network-linux.md

Network on Linux

Setup static ip

Finding your network interfaces name

ip -c link show
ip addr

Show info

ip -c addr show enp0s5

Starting and Stopping Interfaces

ifdown enp7s0
ifup enp7s0

Force an Interface release & request new ip from DHCP server for specific interface

sudo dhclient -r <interface>
sudo dhclient <interface>

Modify /etc/network/interfaces

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto enp0s5
iface enp0s5 inet static
    address 192.168.0.20/24
    gateway 192.168.0.1

NOTE

• If setting multiple interfaces with static ip, gateway properties should be defined for 1 interface only
• If RTNETLINK answers: file exists error shown, try bellow command to clear assigned ip address

sudo ip addr flush <interface>

Restart network service

sudo systemctl restart networking.service

Setting DNS

To make it use the DHCPv4 protocol to obtain dns servers address

sudo dhclient -4

To manual config DNS, modify /etc/resolv.conf

nameserver 192.168.0.1
nameserver 8.8.8.8

NOTE: Make sure there is no interface with dhcp setting in /etc/network/interfaces, otherwise this file will be overwritten

Confirm DNS

ip route
nslookup google.com
traceroute google.com
dig google.com

Ref:

• https://wiki.debian.org/resolv.conf
• https://manpages.debian.org/bookworm/isc-dhcp-client/dhclient.8.en.html

Disable ipv6

Add the following at the bottom of the file /etc/sysctl.conf

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

Then run

sysctl -p

Ref:

• https://support.nordvpn.com/hc/en-us/articles/20164669224337-How-to-disable-IPv6-on-Linux

Manage route

Find current default gateway

ip route show 0.0.0.0/0

Manage route

ip route add {NETWORK} via {IP} dev {DEVICE}
sudo ip route add 89.187.160.1/32 via 192.168.1.1 dev enp6s16

Ref: https://www.cyberciti.biz/tips/configuring-static-routes-in-debian-or-red-hat-linux-systems.html/

Ping using specific NIC

ping google.com -I enp6s16

Test real network speed

Install iperf3

apt install iperf3

Find a iperf3 server address on google, then test speed by

iperf3 -c <iperf3 server>
iperf3 -c <iperf3 server><device>
iperf3 -c 89.187.160.1%enp6s16

Ref: https://iperf2.sourceforge.io/iperf-manpage.html

Trace route

Perform traceroute using specific internet interface

traceroute -i eth0 google.com

Trace route to a service (Windows)

tracert 8.8.8.8

Scan Local network

Scan all ip in local network

nmap -sn 192.168.0.*

Scan all ip and port

nmap 192.168.0.*

Flags have the following meanings:

• -vv (Increase verbosity)
• -n (No DNS resolution. This speeds up our scan!)
• -sn (No port scan)
• -PE (Use ICMP echo request queries. This is what is displayed in the output above)
• -T4 (prohibits the dynamic scan delay from exceeding 10 ms for TCP ports. See man nmap).
• --packet-trace (Trace sent and received packets)

To scan all hostname in local network use avahi

• Install

apt install avahi-daemon avahi-utils

• Run

avahi-browse -art

Check listing port

sudo lsof -i -P -n
less /etc/services

Test connection to a website by fetching web content from CLI

curl -L $url
wget -O - $url

Multicast DNS (mDNS)

To setup mDNS

sudo apt install avahi-daemon
sudo systemctl start avahi-daemon
sudo systemctl enable avahi-daemon

Then we can use <hostname>.local to access