Understanding Firewalls via an Analogy

1
Understanding Firewalls via an Analogy

• SRA 221
• College of IST

2
The confusing concepts

• A network receives packets and sends out packets
• What is a network?
• What is a packet?
• The attacker hacks a network via packets
• Why a packet can enable the attacker to break
  into the network?
• Firewalls can protect a network
• Why?

3
A network a military base
outside
outside
Mission Critical!
Money Critical!
Web server
C C building
Road
LAN
Order Processing Server
Weapon building
Solider building
Customer database
Network
Military base
4
A packet a van
outside
Packet
Packet
Mission Critical!
Money Critical!
Web server
C C building
Road
LAN
Order Processing Server
Weapon building
Solider building
Customer database
Network
Military base
5
Good packets vs. bad packets
A good packet a truck with chocolate
Useful data
A bad packet a truck with terrorists and bombs
Malicious code
6
A bad packet can hack the network if you let it
in!
Packet
Packet
Mission Critical!
Money Critical!
Web server
C C building
Road
LAN
Order Processing Server
Weapon building
Solider building
Customer database
Network
Military base
7
A network needs a firewall a military base
needs a guard
Packet
Packet
Checkpoint
Firewall
Web server
C C building
Road
LAN
Order Processing Server
Weapon building
Solider building
Customer database
Network
Military base
8
A packet filtering firewall a guard that only
checks the driver
Header
Driver
Payload
Payload
Useful data
So a packet filtering firewall only checks the
header
Which base are you from?
Source IP address
Source port number
Which unit are you from?
Dest IP address
Which base are you to?
Dest port number
Which unit are you to?


9
A proxy firewall a pseudo center
Packet
Telnet Proxy server
Pseudo C C center
Real CC center
Real Telnet Server
Network
Military base