There are occasions where I need to monitor all traffic between two hosts with tcpdump, but I want to exclude the traffic for a particular port. E.g., I may be logged into a system via Secure Shell (SSH), but don't want to have the output of tcpdump cluttered with the SSH traffic. If you want to view traffic between the host you are logged into and a remote system, you can specify the remote system using
tcpcump host remote_host where
remote_host is the fully qualified domain name (FQDN) of the remote
system, e.g. system1.example.com, or the IP address of the remote system.
You can monitor only traffic to/from a particular port using the
port port_number parameter where port_number is
the relevant port. E.g., if I wanted to monitor
only SSH traffic with the host system1.example.com for the
standard SSH port, port 22, I could use the command below:
# tcpdump host system1.example.com and port 22
If you wish to have tcpdump monitor traffic based on two parameters, e.g.,
host name and port number in the example above, put the word and
between the parameters. However, if I wanted to monitor all traffic to/from
system1.example.com, except for traffic using port 22, I can put
not before the word port.
# tcpdump host system1.example.com and not port 22
