A firewall monitors incoming and outgoing network traffic and filters packets based on rules. A Linux firewall uses iptables to define rules for inbound and outbound traffic. Rules can allow or deny traffic by source, destination, and protocol. Network address translation (NAT) with iptables performs IP masquerading to hide private IP addresses and enable outbound internet access.

1. LINUX
FIREWALL
SHAR THU
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2. WHAT IS FIREWALL?
• Firewall is anything, hardware or software, that
monitors transmission of packets of digital information
that attempt to pass the perimeter of a network.
• Firewalls perform two basic security functions:
• (Network Traffics) Packet filtering
• Application proxy
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3. 3
FIREWALL SECURITY FEATURES
Some firewall manufacturers add features like:
 Logging unauthorized accesses into/out of a network
 Providing VPN link to another network
 Authenticating users
 Shielding hosts inside the network from hackers
 Caching data
 Filtering content considered inappropriate or dangerous

4. 4
FIREWALL COMPONENTS
• Packet filter
• Proxy server
• Authentication system
• Software that performs Network Address
Translation (NAT)
• Some firewalls:
• Can encrypt traffic
• Help establish VPNs
• Come packaged in a hardware device that also
functions as a router
• Make use of a bastion host

5. TYPES OF FIREWALL
• Client Firewall
• Windows firewall
• For a computer
• Network firewall
• Between private network & public network
• VPN, Routing, . . . .
• For each network by its rules
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6. NETWORK TRAFFIC
• Inbound traffic
• Outbound traffic
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Source Destination
(Requester) (Replier)
Ping 192.168.0.1 ICMP
Outbound Inbound
My Service (My internal network or my PC
His service

7. FILTER NETWORK TRAFFIC
• ACL (Access Control List)
• Allow (accept)
• Deny (drop or reject)
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8. FIREWALL RULES (OR) POLICIES
• Rule Name
• Action (allowed or deny)
• Traffic (inbound or outbound protocols)
• Source
• Destination
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source destination Traffic Action
1.1.1.1 192.1.1.1 ICMP Allow
Default Rule in Network Firewall >> All Traffic Deny (last priority)

9. NETWORK FIREWALL
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WHERE DOES USE A NETWORK FIREWALL?
Public
Private
Private
Private
BETWEEN PRIVATE & PUBLIC NETWORK!

10. NETWORK FIREWALL
• Front End
• Back End
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Internet
LAN
SW SW
LAN
SVR
ROOM
Private
DMZ
Front EndBack End

11. FIREWALLS
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SOHO FIREWALL DEVICES

12. FIREWALLS
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NETWORK FIREWALL DEVICES

13. LINUX FIREWALL
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14. LINUX IPTABLES FIREWALL
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Client Firewall (iptables)
#iptables –L INPUT (for input chain type or Inbound)
#iptables –L OUTPUT (for output chain type or outbound)
List

15. LINUX IPTABLES FIREWALL
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# iptables –A INPUT –s 192.168.0.1 –d 192.168.0.254 –p ICMP –j DROP
# iptables –A INPUT –s 192.168.0.0/24 –d 192.168.0.254/32 –p ICMP –j DROP
# iptables –L INPUT
# service iptables save
# service iptables start
Append INBOUND Rules in iptables ( Client Firewall )
Append Source Destination Protocol Jump
# iptables –D INPUT 1
Delete Line Number

16. LINUX IPTABLES FIREWALL
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# iptables –A INPUT –s 192.168.0.1 –d 192.168.0.254 –p TCP --sport xxx --dport 22 –j DROP
# iptables –A INPUT –s 192.168.0.1 –d 192.168.0.254 –p TCP --dport 443 –j ACCEPT
# iptables –A INPUT –s 0.0.0.0/0 –d 192.168.0.254 –p ICMP –j DROP
# iptables –A OUTPUT –s 192.168.0.254 –d 192.168.0.1 –p ICMP –j DROP
Append INBOUND Rules in iptables ( Client Firewall )
# iptables –D OUTPUT 1

17. PRIORITY OF FIREWALL RULE
Rule Name Action
Rule 1 ACCEPT
Rule 2 ACCEPT
Rule 3 ACCEPT
Rule 4 DROP
All Traffic Deny
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18. NAT WITH IPTABLE
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• Post Routing
• snat
• Pre Routing
• dnat
• Masquerade (Port Address Translation (PAT))
• Port Address Table
• IP Translation

19. NAT WITH IPTABLE
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• Masquerade (Port Address Translation (PAT))
1.1.1.1 10000
NAT
(PAT)
1.1.1.1 10000 20000
203.203.203.203 20000

20. NAT WITH IPTABLE
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• IP Translation
1.1.1.1 10000
NAT
(PAT)
1.1.1.1 10000
203.203.203.203 10000
Requester

21. NAT WITH IPTABLES
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Internet
Web
:80
SW
IP= 200.200.200.1
GW=200.200.200.254
IP= 192.168.0.254
IP= 192.168.0.1
GW=192.168.0.254
IP= 192.168.0.100
GW=192.168.0.254

22. SNAT (POSTROUTING) WITH IPTABLES
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Stap 1
Open Routing Function
Stap 2
Set Static IP (LAN/WAN)

23. SNAT (POSTROUTING) WITH IPTABLES
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One to One
# iptables -t nat -A POSTROUTING -s 192.168.1.2(LAN) -j SNAT --to 200.200.200.1(WAN-Public IP)
Many to One
# iptables -t nat -A POSTROUTING -s 192.168.1.0/24 -j SNAT --to 200.200.200.1
Many to Many
# iptables -t nat -A POSTROUTING -s 192.168.1.0/255.255.255.0 -j SNAT --to 200.200.200.1-200.200.200.6
Many to One(PAT)
# iptables -t nat -A POSTROUTING -s 192.168.1.0/255.255.255.0 -o eth0(WAN) -j MASQUERADE
# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
Port (1 to 65535)
# iptables –t nat –L
# iptables –t nat –L POSTROUTING
# iptables –t nat –F

24. DNAT (PREROUTING) WITH IPTABLES
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Port Forwarding

25. THANKS!!
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