The Netstat command displays active connections, ports, IP routing table and much more. When running the command you can be overwhelmed by the output, especially on Unix/Linux based systems.
To filter out the noise, you can use certain syntax to provide only the results you want to see. For example I use the following to see only SMTP port 25 connections:
netstat -an -p TCP | find ":25"
To see what connections are coming from a specific IP address say 192.168.1.26
netstat -an -p TCP | find "192.168.1.26"
On a Linux system you can simply use grep e.g.
netstat -an -p TCP | grep "192.168.1.26"
netstat -tulpn | grep :53
Here is the complete example list from the Windows help file:
The usual windows netstat output:
Displays protocol statistics and current TCP/IP network connections.
NETSTAT [-a] [-b] [-e] [-n] [-o] [-p proto] [-r] [-s] [-t] [-v] [interval]
-a Displays all connections and listening ports.
-b Displays the executable involved in creating each connection or
listening port. In some cases well-known executables host
multiple independent components, and in these cases the
sequence of components involved in creating the connection
or listening port is displayed. In this case the executable
name is in  at the bottom, on top is the component it called,
and so forth until TCP/IP was reached. Note that this option
can be time-consuming and will fail unless you have sufficient
-e Displays Ethernet statistics. This may be combined with the -s
-n Displays addresses and port numbers in numerical form.
-o Displays the owning process ID associated with each connection.
-p proto Shows connections for the protocol specified by proto; proto
may be any of: TCP, UDP, TCPv6, or UDPv6. If used with the -s
option to display per-protocol statistics, proto may be any of:
IP, IPv6, ICMP, ICMPv6, TCP, TCPv6, UDP, or UDPv6.
-r Displays the routing table.
-s Displays per-protocol statistics. By default, statistics are
shown for IP, IPv6, ICMP, ICMPv6, TCP, TCPv6, UDP, and UDPv6;
the -p option may be used to specify a subset of the default.
-t Displays the current connection offload state.
-v When used in conjunction with -b, will display sequence of
components involved in creating the connection or listening
port for all executables.
interval Redisplays selected statistics, pausing interval seconds
between each display. Press CTRL+C to stop redisplaying
statistics. If omitted, netstat will print the current
configuration information once.
Powershell is a little different:
netstat -a -n | find `"443`"
To prevent PowerShell from stripping the double quotes use the grave accent (`) to escape them. You can also use the –% parameter to perform the escape.
nestat -a -n | find --% "443"