Networking
The way computers talk to one another.
Every computer on a network has it's own address. IP address -- Internet Protocol
https://www.google.com/search?q=ubuntu+gnome+3+change+IPs ubuntu gnome 3 change IP - Google Search https://www.lifewire.com/how-to-configure-networking-in-gnome-4682592 How to Configure Networking in GNOME
There are ip address ranges that are designated for internal (private) networks.
192.168.1.x is a common one.
Open Ports
On a linux machine you can install netstat to see what ports are currently open:
sudo apt install net-tools
netstat -pan | egrep " LISTEN "
netstat -tulnp
t – Show TCP u – Show UDP l – Show only listening processes (netstat can show both listening and all established connections, i.e. as a client too) n – Do not resolve network IP address names or port numbers p – Show the process name that is listening on the port
Similar to netstat, but the focus is on processes:
ss -nutlp
lsof -i
via: https://www.thegeekdiary.com/centos-rhel-how-to-find-if-a-network-port-is-open-or-not/
To scan open ports from another (external) machine that's on the same network
nmap [ip of machine to scan]
Common Ports
By convention, common services utilize specific ports to publish and connect to the service. Some examples include:
SSH 22 DNS servers 53 tcp potential trojan (probably dns) ipps 631 Internet Printing Protocol over HTTPS
Firewall
Firewalls block external traffic from entering internal networks and hosts.
iptables
iptables -xvn -L
DNS
To resolve a name associated with an IP address, try nslookup:
nslookup 129.79.5.100
Traceroute
sudo apt install inetutils-traceroute
Traffic Analysis
Wireshark
To see what is happening on a network, use wireshark
https://www.wireshark.org/ Wireshark · Go Deep.
sudo apt install wireshark
https://jvns.ca/blog/2018/06/19/what-i-use-wireshark-for/
To see statistics on TCP connection duration:
'Statistics' -> 'Conversations'
Other tools
https://www.reddit.com/r/networking/comments/78mtfj/looking_for_an_open_source_network_traffic/ Looking for an open source Network Traffic Analyzer : networking
https://github.com/robcowart/elastiflow GitHub - robcowart/elastiflow: Network flow analytics (Netflow, sFlow and IPFIX) with the Elastic Stack http://pmacct.net/ pmacct project: IP accounting iconoclasm https://gitlab.com/thart/flowanalyzer Manito Networks / flowanalyzer · GitLab https://www.ntop.org/ ntop – High Performance Network Monitoring Solutions based on Open Source and Commodity Hardware.
Interface Configuration
Often it's pretty straightforward to use a GUI. If you want to configure an interface via a CLI, it's necessary to know where the OS stores the configuration settings. This varies from OS to OS.
Ubuntu
Find the interface in use
ip address
enp0s25
The netplan configuration is located in /etc/netplan
cd /etc/netplan
sudo cp 01-network-manager-all.yaml 01-network-manager-all.yaml.bak
Modify the netplan configuration.
sudo vi 01-network-manager-all.yaml
add a section like:
ethernets:
eno2:
dhcp4: no
addresses: [192.168.1.200/24]
gateway4: 192.168.1.1
nameservers:
addresses: [8.8.8.8,4.2.2.2]
Then
sudo netplan apply
to apply the configuration and changes to affect.