Networking Reviews

What is a Torrent – All about the Torrent Protocol

A Torrent is a peer-to-peer technology that uses small files containing information about a specific (usually large) file. This information is about the users having the file, and essentially plays the role of liaison between users. The size of torrent files is very small and has an extension of .torrent. The protocol used to exchange files, is the BitTorrent protocol. Basically we are sharing files that are not in a central server, but rather on the computers of other users. What is important to stress out here is that when we download a file we also upload it the same time (if there is a demand for this file).

Torrent Clients

Torrent clients are the programs we use to connect with other users and to manage the torrents. There are several different options. The most popular (free) torrent client programs are:

uTorrent (www.utorrent.com)
This is a very light client that does not even need installation (although there is also a version that you can install) with several features. Recently has become very popular as a client and has also introduced a public beta version of uTorrent WebUI, which allows users to control downloads from any computer.

Azureus (http://azureus.sourceforge.net)
It is a powerful client with great potential and a very large set of parameters. You need java installed to work and is very popular. The disadvantage of this client is that its too heavy as a program.

BitComet (http://www.bitcomet.com)
It is a very powerful and light client. It is built in C++ and incorporates a browser as well. It is considered to be very quick in downloading.

Where do I find Torrents

Torrents can be found at various sites offering such content. Usually these site are called trackers and are either open to everyone (which reduces the credibility of their content) or closed (communities) with limited members. In the second case, usually the content is more remarkable and trusted, while the speeds achieved are also better. For example I would mention only one tracker, the linuxtracker.org, where you can find open-source software, Linux distributions, etc.

Torrent Terminology

Seeders
These are users who have in their possession the entire file which we want to download, and they make the file available to others.

Leechers
These are users not having in their possession the entire file but part of it and are in the process of downloading.

Please note here that when someone is a leecher, and downloads a file, then at the some time he also uploads the file to other leechers interested for the particular file.

Ratio
The ratio is a number that comes out of the division of the Mbytes that the user has uploaded divided by the Mbytes that the user has downloaded. So if a user has uploaded to the community a total of 1.8 GB and has downloaded 3 GB, then he has a ratio of 1.8 / 3 = 0.6. From the above we can get the golden rule of torrents, that for each file we download, we must hold it (seed it) at least until its ratio becomes 1 so that we offer to the community as much as we received.
Some communities have rules on the ratio of users and there are several «punishments» for low ratio, such as getting banned from the site, lower speeds and / or major delays. Open torrent sites usually do not have such restrictions.

How does Trackers Work
Let us see into more detail of how trackers work.
A tracker hosts only the files ending in .torrent, not the files that are being downloaded. These files exist only on the computers of users. The process of communication is as follows. The A user visits a tracker and selects among the many available records a file to download, lets say the ubuntu.iso. He requests the tracker to obtain the .torrent file which describes ubuntu.iso. From the torrent file, user A learns that users B and C have the whole ubuntu.iso file and that user D has only 25% of the file. Now is the turn of the client (e.g of utorrent) to do its job. The program sends requests to users B, C and D for ubuntu.iso, and once the clients of these users respond, the transfer of the file begins.

Ethernet Network Cable – Cat5 – Cat5E – Cat6

Ethernet cables are the most common network cables you will encounter. All networked devices on a Local Area Network (LAN), such as your PC, a network printer, a networked copy machine, a Server (Windows or Unix) etc use an Ethernet Cable to communicate with the rest devices on the network. Ofcourse, each of these devices is connected to an Ethernet Switch which is the heart of a LAN network.

The standard Ethernet network cable used today is the Cat5 or Cat5E (Enhanced) which is a twisted pair cable containing four pairs of copper wires. Some installations also use Cat6 type which is the newer version supporting higher data rates. The connector used for ethernet cables is the 8-pin RJ45 connector plug, as shown in the figure below.

RJ45 Ethernet Connector Plug Twisted Pair UTP ethernet cable

ethernet patch network cable

All Ethernet cables support communication over distances of 100m. The older Cat5 cable uses only two pairs to support 100Mbps (Fast Ethernet). The enhanced version Cat5E uses all four wire pairs to support data rates of 1000Mbps (Gigabit Ethernet). Cat6 types support 10Gbps (ten Gigabit) data rates.

Straight Through Vs Crossover Cable

Normally you will need a straight through cable to connect your PC, server, network printer etc. Whatever is connected to a Network switch uses straight through cable. However, whenever you connect two “similar” devices together ( e.g PC with PC, switch with switch, router with router) you need a crossover cable. This looks the same as the straight cable, but the internal wires are connected differently on the RJ45 connector.

How to configure static IP address on a Windows Computer

By default, the network interface card setting for a windows computer is configured to receive a dynamic IP address from a DHCP server. However, it is sometimes necessary to assign a static IP address to your Home Network Computer or to a server on your Local Area Network. Assigning a static IP to your Home Computer is a good security practice since you can configure your Home Internet Router to allow access to the Internet to only that specific IP address. Also, for LAN servers is a must to have static IP addresses assigned to them since these servers might need to be accessed from the Internet (therefore you will need a static NAT translation), and also you will need a static DNS binding of the server domain name with its static IP address.

In this post I will show an example configuration to setup a static IP address for a Windows XP computer. Similar settings are used for almost all Windows versions. Lets start: [Read more…]

What is DHCP – Simple Description

DHCP Stands for Dynamic Host Configuration Protocol. It is one of the most useful protocols used to enable IP communication between Networked devices (Computers, Servers, Routers, etc).

As we know, in order for two networked devices to communicate, it is absolutely necessary that they have an IP address assigned on their Network Interface Card (NIC). A network administrator can either assign manually a static IP address for each device, or have the address assigned dynamically. Now, imagine a network with thousands of network devices (PCs, Laptops, Network Printers etc). It would have been a daunting task for the Admin to manually configure an IP address for each device and keep track of them all. Fortunately, DHCP provides a way to dynamically assign IP addresses from a DHCP Server to DHCP clients. The diagram below shows a simple DHCP network.
 

 

Here is a plain English DHCP “conversation” between the DHCP clients and the server:

DHCP Client: I don’t have an IP address assigned. Is there a DHCP server on the LAN Network ?
DHCP Server: Yes, Here I am.
DHCP Client: I need an IP address. Can you provide me one, together with the IP addresses for my Gateway and DNS servers?
DHCP Server: Sure, you can take IP address 10.1.1.1 for 3600 seconds. Your Gateway address is 10.1.1.254 and your DNS address is 10.1.1.200.
DHCP Client: Thanks

Networking Technologies on the Rise

According to Gartner analysis, the following networking and telecommunication technologies are emerging and are expected to be adopted in the mainstream market within 5 to 10 years.

  • LTE-A: Long Term Evolution Advanced for mobile networks is a technology that will increase mobile data rates to 1Gbps (Downlink) and 500 Mbps (Uplink). The maturity of this technology is however considered embryonic.
  • SSL Peer-to-Peer, Site-to-Site Virtual Private Networks: This technology will be used between individual hosts to create secure SSL meshed connections that can enable peer-to-peer (P2P) communications and emulate a corporate network without the use of boundary routers and distributed remote LANs. Potential uses include virtual private network (VPN) connections to branch offices via wireless data services and contractor access scenarios.
  • Energy Efficient Ethernet (802.3az): This is an IEEE initiative to create an ethernet standard that will have reduced power demands. The primary approach will be to enable Ethernet to dynamically change speed (without losing a connection) to reduce power requirements during times when demand is lower. Standardization is expected in 2010.
  • Fiber Channel over Ethernet: FcoE purpose is to provide a lower overhead protocol compared with iSCSI for transporting storage traffic over 10 Gbps Ethernet connections. One of the benefits of this standard will be the consolidation of adapters/NICs and switches, instead of having redundant sets of storage and networking.
  • 4G Standard: The fourth generation standard for mobile cellular networks is expected to become commercial between 2012 and 2015. Many technologies are
    competing for inclusion in the 4G standard, but they share common features such as orthogonal
    frequency division multiplexing (OFDM), software-defined radio (SDR) and multiple input, multiple
    output (MIMO). 4G technology will be packet-switched.
  • VoIP Wireless WAN: Voice over Internet Protocol (VoIP) wireless wide-area network (WWAN) is the use of IP in the wireless link for “packetized” voice transmission, as compared with circuit-switched.

IPv6 Addresses Explained

A recent study by RIPE (the European Internet Registry for IP addresses) has warned that by 2011 the current version of IP addresses (IPv4) will be depleted, thus it urged all professional bodies and organizations dealing with the Internet to actively adopt and support the new IPv6 address version.

IPv6 addresses are 128 bits long-much longer than the current 32-bit IPv4 address. As we know, the 32-bit IPv4 address scheme supports around 4 billion IP addresses. The new IPv6 version, will support 2 to the 128th power of IP addresses, which is a number that even mathematicians will have a hard time to count!! [Read more…]

Multimedia Traffic Issues Through a Firewall

Multimedia applications (such as RealAudio, VoIP Telephony, Video Streaming etc) were always an issue when passing through a network firewall. These kind of applications behave in unique ways:

  • They use dynamic ports.
  • They transmit request using TCP and get responses in UDP or TCP.
  • They use the same port for source and destination.
  • For each multimedia request, the multimedia server might send numerous streams of data in reply.

All the above impose an “unacceptable” traffic behavior for a network firewall, thus multimedia traffic needs some special treatment in order to be permitted through the firewall. [Read more…]

IANA Well Known Ports

The Well Known Ports are assigned by the IANA and on most systems can only be used by system (or root) processes or by programs executed by privileged users.

Ports are used in the TCP [RFC793] to name the ends of logical connections which carry long term conversations. For the purpose of providing services to unknown callers, a service contact port is defined. This list specifies the port used by the server process as its contact port. The contact port is sometimes called the “well-known port”.

To the extent possible, these same port assignments are used with the  UDP [RFC768].

The range for assigned ports managed by the IANA is 0-1023.

Port Assignments: [Read more…]