A TECHNICAL PAPER PRESENTATION

NETWORK SECURITY

Abstract

Network security can be described as the effort to create a secure computing platform, designed so that agents (users or programs) cannot perform actions that they are not allowed to perform, but can perform the actions that they are allowed to. Network Security systems insure the integrity of the system by protecting from hackers trying to get into the system and by restricting access within the system to individuals specific needs.

We have dealt with one of the Basic Network Security Tools the Firewalls. It is a combination of hardware and software that secures access to a local network or computer. A firewall guards the local network by analyzing the data leaving and entering, allowing authorized traffic through while keeping unauthorized traffic out.

Firewalls are typically configurable by network administrators so that they can set policy to determine what traffic is deemed safe. A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system. Firewalls use one or more of three methods to control traffic flowing in and out of the network: packet filtering, proxy service, and stateful inspection.

Firewalls are customizable (add or remove filters) through IP address, protocols, domain services etc. They protect the network from SMTP session hijacking, denial of service, spam, viruses, e-mail bombs etc. A function that is often combined with a firewall is a proxy server. The proxy server is used to access Web pages by the other computers.

Hence we conclude that Network Security has become a mandatory thing for every network to such an extent that we can’t imagine a world without it in future.

Contents

· Introduction

· What is Network Security?

· What is a Firewall?

· How Firewalls Work?

· What It Does

· Making the Firewall Fit

· What It Protects You From

· Proxy Servers and DMZ

· Conclusions

Introduction

Network is medium for communication. Security has become a mandatory thing for every network .To protect these networks from attacks (that may be internal or external) security must be provided. It can be provided through secure network devices like firewalls.

What is Network Security?

We have dealt with one of the Basic Network Security Tools the Firewalls.

What is a Firewall?

A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranet. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.

Firewalls make it possible to filter incoming and outgoing traffic that flows through your system. A firewall can use one or more sets of ``rules'' to inspect the network packets as they come in or go out of your network connections and either allows the traffic through or blocks it. The rules of a firewall can inspect one or more characteristics of the packets, including but not limited to the protocol type, the source or destination host address, and the source or destination port.

Firewalls can greatly enhance the security of a host or a network. They can be used to do one or more of the following things:

· To protect and insulate the applications, services and machines of your internal network from unwanted traffic coming in from the public Internet.

· To limit or disable access from hosts of the internal network to services of the public Internet.

· To support network address translation (NAT), which allows your internal network to use private IP addresses and share a single connection to the public Internet (either with a single IP address or by a shared pool of automatically assigned public addresses).

After reading this chapter, you will know:

· How to properly define packet-filtering rules.

· The differences between the firewalls built into FreeBSD.

· How to use and configure the OpenBSD PF firewall.

· How to use and configure IPFILTER.

· How to use and configure IPFW.

Before reading this chapter, you should:

· Understand basic FreeBSD and Internet concepts

How Firewalls Work?
Basically, a firewall is a barrier to keep destructive forces away from your property. In fact, that's why it’s called a firewall. Its job is similar to a physical firewall that keeps a fire from spreading from one area to the next.

What It Does

A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system. If the filters flag an incoming packet of information, it is not allowed through. For example let’s see how a firewall helps protect computers inside a large company. Let's say that you work at a company with 500 employees. The company will therefore have hundreds of computers that all have network cards connecting them together. In addition, the company will have one or more connections to the Internet through something like T1 or T3 lines. Without a firewall in place, all of those hundreds of computers are directly accessible to anyone on the Internet. A person who knows what he or she is doing can probe those computers, try to make FTP connections to them, try to make telnet connections to them and so on. If one employee makes a mistake and leaves a security hole, hackers can get to the machine and exploit the hole.

With a firewall in place, the landscape is much different. A company will place a firewall at every connection to the Internet (for example, at every T1 line coming into the company). The firewall can implement security rules. For example, one of the security rules inside the company might be:

Out of the 500 computers inside this company, only one of them is permitted to receive public FTP traffic. Allow FTP connections only to that one computer and prevent them on all others.

A company can set up rules like this for FTP servers, Web servers, Telnet servers and so on. In addition, the company can control how employees connect to Web sites, whether files are allowed to leave the company over the network and so on. A firewall gives a company tremendous control over how people use the network.

Firewalls use one or more of three methods to control traffic flowing in and out of the network:

· Packet filtering - Packets (small chunks of data) are analyzed against a set of filters. Packets that make it through the filters are sent to the requesting system and all others are discarded.

· Proxy service - Information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa.

· Stateful inspection - A newer method that doesn't examine the contents of each packet but instead compares certain key parts of the packet to a database of trusted information. Information traveling from inside the firewall to the outside is monitored for specific defining characteristics, and then incoming information is compared to these characteristics. If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded.

Making the Firewall Fit
Firewalls are customizable. This means that you can add or remove filters based on several conditions. Some of these are:

· IP addresses - Each machine on the Internet is assigned a unique address called an IP address. IP addresses are 32-bit numbers, normally expressed as four "octets" in a "dotted decimal number." A typical IP address looks like this: 216.27.61.137. For example, if a certain IP address outside the company is reading too many files from a server, the firewall can block all traffic to or from that IP address.

· Domain names - Because it is hard to remember the string of numbers that make up an IP address, and because IP addresses sometimes need to change, all servers on the Internet also have human-readable names, called domain names. For example, it is easier for most of us to remember www.howstuffworks.com than it is to remember 216.27.61.137. A company might block all access to certain domain names, or allow access only to specific domain names.

· Protocols- The protocol is the pre-defined way that someone who wants to use a service talks with that service. The "someone" could be a person, but more often it is a computer program like a Web browser. Protocols are often text, and simply describe how the client and server will have their conversation. The http in the Web's protocol. Some common protocols that you can set firewall filters for include:

· IP (Internet Protocol) - the main delivery system for information over the Internet

· TCP (Transmission Control Protocol) - used to break apart and rebuild information that travels over the Internet

· HTTP (Hyper Text Transfer Protocol) - used for Web pages

· FTP (File Transfer Protocol) - used to download and upload files

· UDP (User Datagram Protocol) - used for information that requires no response, such as streaming audio and video

· ICMP (Internet Control Message Protocol) - used by a router to exchange the information with other routers

· SMTP (Simple Mail Transport Protocol) - used to send text-based information (e-mail)

· SNMP (Simple Network Management Protocol) - used to collect system information from a remote computer

· Telnet - used to perform commands on a remote computer

A company might set up only one or two machines to handle a specific protocol and ban that protocol on all other machines.

· Ports- Any server machine makes its services available to the Internet using numbered ports, one for each service that is available on the server. For example, if a server machine is running a Web (HTTP) server and an FTP server, the Web server would typically be available on port 80, and the FTP server would be available on port 21. A company might block port 21 accesses on all machines but one inside the company.

· Specific words and phrases - This can be anything. The firewall will sniff (search through) each packet of information for an exact match of the text listed in the filter. For example, you could instruct the firewall to block any packet with the word "X-rated" in it. The key here is that it has to be an exact match. The "X-rated" filter would not catch "X rated" (no hyphen). But you can include as many words, phrases and variations of them as you need.

Some operating systems come with a firewall built in. Otherwise, a software firewall can be installed on the computer in your home that has an Internet connection. This computer is considered a gateway because it provides the only point of access between your home network and the Internet.

With a hardware firewall, the firewall unit itself is normally the gateway. A good example is the Linksys Cable/DSL router. It has a built-in Ethernet card and hub. Computers in your home network connect to the router, which in turn is connected to either a cable or DSL modem. You configure the router via a Web-based interface that you reach through the browser on your computer. You can then set any filters or additional information.

Hardware firewalls are incredibly secure and not very expensive. Home versions that include a router, firewall and Ethernet hub for broadband connections can be found for well under $100.

What It Protects You From
There are many creative ways that unscrupulous people use to access or abuse unprotected computers:

· Remote login - When someone is able to connect to your computer and control it in some form. This can range from being able to view or access your files to actually running programs on your computer.

· Application backdoors - Some programs have special features that allow for remote access. Others contain bugs that provide a backdoor, or hidden access, that provides some level of control of the program.

· SMTP session hijacking - SMTP is the most common method of sending e-mail over the Internet. By gaining access to a list of e-mail addresses, a person can send unsolicited junk e-mail (spam) to thousands of users. This is done quite often by redirecting the e-mail through the SMTP server of an unsuspecting host, making the actual sender of the spam difficult to trace.

· Operating system bugs - Like applications, some operating systems have backdoors. Others provide remote access with insufficient security controls or have bugs that an experienced hacker can take advantage of.

· Denial of service - You have probably heard this phrase used in news reports on the attacks on major Web sites. This type of attack is nearly impossible to counter. What happens is that the hacker sends a request to the server to connect to it. When the server responds with an acknowledgement and tries to establish a session, it cannot find the system that made the request. By inundating a server with these unanswerable session requests, a hacker causes the server to slow to a crawl or eventually crash.

· E-mail bombs - An e-mail bomb is usually a personal attack. Someone sends you the same e-mail hundreds or thousands of times until your e-mail system cannot accept any more messages.

· Macros - To simplify complicated procedures, many applications allow you to create a script of commands that the application can run. This script is known as a macro. Hackers have taken advantage of this to create their own macros that, depending on the application, can destroy your data or crash your computer.

· Viruses - Probably the most well known threat is computer viruses. A virus is a small program that can copy itself to other computers. This way it can spread quickly from one system to the next. Viruses range from harmless messages to erasing all of your data.

· Spam - Typically harmless but always annoying, spam is the electronic equivalent of junk mail. Spam can be dangerous though. Quite often it contains links to Web sites. Be careful of clicking on these because you may accidentally accept a cookie that provides a backdoor to your computer.

· Redirect bombs - Hackers can use ICMP to change (redirect) the path information takes by sending it to a different router. This is one of the ways that a denial of service attack is set up.

· Source routing - In most cases, the path a packet travels over the Internet (or any other network) is determined by the routers along that path. But the source providing the packet can arbitrarily specify the route that the packet should travel. Hackers sometimes take advantage of this to make information appear to come from a trusted source or even from inside the network! Most firewall products disable source routing by default.

Some of the items in the list above are hard, if not impossible, to filter using a firewall. While some firewalls offer virus protection, it is worth the investment to install anti-virus software on each computer. And, even though it is annoying, some spam is going to get through your firewall as long as you accept e-mail.

The level of security you establish will determine how many of these threats can be stopped by your firewall. The highest level of security would be to simply block everything. Obviously that defeats the purpose of having an Internet connection. But a common rule of thumb is to block everything, and then begin to select what types of traffic you will allow. You can also restrict traffic that travels through the firewall so that only certain types of information, such as e-mail, can get through. This is a good rule for businesses that have an experienced network administrator that understands what the needs are and knows exactly what traffic to allow through. For most of us, it is probably better to work with the defaults provided by the firewall developer unless there is a specific reason to change it.

One of the best things about a firewall from a security standpoint is that it stops anyone on the outside from logging onto a computer in your private network. While this is a big deal for businesses, most home networks will probably not be threatened in this manner. Still, putting a firewall in place provides some peace of mind.

Proxy Servers and DMZ

A function that is often combined with a firewall is a proxy server. The proxy server is used to access Web pages by the other computers. When another computer requests a Web page, it is retrieved by the proxy server and then sent to the requesting computer. The net effect of this action is that the remote computer hosting the Web page never comes into direct contact with anything on your home network, other than the proxy server.

Proxy servers can also make your Internet access work more efficiently. If you access a page on a Web site, it is cached (stored) on the proxy server. This means that the next time you go back to that page, it normally doesn't have to load again from the Web site. Instead it loads instantaneously from the proxy server.

There are times that you may want remote users to have access to items on your network. Some examples are:

· Web site

· Online business

· FTP download and upload area

In cases like this, you may want to create a DMZ (Demilitarized Zone). Although this sounds pretty serious, it really is just an area that is outside the firewall. Think of DMZ as the front yard of your house. It belongs to you and you may put some things there, but you would put anything valuable inside the house where it can be properly secured.

Setting up a DMZ is very easy. If you have multiple computers, you can choose to simply place one of the computers between the Internet connection and the firewall. Most of the software firewalls available will allow you to designate a directory on the gateway computer as a DMZ.

Conclusions

Everyone has a different idea of what “security” is, and what levels of risk are acceptable. The key for building a secure network is to define what security means to your organization. Once that has been defined, everything that goes on with the network can be evaluated with respect to that policy. Projects and systems can then be broken down into their components, and it becomes much simpler to decide whether what is proposed will conflict with your security policies and practices.

Many people pay great amounts of lip service to security, but do not want to be bothered with it when it gets in their way. It's important to build systems and networks in such a way that the user is not constantly reminded of the security system around him. Users who find security policies and systems too restrictive will find ways around them. It's important to get their feedback to understand what can be improved, and it's important to let them know why what have been done has been, the sorts of risks that are deemed unacceptable, and what has been done to minimize the organization's exposure to them.

Security is everybody's business, and only with everyone's cooperation, an intelligent policy, and consistent practices, will it be achievable.

Bibliography

Books

1. ‘Firewalls Clearly Explained’ by John R Vacca.

2. ‘The Definitive Guide To Firewalls’ by Northcutt, Stephen

Website

www.computer.howstuffworks.com/home-network.htm
www.grc.com

Paper presentation

Search This Blog

Tuesday 1 March 2011

NETWORK SECURITY