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Show information about connections

lsof

lsof -i -P -n -sTCP:LISTEN
  • i select IPv[46] files.
  • P no port names.
  • n no host names.
  • sTCP:LISTEN select protocol and state(s) by name.

ss

ss -n -A inet -E -H
  • n don't resolve service names
  • r resolve host names
  • t display only TCP sockets
  • a display all sockets
  • u display only UDP sockets
  • l display listening sockets
  • p show process using socket
  • i show internal TCP information
  • E continually display sockets as they are destroyed
  • 4 display only IP version 4 sockets
  • K forcibly close sockets, display what was closed
  • H Suppress header line
  • O socket's data printed on a single line
  • A QUERY. Some queries are inet, tcp
  • F Filter. Some filters are established, syn-sent, time-wait, listening

netstat

sudo netstat -tulnp
  • t show TCP ports.
  • u show UDP ports.
  • l show only listening ports.
  • n show numerical addresses instead of resolving hosts.
  • p show the PID and name of the listener’s process. This information is shown only if you run the command as root or sudo user.

Capture traffic

TLDR of tcpdump

Set up a network configuration

You need IP, Mask, Gateway, Route and DNS.

ifupdown

man interfaces

/etc/network/interfaces
---
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static

allow-hotplug eth1
iface eth1 inet static
    address 192.168.11.100/24
    gateway 192.168.11.1
    dns-domain example.com
    dns-nameservers 192.168.11.1 9.9.9.9
    pre-up echo "nameserver 192.168.11.1\nnameserver 9.9.9.9" > /etc/resolv.conf

## Subinterface
auto eth1:1
iface eth1:1 inet static
    address 192.168.11.101/24

## Vlan
allow-hotplug eth2 eth2.10
iface eth2 inet static
    address 10.0.0.23/24
    gateway 10.0.0.1
    scope link
    up ifup eth2.10

iface eth2.10 inet dhcp
    hostname server.example.com
    metric 100
    scope host

/etc/resolv.conf
---
nameserver 192.168.11.1
domain example.com

NetworkManager

Show connections

nmcli connection show

Disconnect

nmcli connection down enp3s0

Connect

nmcli connection up wlp3s0

Add a new connection

nmcli connection add type ethernet con-name Work ifname enp0s3
nmcli con -a con-name Home ## Will ask for any missing parameters

Delete a connection

nmcli con delete enp3s0.50

Change the name of a connection

nmcli con mod enp3s0 con-name Home

Details of a connection

nmcli con show enp3s0

Static connection

nmcli con add con-name static ifname enp3s0 ip4 192.168.1.50/24 gw4 192.168.1.1
nmcli con add con-name static ifname enp3s0 ipv4.method manual ip4 192.168.1.50/24 gw4 192.168.1.1 ipv4.dns "8.8.8.8 1.1.1.1" connection.autoconnect no connection.permissions user:user,yu

Add a route

nmcli c mod eth0 ipv4.routes "0.0.0.0/0 192.168.0.1"

Bridge for vlan. (use vlans in QEMU)

nmcli connection add type bridge con-name Bridge0 ifname br0 ip4 192.168.0.2/24
nmcli connection add type vlan con-name V20 ifname enp3s0.20 dev enp3s0 id 20 master br0 slave-type bridge

## Firewall
sudo iptables -A FORWARD -p udp -i br0 -o br0 --sport 67:68 --dport 67:68 -j ACCEPT
sudo iptables -A FORWARD -p icmp -i br0 -o br0 -j ACCEPT

Wifi

Scan networks.

nmcli device wifi list

Connect to network

nmcli --ask device wifi connect "myssid"

iproute2

Show connections

ip link
ip l
ip link show eno1
ip -brief link

ip address
ip a
ip a s eno1
ip -brief address

Show routes

ip route

Show neighbors (ARP)

ip neighbour
ip neigh show

Add an IP address

ip addr add <ip/mask> dev <interface>
ip addr add 192.168.0.123/28 dev eno1

Add a route

ip route add <network> via <ip> dev <interface>
ip route add 172.16.34.0/23 via <ip> dev <interface>

Add a default route

ip route add default via <ip> dev <interface>
ip route add default via 192.168.0.1 dev eno1

Set an interface up/down

ip link set <interface> <up/down>
ip link set eno1 up

Remove an IP address

ip addr del <ip/mask> dev <interface> metric <metric>
ip addr del 192.168.0.123/28 dev eno1

Remove a route

ip route del default via <ip> dev <interface>
ip route del default via 192.168.0.1 dev eno1

netplan

The directory should be at /etc/netplan.

Apply the configuration

netplan generate
netplan --debug apply

Example:

network:
  ethernets:
    enp1s0:
      addresses:
      - 192.168.0.59/24
      gateway4: 192.168.0.1
      nameservers:
        addresses:
        - 8.8.8.8
        - 1.1.1.1
        search: []
  version: 2

Bridge:

network:
    ethernets:
      enp1s0:
        dhcp4: false
        dhcp6: false

    bridges:
      br0:
        interfaces: [enp1s0]
        addresses: [192.168.0.59/24]
        gateway4: 192.168.0.1
        nameservers:
          addresses: [8.8.8.8,1.1.1.1]
        dhcp4: false
        dhcp6: false
        parameters:
          forward-delay: 0

    version: 2

systemd-networkd

man systemd-networ

Basic network with manual configuration:

/etc/systemd/network/eth0.network
---
[Match]
Name=eth0

[Network]
Address=192.168.122.45/24
Gateway=192.168.122.1
DNS=1.1.1.1

Basic network with mixed configuration:

/etc/systemd/network/enp1s0.network
---
[Match]
Name=enp1s0

[Network]
DHCP=yes

[DHCPv4]
RouteMetric=10

Restart the service to apply the changes:

systemctl restart systemd-networkd

Other parameters

Hostname

sudo hostnamectl set-hostname computer.domain.local

Timezone

sudo timedatectl set-timezone Europe/Paris

VLANs

Manual vlan

sudo ip link add link enp3s0 name enp3s0.20 type vlan id 20
sudo ip addr add 192.168.0.2/24 brd 192.168.0.255 dev enp3s0.20
sudo ip link set dev enp3s0.20 up

Remove.

sudo ip link set dev enp3s0.20 down
sudo ip link delete enp3s0.20

VLAN with NetworkManager

nmcli con add con-name enp3s0.50 type vlan vlan.id 50 vlan.parent enp3s0 ipv4.method manual ipv4.addresses 10.0.0.5/24 ipv4.gateway 10.0.0.1 connection.autoconnect no

VLANs with systemctl

/etc/systemd/network/eno1.network

[Match]
Name=eno1

[Network]
VLAN=eno1.10
VLAN=eno1.11
DNS=192.168.100.101
DNS=192.168.100.102

/etc/systemd/network/eno1.10.netdev

[NetDev]
Name=eno1.10
Kind=vlan

[VLAN]
Id=10

/etc/systemd/network/eno1.10.network

[Match]
Name=eno1.10

[Network]
Address=192.168.1.14/24
Address=192.168.1.24/24

[Route]
Gateway=192.168.1.1
Table=10

[RoutingPolicyRule]
From=192.168.1.0/24
Table=10

/etc/systemd/network/eno1.11.netdev

[NetDev]
Name=eno1.11
Kind=vlan

[VLAN]
Id=11

/etc/systemd/network/eno1.11.network

[Match]
Name=eth0.11

[Network]
Address=192.168.100.54/24

[Route]
Gateway=192.168.100.1
Table=11

[RoutingPolicyRule]
From=192.168.100.0/24
Table=11

Rename network adapter with udev rules

Find the MAC address 00:00:00:00:00:44

ip l
3: enp5s0f3u1u2u1: [...]
    link/ether 00:00:00:00:00:44 [...]

Ad a udev rule

/etc/udev/rules.d/70-net.rules
---
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:00:00:00:00:44", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="enpusb0"

You can also add the driver

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="ax88179_178a", ATTR{address}=="00:00:00:00:00:44", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="enpusb0"

Check the result. There is no need to reboot if you can unplug it.

4: enpusb0: [...]
    link/ether 00:00:00:00:00:44 [...]
    altname enp5s0f3u1u2u1

Rename network adapter with systemd-networkd

/etc/systemd/network/10-ethusb0.link
---
[Match]
MACAddress=12:34:56:78:90:ab

[Link]
Description=USB to Ethernet Adapter
Name=ethusb0

Sources