Using nmap to scan a network and identify which hosts are alive

The command “nmap -sP” scans a network and identifies which hosts are alive (i.e., which IP addresses are being used) within the specified range.

In more detail, the “nmap” command is a widely used network exploration tool that can be used for tasks such as host discovery, port scanning, and service enumeration.

The “-sP” option tells nmap to perform a “ping scan,” where it sends an ICMP echo request to each host in the specified IP range and checks for responses. This method is typically faster than other scanning techniques because it only determines whether a host is up or not without gathering additional information about the host’s ports or services.

The “” argument specifies the IP range to be scanned, specifically the subnet mask “,” which corresponds to the range of IP addresses from to The “/24” suffix is a shorthand notation for the subnet mask.

Overall, the command “nmap -sP” is a helpful tool for network administrators or security professionals who need to identify which hosts are active on a particular network quickly. It can help to identify potential security vulnerabilities or unauthorized devices connected to the network.

Ubuntu – Overwrite dockerd default settings

Trying to create a new bridge on docker, we got the following error

$ docker-compose up -d;
Creating network "docker-compose_new_bridge" with driver "bridge"
ERROR: could not find an available, non-overlapping IPv4 address pool among the defaults to assign to the network

After investigating, we realized that it was due to some default limitations of docker that did not allow more virtual networks to be created. To overcome the problem, we read that we had to give access to more address space using the /etc/docker/daemon.json.

On Ubuntu that file did not exist so we created it and copied the following content to it:

  "default-address-pools": [
      "base": "",
      "size": 24
      "base": "",
      "size": 24


This configuration allowed Docker to reserve the network address space 172.80.[0-255].0/24 and 172.90.[0-255].0/24, that provided the daemon a total of 512 networks each owning 256 addresses.

To apply the changes to the daemon, we restarted it:

sudo systemctl restart docker.service;

and then we applied our changes to our docker ecosystem:

docker-compose up -d;

Qubes OS: Connect to Wi-Fi or Ethernet or another network 1

A couple of days ago we decided to give Qubes OS a go and see what it could do for a regular user. The installation was easy as it uses the same installer as Fedora, so we just created a live USB and formatted a laptop that had built in Wi-Fi.

To our surprise, we could not figure out how to change the network settings and activate an internet connection! Going to the NetworkManager (nm), even with root, would show us all fields as disabled when trying to create any new connection!

Some time passed before we realized that the NetworkManager of XFCE4 was not the way to go. After inspecting the Virtual Machines on the Qubes VM Manager, we saw that the sys-net VM was the only one that had in its hardware settings to access the Ethernet and Wi-Fi modules. So we got the hint, we needed to modify sys-net in order to connect the entire OS with its VMs to the network.

To modify the settings of the sys-net VM we needed access to the Settings Application, which was not available in the application menu. So the first thing we did, was to use the sys-net: Add more shortcuts... option under the group ServiceVM: sys-net to enable the Settings application shortcut.

In the [Dom0] Settings: sys-net window, we went to the Applications tab, on the left list we scrolled down to find the Settings option.

After selecting the Settings option, we clicked on the > button to move the Settings option to the right list.

Then we clicked on the OK button to apply the changes.

Going back to the application menu and the group ServiceVM: sys-net we could see the new option for sys-net: Settings.

Clicking on the sys-net: Settings showed us the usual settings manager for Gnome.

From there on, our job was easy, we just clicked on the Network option that gave us the window to modify all network settings. Then we selected the Wi-Fi network that we wanted to connect to, which worked without a hitch!

Finally, we had to test if the configuration was working as expected. From the application menu, under the group Domain: personal, we selected the option personal: Firefox to start the Firefox application on the personal VM.

Once Firefox started we could see that internet connection was active and everything was working as expected!