Installing and using the nbtscan network scanner

Install command in Linux Ubuntu/Debian:

sudo apt-get install nbtscan

The Windows version can be downloaded from

Network scan example:


I will describe the possible startup keys:
-O FILENAME (output information to file)
-v (more detailed information output)
-p (port indication)
-H (generate HTTP header)
-m (MAC address indication)
-n (do not convert names to DNS, display only IP)
-t NUMBER (response time in seconds, default 1)
-v (display version nbtscan)

Blocking third-party DHCP on Cisco via DHCP Snooping

On the test, I configure DHCP Snooping on the Cisco Catalyst 6509-E to block third-party DHCP servers, on the other Cisco switches, the configuration is basically the same.

After connecting to the device immediately go to the configuration mode:


Continue reading “Blocking third-party DHCP on Cisco via DHCP Snooping”

How to disconnect SSH user

Let’s say that several users are connected through SSH.

First look at the list of online users:


Suppose the following information is displayed (where test is the user’s login):

USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
test     tty1                      11:20    1:07   0.03s  0.03s -bash
test     pts/0      11:21   13.00s  0.02s  0.02s -bash
test     pts/1      11:21    0.00s  0.02s  0.00s w

tty1 – it is a client logged in locally, that is, it is located near the computer.
pts/1 – judging for example on IP and WHAT, let’s assume that it’s us, accordingly pts/0 is the client of which we want to disconnect.

See the list of processes and their PID:

ps faux |grep sshd

At me it was displayed:

root       946  0.0  0.5  65508  5368 ?        Ss   12:00   0:00 /usr/sbin/sshd -D
root      1147  0.0  0.6  92828  6920 ?        Ss   12:01   0:00  \_ sshd: test [priv]
test      1178  0.0  0.3  92828  3384 ?        S    12:01   0:00  |   \_ sshd: test@pts/0
root      1192  0.0  0.6  92828  6592 ?        Ss   12:02   0:00  \_ sshd: test [priv]
test      1223  0.0  0.3  92828  3532 ?        S    12:02   0:00      \_ sshd: test@pts/1
test      1248  0.0  0.0  15468   956 pts/1    S+   12:25   0:00              \_ grep --color=auto sshd

We find test@pts/0 and accordingly 1178 is the required PID.

We terminate the process by specifying its ID, after which the user will immediately disconnect:

sudo kill -9 1178

See also my articles:
Configuring SSH session timeout
Installing and Configuring SSH