2 Introduction of Firewall in Computer Network

Question 1

What is a firewall?

Answer 1

• HW or SW network security device
• barrier between secured internal network and outside network (eg - Internet)
• monitors all incoming and outgoing traffic

Question 2

What are 3 firewall security rules?

Answer 2

• Accept - allow the traffic
• Reject - block the traffic but reply with an “unreachable error”
• Drop - block the traffic with no reply

Question 3

How firewall works? (traffic and rules)

Answer 3

• network traffic has to be matched with defined rule

- when is matched –> associated action is applied to traffic

Question 4

Allowed or not? (outgoing and incoming traffic)

Answer 4

outgoing - allowed in most cases (good to have some rules to prevent unwanted communication)
incoming - tougher rules (this traffic is usually TCP, UDP, ICMP)

Question 5

What does firewall has to have set?

Answer 5

• default policy (A, J, D)

Question 6

How do packet filtering firewalls work?

Where are captured the rules?

Answer 6

• they control network access based on source add, destination add, port and protocols (monitoring of outgoing and incoming packets)
• rules are table (what is deny or allow)
• the packets are treat in isolation (no as a part of stream)

Question 7

How do Stateful Inspection Firewalls work?

Answer 7

• keep track of connection state of the packet

- decision are based on defined rules and on the packet´s history in the state table

Question 8

How do Application Layer Firewall work?

Answer 8

• ca inspect and filter packets on any OSI layer

- ability to block specific content

Question 9

What are and what do hosts that run proxy servers?

Answer 9

• application layer firewalls
• proxy firewall prevents direct connection between either side of the firewall - each packet has to pass through the proxy (allow or block –> predefined rules)
• can be used as NAT

Question 10

Next Gen Firewalls

Answer 10

• trying to stop modern security breaches (malware attacks, …)

Question 11

Host-based Firewalls

• where installed and what control
• SW or HW
• why needed

Answer 11

• installed on each network node (controls incoming and outgoing packets)
• SW - part of OS
• needed ‘cause network firewalls cannot provide protection inside a trusted network
• protect from attacks and unauthorized access

Question 12

Network-based Firewalls

• what protect
• SW or HW

Answer 12

• network level
• filter all incoming and outgoing traffic across the network
• protects internal network
• 2 or more NIC
• dedicated system with proprietary SW installed