Linux: What is Firewall? How it Works

Linux: What is Firewall? How it Works: "Firewall is a system that is present between external network i.e. Internet and internal network LAN. It allows your internal network to ..."

What is Firewall? How it Works

Firewall is a system that is present between external network i.e. Internet and internal network LAN. It allows your internal network to access the internet but it restrict external network so that not one access you LAN systems or data on your internal network. Firewall can also be defined as a device configured to allow and reject traffic on the basis of defined rules.

How it Works
Firewall stops all incoming traffic to internal IP addresses. Let us take an example of ping to understand the working of firewall. Whenever a ping command is executed it sends in ICMP echo request messages to source and in return receives ICMP echo reply. To block these ICMP echo request messages to reach destination we will configure firewall to fail the ping commands. Similarly SMTP protocol that response to TCP port 25 is used for email, blocking the port will disable the user in network to send emails.

Linux: How to Ping machine using hostname in debian/Linux...

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Linux: How to Ping machine using hostname in debian/Linux...: "We can ping machine by their hostname rather IP address gedit /hostname add hostname along with their IP addresses i.e 192.168.10.200..."

What is Rsync Utility

It is a backup/mirroring tools used to replicate between two locations on separate hosts in a network. In rsync only actual changed pieces of files are transferred rather than whole file, further saving your file transfer time and reducing load on network.

How to Ping machine using hostname in debian/Linux.

We can ping machine by their hostname rather IP address 

gedit  /hostname

add hostname along with their IP addresses
i.e 192.168.10.200 hostname
In this way you can  ping LAN systems with hostname

How to view TCP or UDP ports open or close at debian/Linux server

netstar -an
This will list all TCP and UDP ports

How to view Kernel IP routing table in debian/Linux

Every kernel makes its own routing table
command 
#  route