Networking

IP (Internet Protocol) requires hosts to be given IP addresses and then can route packets among them.

TCP (which stands for Transmission Control Protocol) setup a virtual circuit between two hosts. Data of arbitrary size can then be sent across this circuit using the segmentation and reassembling capabilities of TCP. Other Transport protocols include UDP and ICMP.

TCP/IP utilities

To fully understand how networking works in Linux, it is important to know the following commands: ping, traceroute, nslookup and dig, telnet and ftp and whois.

TCP/IP configuration and troubleshooting

In Linux, TCP/IP is configured either graphically or using the command line.

• Graphical NetworkManager
• Network Configuration Files
• Interface Configuration Files
• ifconfig and route

Maintaining security with TCP Wrappers

• TCP Wrappers allows the system administrator to manage access to specific services using /etc/hosts.allow and /etc/hosts.deny. The services which can be controlled using TCP Wrappers are linked to the tcp_wrappers-libs library.

Another way to maintain security is to use a Firewall to limit access to services.

OpenSSH

The OpenSSH server is a powerful service which provides the following capabilities:

• The ssh command
• The scp command
• The sftp command
• X11 forwarding
• Port forwarding
• Passwordless authentication using keys

In addition to that, ssh can also be configured by changing /etc/sshd/ssh_config and /etc/sshd/sshd_config. One important configuration is to disable root logins.