A Virtual Private Network (VPN) is a network technology which extends private network (such as LAN) over a public network such as the Internet. A VPN allows a computer (or a network) to be connected securely as if they are physically wired together. Corporations use VPN to allow remote workers to connect securely to their private network. A VPN is also used to interconnect remote offices with a head office as if they are physically connected.

You have a private or public network with servers and workstations that are assigned static and dynamic IP addresses (either private or public IPs). You assigned them the static IP addresses due to NAT (Network Address Translation) or for public access, and dynamic IP addresses via the DHCP. Even if you kept a good record of those assigned IPs, there are times when you want to find all IP addresses of networked devices. The following procedure may be used to determine IP addresses of networked devices that are connected to your network.

Often times we see a networked printer suddenly stop working and you need to find a static (private) ip address of the printer to diagnose further. How do we find IP address of a networked printer? There are a few different ways to go about finding it.

RJ-45 conductor data cable contains 4 pairs of wires each consists of a solid colored wire and a strip of the same color. There are two wiring standards for RJ-45 wiring: T-568A and T-568B. Although there are 4 pairs of wires, 10BaseT/100BaseT Ethernet uses only 2 pairs: Orange and Green. The other two colors (blue and brown) may be used for a second Ethernet line or for phone connections. The two wiring standards are used to create a cross-over cable (T-568A on one end, and T-568B on the other end), or a straight-through cable (T-568B or T-568A on both ends).

The two methods described below are extracted from the lartc howto. It is included here to provide a complete reference. For latest updates, please view source document.

Denial of service attacks are major nuisance for web hosts, and as a web host you'll have to take every measure to protect your resources from DoS attacks. Our APF, BFD, DDoS and RootKit article describes Linux utilities available to protect from DDoS attack, and also explains installation procedures. This article supplements above article by providing means to control traffic (bandwidth shaping) with Linux "tc" command so that no single machine can waste the entire network bandwidth.

Being a web host, your servers are constantly being attacked by hackers by denial-of-service (DoS) and other brute force attacks. There is no foolproof method to stop 100% of all attacks, but there are ways to protect your servers by applying firewall rules, and detecting and banning attacking IPs.

DoS attack, denial-of-service attack, is an explicit attempt to make a computer resource unavailable by either injecting a computer virus or flooding the network with useless traffic. In simple words, it is similar to thousands of people trying to enter a room from a single entrance, ultimately causing havoc. This not only disturbs the normal operations of the network but also results in poor performance and system breakdown due to overwhelming requests. A large-scale DDoS attack (ranges up to 400 GBps) can affect the internet connectivity of an entire geographical region. There are two types of DoS attacks: computer attack and network attack. Common forms of denial of services attacks are:

IP Spoofing is a technique used to gain unauthorized access to machines, whereby an attacker illicitly impersonates another machine by manipulating IP packets. IP Spoofing involves modifying the packet header with a forged (spoofed) source IP address, a checksum, and the order value. Internet is a packet switched network, which causes the packets leaving one machine may be arriving at the destination machine in different order. The receiving machine resembles the message based on the order value embedded in the IP header. IP spoofing involves solving the algorithm that is used to select the order sent values, and to modify them correctly.

Ipconfig is a MS-DOS command-line tool used to display and manage the network settings of your computer. Ipconfig is available on Windows machines, and it displays the current network connection details and DHCP client settings.