1. Network Security – Part 1

1.1.        Security functions of network devices


Firewalls are security devices designed to control traffic and protect networks from each other they’re usually applied to protect high trust networks from low trust ones or to stop networks part of the same organisation but from different departments. They can be either hardware or software.

There are four different types of firewalls:

Packet filter Firewalls – uses the packet header to do basic traffic filtering usually based of the source and destination address, port numbers and protocols. They operate in the network and transport layers of the OSI model. Continue reading


Uses of free Unix-based Security Tools to Develope Secure Systems – Part 4


“Enumeration can best be defined as the process of counting. From a security standpoint, it’s the process the attacker follows before an attack. The attacker is attempting to count or identify systems and understand their role or purpose.

This may mean the identification of open ports, applications, vulnerable services, DNS or NetBIOS names, and IP addresses before an attack.”

Michael Gregg (2008, p 149)

This means at this stage it’s only a matter of time before the attacker compromises a system on the network.

The main aim of this stage is to find:

Uses of free Unix-based Security Tools to Develope Secure Systems – Part 3


At this stage an attacker would’ve got a list of IP ranges, DNS servers, Mail servers, employee names and phone numbers. All this would be used by attackers to probe our network to see which systems are alive and the services running on them.

There are many tools and techniques available to accomplish this.

Ping sweeps basically a method used to find out which of a range of IP addresses are a live and reachable from the internet.

Fping can be used on large networks, it doesn’t wait for a reply before trying the next IP, it sends many requests in parallel.

root@bt:#fping -a -f ipadd.txt

-a – shows systems that are alive.

-d – resolves hostnames.

-f – read from file.

-h – help.

Nmap is another tool that can be used for ping sweeps.

root@bt:#nmap –sP

There are other methods that can be used if ICMP is blocked but they are not as accurate as Continue reading

Uses of free Unix-based Security Tools to Develope Secure Systems – Part 2


The aim of foot printing is to gather as much information as possible about the organisation and its network. One would ask why would I need to perform such step when I have all the information about my network?

Joel Scambray, Stuart McClure and George Kurtz (2009, page 10), answers this question:

“Foot printing is necessary for one basic reason: it gives you a picture of what the hacker sees. And if you know what the hacker sees, you know what potential security exposures you have in your environment. And when you know what exposures you have, you know how to prevent exploitation.

Hackers are very good at one thing: getting inside your head, and you don’t even know it. They are systematic and methodical in gathering all pieces of information related to the technologies used in your environment. Without a sound methodology for performing this type of reconnaissance yourself, you are likely to miss key pieces of information related to a specific technology or organization—but trust me, the hacker won’t.”


“Foot printing is one of the most important steps and it must be performed accurately and in a controlled fashion.” Continue reading

Uses of free Unix-based Security Tools to Develope Secure Systems – Part 1


In today’s world it is very rare to find a business or an organisation that is not reliant on a computer network of some sort, whether it is a hospital, a school, large bookstore, small shop or even a home business. This sets a challenge for IT professionals around the world, especially with the increased number of network attacks that are happening every day. The challenge is how to keep these networks secure?

What is network security?

Network security to IT professionals doesn’t mean that a network is 100% secure because that is impossible unless you completely disconnect your network from the outside world and even that doesn’t protect the network from internal attacks or the physical theft of the computer and the data inside it. The only way to have 100% security is to power off all computers and for businesses these days that isn’t an effective decision. Continue reading

3. Media and Connectors Part 2

Coaxial cable – was used on networks in the olden days, however today’s networks moved on to faster and tougher cables. This is not to say that coaxial cables will no longer be encountered as some networks that used this type of cable might still do so because their environment is still the same and so they feel that there’s no need to upgrade.

English: A cutaway diagram of a coaxial cable

Image via Wikipedia

The above figure shows an example of a coaxial cable, which looks similar to the cables used for TVs.

There are two types of this cable Thick and Thin coaxial, although the two are no longer popular; out of the two thin coaxial is more popular. It’s about 0.25 inches in diameter and has a max length of about 185 meters and they use the BNC connector.

Continue reading

4. Wiring Standards and Specialised Cable

68A and 568B Standard

The Telecommunications Industry Association (TIA) and the Electronics Industry Association (EIA) have designed a wiring standard called 568A and 568B, which is used for the RJ-45 connectors on a UTP/STP cable. The number 568 refers to the order the wires within the Cat 5, Cat 3 and Cat 6 cables are terminated and attached to the connector. Both standards (568A and 568B) are the same in terms of the signal with a slight difference in the order the pins are terminated. They’re both used for patch cords in Ethernet networks. To be able to make these cables (in case you have to) you need to know which order to connect the wires to the connector. The following figure illustrates this, the pin numbers are read left to right while the connector tab facing down.

     Image taken from Mike Harwood’s Network+ Guide
Continue reading