Modify

NICs

nmtui	Provides a text user interface to easily modify network interface settings through NetworkManager.
ifconfig <interface> <IP_address> netmask <netmask>	Assigns an IP and netmask
ip link set eth0 address 00:11:22:33:44:55	Change MAC address (temporarily)
ifconfig <interface> up|down	Activates/deactivates an interface
ip addr add <IP_address>/<netmask> dev <interface>	Adds an IP and netmask
ip addr del <IP_address>/<netmask> dev <interface>	Deletes an IP from a network interface
ip link set <interface> up|down	Brings a network interface up or down
ip link set dev <interface> name <new_name>	Changes the name of a network interface.
ethtool -G <interface> rx <value> tx <value>	Changes the RX and TX ring buffer sizes for an Eth interface.
ethtool -s eth0 speed 100 duplex full autoneg on	Change speed, duplex mode, auto-negotiation
iwconfig <interface> essid <ESSID>	Sets the ESSID (network name) for a wireless network interface.
iwconfig <interface> mode <mode>	Set operating mode of a wireless interface (e.g., Managed, Master, Monitor).
iw <interface> set type <type>	Changes the type of a wireless interface (e.g., managed, monitor) using the iw command.
ip route add|del via dev	Adds or deletes a route to a network or host via a specified gateway
ethtool -s <interface> speed <speed> duplex <duplex> autoneg on|off	Changes the speed, duplex mode, and autonegotiation settings for an Ethernet interface
nmcli device modify <interface> ipv4.addresses <IP>/<netmask> ipv4.gateway <gateway> ipv4.dns "<dns_servers>"	Modifies the IP address, gateway, and DNS settings for a network interface using NetworkManager

Adds or deletes a route to a network or host via a specified gateway:

ip route add|del <destination> via <gateway> dev <interface>

Changes the speed, duplex mode, and autonegotiation settings for an Ethernet interface:

ethtool -s <interface> speed <speed> duplex <duplex> autoneg on|off

Modifies the IP address, gateway, and DNS settings for a network interface using NetworkManager:

nmcli device modify <interface> ipv4.addresses <IP>/<netmask> ipv4.gateway <gateway> ipv4.dns "<DNS_servers>"

Config Files (persistent changes)

Edit /etc/network/interfaces (Debian/Ubuntu):

Add lines like auto eth0, iface eth0 inet static, address 192.168.1.100, netmask 255.255.255.0.

Edit /etc/sysconfig/network-scripts/ifcfg-eth0 (Red Hat/CentOS): Modify BOOTPROTO, IPADDR, NETMASK, etc.

ARP

arp -d <IP>	Deletes an ARP
ip neigh del <IP>	Deletes an ARP
ip neigh del <IP_address> dev <interface>	Deletes an ARP entry for the specified IP
arp -s <IP> <MAC>	Adds a static ARP entry
ip neigh add <IP> lladdr <MAC>	Adds a static ARP entry
ip neigh add <IP> lladdr <MAC> nud permanent dev <interface>	Adds a static ARP entry

Replaces or adds an ARP entry. If the entry for the specified IP address exists, it is updated; otherwise, a new entry is added:

ip neigh replace <IP> lladdr <MAC> nud permanent dev <interface>

Removes ARP entries matching the <selector>, which can be an IP , network, or all to clear the entire ARP cache:

ip neigh flush <selector>

DNS

Direct File Editing

Edit /etc/resolv.conf for temporary changes: Add or modify nameserver lines to specify DNS servers. Add or modify search lines to set search domains. Changes might not persist after network restarts or DHCP updates. sudo vi /etc/resolv.conf

Modify nsswitch.conf for DNS Lookup Order /etc/nsswitch.conf: This file controls the sources from which names are resolved (e.g., hosts, passwords). For DNS, you might modify the hosts: line to change the lookup order. Example command to edit: sudo vi /etc/nsswitch.conf

Network Manager (if applicable)

Use GUI or command-line tools like nmcli or nmtui to modify DNS settings via Network Manager. Changes usually persist across reboots and network changes.

nmcli: For systems using NetworkManager, nmcli can modify DNS settings. To set DNS servers on a specific connection: nmcli con mod <connection_name> ipv4.dns "<DNS_servers>" nmcli con mod <connection_name> ipv6.dns "<DNS_servers>"

To reload the connection and apply changes: nmcli con up <connection_name>

dhclient

dhclient: If your system uses DHCP to obtain network settings, including DNS, you might need to modify the DHCP client configuration to change DNS behavior. \

The configuration file might vary, but commonly /etc/dhcp/dhclient.conf is used. \

You can specify prepend domain-name-servers <DNS_server_IP>; to add custom DNS servers. \

Example command to edit dhclient.conf: sudo vi /etc/dhcp/dhclient.conf

Distribution-Specific Tools

Debian/Ubuntu: Use resolvconf to manage resolv.conf dynamically.

Red Hat/CentOS: Use systemd-resolved to manage DNS configuration. systemd-resolve or resolvectl: On systems using systemd-resolved, this tool manages DNS settings. \

To set global DNS servers: ` sudo systemd-resolve --set-dns=<DNS_server_IP> --interface=<interface_name>

To set DNS domains for searches: ` sudo systemd-resolve --set-domain= --interface=<interface_name>

Routing Tables

ip route add <network>/<prefix> via <gateway>	Add a route
route add -net <network> netmask <netmask> gw <gateway>	Add a route
ip route del <network>/<prefix>	Delete a route
route del -net <network> netmask <netmask>	Delete a route
ip route add default via <gateway>	Change the default gateway
route add default gw <gateway>	Change the default gateway
ip route flush all	Flush all routes

Config Files (persistent changes)

Edit /etc/network/interfaces (Debian/Ubuntu): Add post-up or pre-up commands to execute routing commands after interface activation.

Edit /etc/sysconfig/network-scripts/route-<interface> (Red Hat/CentOS): Add routing rules directly to configuration files.

Sockets

Adjusts the range of ports available for user-space applications:

sysctl -w net.ipv4.ip_local_port_range="1024 65535"

Enables reuse of sockets in TIME-WAIT state for new connections, affecting how sockets are managed:

sysctl -w net.ipv4.tcp_tw_reuse=1

Uses Uncomplicated Firewall (ufw) to allow or deny access to specific ports on Ubuntu and other systems:

ufw allow|deny <port>

Allows incoming TCP connections on a specific port. Modify rules to control access to sockets:

iptables -A INPUT -p tcp --dport <port> -j ACCEPT

The easiest way to open and close ports is to kill/disable the process/service using it. Otherwise, you can make firewall/iptable rules to block/allow/etc.