Network_commands
Network hardware
Network ports
Network security
VPN
WiFi

Retroshare: fully decentralized, designed to provide maximum security and anonymity, encrypted network between your and other know computers (of known to you persons) on which various distributed services like forums, channels, chat and mail can be provided
Entirely free and open-source available on Android, Linux, MacOS and Windows. No hidden costs, no ads and no terms of service.

Come with various types of shielding to reduce interference and crosstalk.

Unshielded Twisted Pair
No shielding at all

Unshielded Foil Twisted Pair)
Each pair of wires is individually shielded with a foil, but the overall cable is unshielded

Foiled Twisted Pair
Similar to U/FTP

Foiled Unshielded Twisted Pair
The overall cable has a foil shield around all the twisted pairs, but individual pairs are not shielded

Shielded Twisted Pair
Twisted pairs with shielding. This can be individually shielded pairs or an overall shield

Foiled Foiled Twisted Pair
Each pair is foil-shielded. There’s also an overall foil shield

Shielded Foiled Twisted Pair
Each pair of wires is shielded, and there is an additional shield around the overall cable

Debian wiki
Guides for Network Configuration Using systemd-networkd
Gentoo wiki
Minimalistic Wireless Networking
Network Configuration Synchronization Points. systemd provides three target units related to network configuration
Working with systemd-networkd
More

When installing Network-Manager:
The following network interfaces were found in /etc/network/interfaces

which means they are currently configured by ifupdown:
- eth0
- wlan0
If you want to manage those interfaces with Network-manager instead
remove their configuration from /etc/network/interfaces.

Check if the network is disabled or not:

#lshw -C network
*-network DISABLED        
     description: Wireless interface
     logical name: wlp2s2
 *-network DISABLED
     description: Ethernet interface
     logical name: enp9s4

# ping -c 1 example.nl
ping: example.nl: Temporary failure in name resolution
# nslookup example.nl 9.9.9.9
;; UDP setup with 9.9.9.9#53(9.9.9.9) for example.nl failed: network unreachable.
;; UDP setup with 9.9.9.9#53(9.9.9.9) for example.nl failed: network unreachable.
;; UDP setup with 9.9.9.9#53(9.9.9.9) for example.nl failed: network unreachable.

# ifdown wlp2s2
ifdown: interface wlp2s2 not configured
# ifup enp9s4
ifup: interface enp9s4 already configured
# ping -c 1 example.nl
^C (no reaction)
# systemctl stop networking
# systemctl start networking
# systemctl status networking
● networking.service - Raise network interfaces
   Loaded: loaded (/lib/systemd/system/networking.service; enabled; preset: enabled)
   Active: active (exited) since Thu 2024-02-01 23:07:55 UTC; 19s ago
     Docs: man:interfaces(5)
  Process: 20235 ExecStart=/sbin/ifup -a --read-environment (code=exited, status=0/SUCCESS)
  Process: 21354 ExecStart=/bin/sh -c if [ -f /run/network/restart-hotplug ]; then /sbin/ifup -a --read-enviro>
 Main PID: 21354 (code=exited, status=0/SUCCESS)
    Tasks: 4 (limit: 4515)
   Memory: 2.2M
      CPU: 195ms
   CGroup: /system.slice/networking.service
           ├─20258 dhclient -4 -v -i -pf /run/dhclient.enp9s4.pid -lf /var/lib/dhcp/dhclient.enp9s4.leases -I >
           ├─20583 dhclient -4 -v -i -pf /run/dhclient.wlp2s2.pid -lf /var/lib/dhcp/dhclient.wlp2s2.leases -I >
           ├─21227 "avahi-autoipd: [wlp2s2] bound 169.254.13.48"
           └─21228 "avahi-autoipd: [wlp2s2] callout dispatcher"

# ifup enp9s4
Internet Systems Consortium DHCP Client 4.4.3-P1
Copyright 2004-2022 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/enp9s4/2e:49:61:21:b8:cf
Sending on   LPF/enp9s4/2e:49:61:21:b8:cf
Sending on   Socket/fallback
DHCPDISCOVER on enp9s4 to 255.255.255.255 port 67 interval 8
DHCPDISCOVER on enp9s4 to 255.255.255.255 port 67 interval 19
DHCPDISCOVER on enp9s4 to 255.255.255.255 port 67 interval 9
DHCPOFFER of 192.168.149.91 from 192.168.149.1
DHCPREQUEST for 192.168.149.91 on enp9s4 to 255.255.255.255 port 67
DHCPACK of 192.168.149.91 from 192.168.149.1
bound to 192.168.149.91 -- renewal in 43017 seconds.

Now there is an ethernet connection. The wireless network is still disabled:

# lshw -C network
    description: Wireless interface
  *-network
    description: Ethernet interface

When running Network-manager make sure to disable the wired and wireless networks in /etc/network/interfaces. Thereafter run systemctl restart Network-manager or better, reboot the computer
Also make sure ln -s /run/resolvconf/resolv.conf .

Also called nm-applet
This can be used to select wired and wireless networks to connect to

Use the icon in the system tray in the panel

If the connection is set to autoconnect, connections with higher priority will be preferred. Defaults to 0. The higher number means higher priority.¹⁾

When booting the computer Network-manager creates out of the bleu a new connection, with the name being the name of the networkinterfce, with a manual set IPv4 setting. IPv6 has the “Lokal link only” setting and connects to it. Even tough a Connection with both “General > Connect automatically with priority (priority set to 5)” and “All users may connect to this network” is already configured

After, for the new Connection with the name of the networkinterface, unselecting “General > Connect automatically with priority” and unselecting “All users may connect to this network” for the automatically created Connection at the next boot, after power off, Network-manager still connects to this Connection ignoring the autoconnect, priority and “all user may connect” settings

When rebooting without power off the right (priority 5) Connection is connected to

When changing the IP number and DNS settings to the settings of the already existent Connection, powering off en booting up everything seems to work fine

To make network-manager work better edit

/etc/NetworkManager/NetworkManager.conf

and change

[ifupdown]
managed=false

to

[ifupdown]
managed=true

Then do as root

service network-manager restart

or on a systemd system and Debian version is 10 or less do

 systemctl restart systemd-networkd

See also this: Debian page.

See RPi Setting up a static IP in Debian

Add

alias net-pf-10 off

to

/etc/modprobe.conf

DNS FAQ:
Q: Where can I find nslookup?
A: In the dnsutils package. dig can also be found there

Q: Error: Temporary failure in name resolution
A: Add a firewall rule for DNS. Example ufw allow to [IP of the DNS server] proto udp port 53

Q: How to make dig produce only the IP nummer of a domain?
A: dig +noall +answer {domainname]

The DNS server IP address is set in /etc/resolve.conf. See the Debian page
Permanent changes for the DNS server IP adres

Multicast IP address ranges
The computer's firewall like ufw can log a lot of multicast requests. This can be avoided

Multicast on Wikipedia
On ufw PROTO=2 is IGMP: Internet Group Management Protocol

From /var/log/messages (redacted for privacy

Jun 28 00:31:33 hostname kernel: [567987.238409] [UFW BLOCK] IN=eth0 OUT= MAC=macaddress SRC=192.168.1.1 DST=224.0.0.1 LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=872 DF PROTO=2

To block these add a rule to ufw

ufw deny from 224.0.0.1 to any

Better: Turn multicast of in the router if you do not need it

A router can be used as switch only by using only the LAN ports

If the LAN address of the router is for example 192.168.1.1 you can access and configure the router via that IP address (192.168.1.1). You will need to set the computer you are configuring the router from to the 192.168.1.0/24 network to be able to do so

You can use the switch on an other address range, x can be anything between 0 and 254 including 1 and is assigned by the upstream router
y is asigned by the DHCP server this router used as switch is connected to: 192.168.x.y For example 192.168.201.y
A computer connected to this router used as switch can be assigned to by, the upstream router, for example, IP address 192.168.201.134

Special Use Domain Name 'ipv4only.arpa'
.arpa

Network interface configure

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