Openbsd list open tcp or udp ports

Posted by Vivek on Tuesday November 7, 06 @6:20 am

Q. How do I find out openbsd open tcp or udp ports?

A. Use netstat command. It show network status in various network-related data structures. There are a number of output formats, depending on the options for the information presented. Another option is to use nmap from remote computer. However do not use nmap to scan remote host if you are not authorized person.

Task: Display tcp and UDP open port

Type netstat command as follows :

No need to login as root user.

$ netstat -nat
OR
$ netstat -at | grep LISTEN
Output:

$ netstat -at | grep LISTEN
tcp        0      0  *.291                  *.*                    LISTEN
tcp        0      0  localhost.submissi     *.*                    LISTEN
tcp        0      0  localhost.smtp         *.*                    LISTEN
tcp        0      0  *.time                 *.*                    LISTEN
tcp        0      0  *.daytime              *.*                    LISTEN
tcp        0      0  *.auth                 *.*                    LISTEN
tcp6       0      0  *.ssh                  *.*                    LISTEN
tcp6       0      0  localhost.submissi     *.*                    LISTEN
tcp6       0      0  localhost.smtp         *.*                    LISTEN
tcp6       0      0  *.time                 *.*                    LISTEN
tcp6       0      0  *.daytime              *.*                    LISTEN
tcp6       0      0  *.auth                 *.*                    LISTEN

Only display tcp IPv4:
$ netstat -f inet -atOutput:

Active Internet connections (including servers)
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)
tcp        0      0  openbsd.23087          resolver1.opendn.domai TIME_WAIT
tcp        0      0  openbsd.22            dsl-KK-dynamic-1.32789 ESTABLISHED
tcp        0    448  openbsd.22            dsl-KK-dynamic-1.32786 ESTABLISHED
tcp        0      0  *.22                  *.*                    LISTEN
tcp        0      0  localhost.submissi     *.*                    LISTEN
tcp        0      0  localhost.smtp         *.*                    LISTEN
tcp        0      0  *.time                 *.*                    LISTEN
tcp        0      0  *.daytime              *.*                    LISTEN
tcp        0      0  *.auth                 *.*                    LISTEN
Active Internet connections (including servers)
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)
udp        0      0  localhost.biff         *.*
udp        0      0  *.syslog               *.*

Show information about the network interface:
$ netstat -iOutput:

Name    Mtu   Network     Address              Ipkts Ierrs    Opkts Oerrs Colls
lo0     33192                                6     0        6     0     0
lo0     33192 loopback    localhost.nixcraf        6     0        6     0     0
lo0     33192 localhost.n localhost.nixcraf        6     0        6     0     0
lo0     33192 fe80::%lo0/ fe80::1%lo0              6     0        6     0     0
pcn0    1500        00:0c:29:7b:66:72      560     0      485     0   124
pcn0    1500  75.126.68.4 openbsd.nixcraft.      560     0      485     0   124
pcn0    1500  fe80::%pcn0 fe80::20c:29ff:fe      560     0      485     0   124
pflog0* 33192                                0     0        0     0     0
pfsync0 1460                                 0     0        0     0     0
enc0*   1536                                 0     0        0     0     0

Show information about the specified interface pcn0
$ netstat -I pcn0

See how to use nmap to find out remote system open port. Read man page of netstat for more information.

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