E firewalls

29 December 2008 abhiroop@cdac 1

Firewalls

The function of a strong position is to make the forces holding it practically unassailable

-On War,(Carl Von Clausewitz)

ABHIROOP GHATAKen no: 0771184406


What is a Firewall?

A firewall is hardware, software, or a combination of both that is used to prevent unauthorized programs or Internet users from accessing a private network and/or a single computer.

A firewall is simply a program or h/w device that filters the info.coming through the internet connection into your private network or comp-system.IF an incoming packet of info.is flagged by the filters,it is not allowed through.


Hardware vs. Software Firewalls

Hardware Firewalls

Protect an entire network

Implemented on the router level

Usually more expensive, harder to configure

Software Firewalls

Protect a single computer

Usually less expensive, easier to configure


How does a software firewall work?

Inspects each individual “packet” of data as it arrives at either side of the firewall

Inbound to or outbound from your computer

Determines whether it should be allowed to pass through or if it should be blocked


Protected Private Network

Internet

Firewalls denies or permits access based on rules and policies


Firewall Rules

Allow – traffic that flows automatically because it has been deemed as “safe” (Ex. Meeting Maker, Eudora, etc.)

Block – traffic that is blocked because it has been deemed dangerous to your computer

Ask – asks the user whether or not the traffic is allowed to pass through


What a personal firewall can do

Stop hackers from accessing your computer

Protects your personal information

Allow virtual private networks

locks “pop up” ads and certain cookies

Determines which programs can access the Internet


Firewalls DON’T

Protect against attacks that bypass the firewall

Dial-out from internal host to an ISP

Protect against internal threats

disgruntled employee

Insider cooperates with and external attacker

Protect against the transfer of virus-infected programs or files


Type is Firewalls ..

Firewalls fall into four broad categories .

Packet filters

Application level

Circuit level

Stateful inspection firewalls


Packet filtering firewall


Packet Filtering Routers

• Forward or discard IP packet according a set of rules

• Filtering rules are based on fields in the IP and transport header

Presenter

Presentation Notes

A packet-filtering router makes a permit/deny decision for each packet that it receives. The router examines each datagram to determine whether it matches one of its packet-filtering rules. The filtering rules are based on the packet header information that is made available to the IP forwarding process. This information consists of the IP source address, the IP destination address, the encapsulated protocol (TCP, UDP, ICMP, or IP Tunnel), the TCP/UDP source port, the TCP/UDP destination port, the ICMP message type, the incoming interface of the packet, and the outgoing interface of the packet. If a match is found and the rule permits the packet, the packet is forwarded according to the information in the routing table. If a match is found and the rule denies the packet, the packet is discarded. If there is no matching rule, a user-configurable default parameter determines whether the packet is forwarded or discarded.


Packet-filter firewall


Application level gateway

Proxy serverFirewall

Data Link

Network

InternetPhysical

Data Link

NetworkInternalNetwork

Physical

Router

Transport

Application

Transport

Application

Application Proxies


Continue …

Act as relay of application-level traffic.The user contacts the gateway using TCP/IP application,such as FTP ,and the gateway asks the user for the name of a remote host to be accessed.When the user responds and provides a valid user ID and authentication info. the gateway contacts the application on the remote host and relays TCP segments containing the application data between the two points.


Proxy firewall


Circuit level gateway(Firewall)

Circuit level gateways work at the session layer of the OSI model.They monitor TCP handshaking between packets to determine whether a requested session is legitimate. Information passed to a remote computer through a circuit level gateway appears to have originated from the gateway. This is useful for hiding information about protected networks. Circuit level gateways are relatively inexpensive and have the advantage of hiding information about the private network they protect. On the other hand, they do not filter individual packets.


Circuit level gateway


Continue ..

Whether a connection is valid may for examples be based upon:

destination IP address and/or port

source IP address and/or port

time of day

protocol

user

password

Every session of data exchange is validated and monitored and all traffic is disallowed unless a session is open.


Stateful

inspection firewalls

Firewall/Router

Router

Network - Access Rules

Transport - Access Rules

Application - State Table

Inspection Module

Data Link

Network

Data Link

Network

InternalNetwork

PhysicalInternet

Physical


How to trust firewalls?

Firewalls can be trusted if they provide the following services

1)Authentication 2)access control 3)data confidentiality 4)data integrity 5)non repudiation


uses of firewalls

Virtual private network

Demiltarised zone

A DMZ can be viewed as a layer of privacy between the corporate infrastructure and the Internet, exposing only those systems that

must be known to the public.

Ip security


VPN


De-militarised

zone

Protected private network

Demilitarised Zone

MailServer

WEBServer

Internet

DMZ

Open accessbetween

private LANand DMZ

Static filtersbetween private LAN

and DMZ used to control access

Allow SMTP,

From hereto there

only


Ip security

Firewalls are needed when any organization relies heavily on the internet.


conclusion

Firewall must continue to advance

Firewalls must be developed to scan virus

$377 million (approx.) lost till datedue to network attacks

.



For additional information visit

http://www.pchelp.org/www.nwinternet.com/pchelp/security /firewalls.htm

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