LECTION 1: NETWORKING

• Setting/changing an IP address
  There are several ways to set an IP address in Ubuntu:
  

  • CLI:
    

            sudo ifconfig eth0 192.168.0.110 netmask 255.255.255.0
    

    to add a default gateway:

            sudo route add default gw 192.168.0.1 eth0
    

  • GUI: I do not it that way!
    

  • /etc/network/interfaces
    In /etc/network/interfaces the basic configuration of interfeces is stored To obtain IP address dynamically, edit the file adding the following:
    

                    auto eth1 iface eth1 inet dhcp
    

    save the file and restart networking services using the below command:
    

                sudo systemctl restart networking
    

    To set IP address staticly, add the below lines to the file:
    

            auto eth1
            iface eth1 inet static address 192.168.0.111
    

• Setting up/ changing hostname
  The hostname of Ubuntu is configures in the file /etc/hostname

          sudo vim /etc/hostname
  

  The following is useful when I do not want to remember the IP addres, instead of that, I can map the hostname to IP address editing the /etc/hosts file.

          sudo vim /etc/hosts
          192.160.0.120 myOwnHostName
  

  save and reboot the system to apply changes.

• Enable or disable an specific interface.
  The ifup command allows enable an specific interface, for example:

          sudo ifup eth0
  

  The ifdown command allows disable an specific interface, for example:

          sudo ifdown eth0
  

• Ping command
  Packet INternet Groper is the best way to test connectivity between two nodes, PING uses ICMP (Internet Control Message Protocol) to communicate to other devices.

• Traceroute
  It is a network troubleshoot utility which shows number of hops taken to reach destination and also determine packet traveling path

          traceroute 8.8.8.8
          traceroute epa.com
  

• Netstat (Network statistic)
  It displays routing table and connection information, to display the routing table information is useful to use the option -r:

          netstat -r
  

• Dig (domain information groper)
  Dig query DNS related information like A Record, CNAME, MX Record etc. This command mainly use to troubleshoot DNS related query.
• nslookup
  This command also use to find out DNS related query
• route
  Route command also shows and manipulate ip routing table.
• host
  It is a command to find name to IP or IP to name in IPv4 or IPv6 and also query DNS records.
• (cURL) curl
  It is a command-line tool for getting or sending data including files using URL syntax. Since cURL uses libcurl, it supports every protocol libcurl supports
• wget: GNU Wget is a free utility for non-interactive download of files from the Web.
  It supports HTTP, HTTPS, and FTP protocols, as well as retrieval through HTTP proxies. Wget is non-interactive, meaning that it can work in the background, while the user is not logged on. This allows you to start a retrieval and disconnect from the system, letting Wget finish the work. By contrast, most of the Web browsers require constant user’s presence, which can be a great hindrance when transferring a lot of data. if while the downloading lost the connection, when restart the download not start from zero but start from it losted the connection
• Nmap
  nmap is a free and open source utility for network discovery and security auditing. It is useful to see which host are running in our networking
• tcpdump
  It is a command line utility that allows me to capture and analyze network traffic going through my system. It is often used to help troubleshoot network issues, as well as a security tool.
• TELNET & RLOGIN These are not good for communicating in networking because it sends passwords in plain text and we could use tcpdump or wireshark to capture these passwords.

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