4 How to Setup Firewall in Linux

Question 1

What is the default tool for setting a firewall?

Answer 1

iptables - set up, maintain packets filter (in linux kernel)

Question 2

What are chains?

Answer 2

• set of rules for particular task (3 for process the traffic)

Question 3

INPUT chains

Answer 3

• any traffic from internet towards your local machine has to go through all the rules in INPUT chain

Question 4

OUTPUT chains

Answer 4

• any traffic going from your local machine has to go through the output chains

Question 5

FORWARD chains

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Answer 5

• any traffic going from external network to another network needs to go through FORWARD chains (when two or more PCs are connected and we want to send data between them)

Question 6

What 3 actions does iptable perform on the traffic? (tell about each)

Answer 6

ACCEPT
- any traffic going from your local machine has to go through the output chains
DROP
- traffic is unable to pass the rules in specified chain → iptable blocks the traffic
- firewall is closed
REJECT
- similar to DROP
- it send a message to the sender of the traffic stating the data transfer has failed

Question 7

When to use REJECT and when DROP?

Answer 7

• use REJECT - you want to other end to know the port is unreachable
• use DROP - for connections to hosts you do not want people to see