Network

Configuring Network using Netplan

• Edit /etc/netplan/*

• Apply config: sudo netplan apply

• https://linuxconfig.org/ubuntu-22-04-network-configuration

Enable Wake On LAN in Linux

• Enable Wake On LAN in BIOS

• Get current config: nmcli connection show "Wired connection 1" | grep 80

  • search for: 802-3-ethernet.wake-on-lan: default

• Set default setting to magic to enable wake on lan: sudo nmcli connection modify "Wired connection 1" 802-3-ethernet.wake-on-lan magic

• Disable wake on lan: sudo nmcli connection modify "Wired connection 1" 802-3-ethernet.wake-on-lan disabled

• Check if WOL magic packet is received: sudo nc -u -l -p 9

• To send magic packet from a linux machine: use wakeonlan $macaddress or etherwake $macaddress

Configure Network

Check network interface

• ip -4 -br a: View IPv4 address of all interfaces in brief format

• conntrack -L: show connection tables

• sipcalc 192.168.1.0/24: calculate ip addresses

Configure routing

• Routing configuration file: /etc/iproutes/rt_tables

• ip route add default via 192.168.1.1 table wan1: add default gateway for routing table wan1 (like vrf)

• ip route add 1.1.1.1 via 192.168.1.1 metric 100

• sysctl net.ipv4.fib_multipath_hash_policy: get multipath settings

• sysctl -w net.ipv4.fib_multipath_hash_policy=1: enable multipath

• ip route add 1.1.1.1 nexthop via 192.168.1.1 nexthop via 192.168.2.1: set route for multipath

• ip route add unreachable 2.2.2.2: set null0 route, source receives Host unreachable icmp

• ip route add prohibit 3.3.3.3: set null0 route, source receives packet filtered icmp

• ip route add blackhole: set null0 route, packet is silently dropped. This route is used in BGP to advertise route not in routing table

Policy-based routing

• ip rule: check routing rule, lower rule is checked first

• ip rule add from 10.0.0.0/24 table wan1

• ip rule add from 20.0.0.0/24 table wan2

• ip rule add fwmark 100 table wan1: route traffic based on firewall mark 100

• ip rule add fwmark 200 table wan2: route traffic based on firewall mark 200

• ip rule add lookup main suppress_prefixlength 0: lookup routing table main for all route except for route to /0 (default route)

Check Routing table

• ip route get 8.8.8.8 [fibmatch]: get ip route to 8.8.8.8

• ip route get 8.8.8.8 from 10.1.1.1 fibmatch: check policy-based routing

• ip route show scope host table all

• ip route show scope link table all

• ip route show global

• ip route show [table local | main]

Configuring Network using Network Manager

• systemctl restart NetworkManager: restart Network Manager

Enable Vlan

• sudo apt update

• sudo apt install vlan: for Ubuntu/Debian

  • sudo yum install vconfig: for RHEL/CentOS

• sudo modprobe 8021q: enable VLAN support in the kernel

  • echo "8021q" | sudo tee -a /etc/modules: make it persistent

Create VLAN configuration

nmcli con add type vlan con-name vlan2 ifname enp86s0.2 dev enp86s0 id 2 ipv4.method auto
nmcli con add type vlan con-name vlan4 ifname enp86s0.4 dev enp86s0 id 4 ipv4.method manual ipv4.addresses "192.168.4.100/24"
nmcli con up vlan2
nmcli con up vlan4

# Modify ip address
nmcli con modify vlan4 ipv4.addresses "192.168.4.199/24"

Change Interface Address from dhcp to manual

nmcli con modify "Wired connection 1" ipv4.method manual ipv4.addresses "192.168.1.100/24" ipv4.gateway "192.168.1.1"
nmcli con up "Wired connection 1"

Change Interface Address from manual to dhcp

nmcli con modify vlan6 ipv4.method auto

Change interface name to eth0

nmcli con modify "Wired connection 1" connection.id eth0
nmcli con up eth0

Disable Ip Address on interface (no DHCP or manual address)

nmcli con modify "Wired connection 1" ipv4.method disabled
nmcli con up "Wired connection 1"

Verification

• nmcli con show

• ip addr show enp86s0.2

• ip addr show enp86s0.4

• check configuration files in /etc/NetworkManager/system-connections/

Configure Network using ip command

sudo ip link add link eth0 name eth0.100 type vlan id 100
sudo ip addr add 192.168.100.1/24 dev eth0.100
sudo ip link set eth0.100 up

View ARP Table

• arp -a

• ip neigh show

  • ip -s neigh show: view with details

• cat /proc/net/arp

Reference

• Enable Wake-on-LAN to Wake up (or Boot) Ubuntu 24.04 Remotely

• How To Wake Up Computers Using Linux Command [ Wake-on-LAN ( WOL ) ] By Sending Magic Packets

• Linux IP Routing Basics: Routes, Tables, and Policy-based routin

• Network Namespaces