Interface configuration files:

• /etc/nsswitch.conf → where resolve hostname to IP address

• /etc/hosts → add new IP to resolve

• /etc/resolv.conf → resolve hostname

• netstat → what’s happening on the network

• tcpdump -i networkinterface (wifi, wlp2s0)

  • network sniffing

NIC → network interface card

• lo → loopback (local machine)
• virbr0 → virtual bridge

ETHTOOL ENP0S3

• Speed? / Duplex?

• Link detected:

  • YES → network is working
  • NO → not working

NIC BONDING

• Combine 2 NIC (ethernet port)

  • For redundancy
  • High availability
  • Link aggregation → 1G + 1G = 2G

• modprobe bonding

1. Create a bond interface file:

   • nano /etc/sysconfig/network-scripts/ifcfg-bond0

2. Create first NIC file → ifcfg-enp0s3

   • Add MAC, IP, etc.
3. Create second NIC file → ifcfg-enp0s8
4. systemctl restart network

cat /proc/net/bonding/bond0 → show bond interface settings

Network utilities

• nmcli → network manager command line interface
• nmtui → network manager text user interface
• nm-connection-editor → GUI for most of the network manager
• nmtui → team (to create bond)

• nmcli device → listing of interface

• nmcli connection modify enp0s3 ipv4.addresses 192.168.0.180/24

• nmcli connection modify enp0s3 ipv4.gateway 192.168.0.1

• nmcli connection modify enp0s3 ipv4.method manual
  NMCLI

• nmcli connection down enp0s3

• nmcli connection up enp0s3

• ip address show enp0s3

Download File

• wget http://mydomain.com/soft.deb

Find Out Page (Website) is Up

• curl http://website.com/
• curl -O http://web.com/file → download a file
• ping → get IP response
• nslookup → info sur le site

SS

• Check how device talk to the internet

  • Identify problem

Socket

• Enable data transmission

  • TCP, UDP, UNIX

TCP (Transmission Control Protocol)

• Rule: data is sent successfully (HTTP, FTP, SMTP)

UDP (User Datagram Protocol)

• Sending data without checking if it arrives correctly
• Video streaming

UNIX

• Way for programs to talk to each other
• Use a special file for message exchange
• Database / webservers / local system

SS Options

• ss -t → show TCP connection
• ss -u → show UDP connection
• ss -x → show UNIX connection
• ss -l → listening sockets
• ss -n → display addresses in numerical form