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Tuesday, November 24, 2009

How to Compute an IP Subnet Mask

IP address is a code that has host and network parts. The host bits describe a particular PC. The network prefix shows a network; its measurement lengthwise depends on the class of network. Sub-netting helps to arrange a network by splitting it to several subnets. To describe such subnets, you should take bits from the portion of host of the IP address. That also expands the network prefix. The subnet mask openly describes network and host bits as 1/0, respectively.

In this instance, we will compute a subnet mask for a PC with IP address “ that goes to network with 6 subnets.

1. Step 1

Verify the network class A/B/C based on IP addresses:

* If the IP addresses start with 1 - 126, it is Class A.
* If the IP addresses start with 128 - 191, it is Class B.
* If the IP addresses start with 192 - 223, it is Class C.

In our illustration, the network is class C because the IP address begin with 192.

1. Step 2

Know the number of bits required to define subnets:

* Number of subnets = (2^ # of bits) - 2. Therefore,
* Number of bits = Log2(# of subnets + 2).

In our illustration, there are 6 subnets:

* Number of bits = Log2(6 + 2) = Log2(8) = 3. 3 bits in the IP address are utilized as a subnet portion.

1. Step 3

Create the subnet mask in a binary form by expanding the original subnet mask w/ subnet bits. Original subnet mask for class A - C are:

* 11111111.00000000.00000000.00000000 (Class A, network part = 8 bits)
* 11111111.11111111.00000000.00000000 (Class B, network part = 16 bits)
* 11111111.11111111.11111111.00000000 (Class C, network part = 24 bits)

In our illustration, an addition of the default “class C” subnet mask with three bits (Step 2) outcomes in the subnet mask

1. Step 4

Change the subnet mask binary to the decimal form. The binary form has 4 octets. Utilize the following rules:

* Write 255 for "1111111" octet.
* Write 0 for "00000000" octet.
* If octet has 1 and 0 utilize the formula:

Integer # is equals to (128 x n) + (64 x n) + (32 x n) + (16 x n) + (8 x n) + (4 x n) + (2 x n) + (1 x n)
Where N is “1” or “0” in the corresponding place in the sequence of octet.

In our illustration, for 11111111.11111111.11111111.11100000
11111111 = 255
11111111 = 255
11111111 = 255
11100000 = (128 x 1) + (64 x 1) + (32 x 1) + (16 x 0) + (8 x 0) + (4 x 0) + (2 x 0) + (1 x 0) = 224

The Subnet mask is “”.[]

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Monday, November 23, 2009

What is SAN or Storage Area Network?

A SAN or Storage Area Network
is a network that is separate from WANs and LANs. It is used to link all the storage resources linked to different servers. It consist a collection of SAN Software and SAN Hardware; the hardware has high interconnection rates among the different storage devices and the software configures the SAN and manages monitors.

Storage Area Network or SAN is a high speed sub-network of shared storage devices. A storage device is a machine that has nothing but disks for saving data. A Storage Area Network's architecture acts in a way that makes every storage devices accessible to every server on a WAN or LAN. As other storage devices are placed to a Storage Area Network, they too will be available from any server in the bigger network. In this case, the server only acts as a way between the user and the stored file or data.

A Storage Area Network is a storage devices network that is linked to each other and to a server, in some arrangements a Storage Area Network is also linked to the network. It is foretell to become the storage data technology of selection in the coming years.

Storage Area Networks originated to conquer the problems with NAS or network attached storage devices, which like ordinary servers are tough to handle and hard to expand the capability on. Network Attached Storage devices also put in to the traffic on the network and endure from the delays made by the OS’s network stacks.

A Storage Area Network is made of a lot of fabric switches linked in a network. The most known form of Storage Area Network utilizes the “Fiber Channel fabric protocol”. On the other hand, ISCSI can be utilized with IP switches. The Storage Area Network enables the storage on the hard drive in the Disk collection controllers to be connected among the servers.

One of the major benefits of Storage Area Network is that it makes things easier for the network infrastructure and simplifies to manage. This it does by means of virtualization, consolidation, integration, and automation. Consolidation targets at centralizing the storage to enhance scalability, lessening infrastructure complexity, and raising efficiency. Virtualization aids to enhance availability and lessens costs as it gives a wide view of storage devices. Automation of habit tasks enables the administrators to concentrate on vital tasks. Automation also enhances responsiveness. Integration aids organizations furnish users with the wanted info in a more systematic manner.[]

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Saturday, November 14, 2009

5 Minutes to Understanding Tcp/ip

What exactly is TCP/IP?

TCP/IP stands for Transmission Control Protocol/Internet Protocol. It is a software language and set of rules computers and/or devices use on a network to talk to each-other. TCP/IP is both a LAN (local area network) and WAN (wide area network) protocol. A WAN spans a great distance. The internet
is the biggest WAN in existence. A protocol is a set of rules as well as a software language used in order to transmit services, identify information, and identify computers. TCP/IP is a very scalable (able to grow and support new or different services and computers), robust (reliable) protocol. This is mainly why it was elected a long time ago to be the default internet protocol. In order for two computers to exist and effectively communicate they must either:

A. Both be using the same protocol


B. Use an intermediary program to interface and act as an interpreter between the two different protocols.

In this situation example A. is the most ideal and common when speaking of computers existing and effectively communicating on the internet. If you are speaking "english" and I am speaking "german" you would not be able to understand me, correct? Computers are the same way. The language and set of rules that computers and devices use to speak and identify each-other on the internet guessed is TCP/IP. Right now we use the version known as TCP/IP v4. The v4 stands for "version 4". We are starting to ever so slowly move to TCP/IP version 6. At the time this article is written (January, 2008) TCP/IP v6 is certainly not common place. However in the future we will inevitably all need to be able to use it as it becomes the default TCP/IP protocol.

Where is TCP/IP exactly?

This software is, by default, installed in almost every operating system used today. It is already there within your Windows, Macintosh, or Linux operating system when you start your computer. Programmers have it already pre-installed and integrated with your operating system right out of the box.

Can you uninstall TCP/IP?

Yes, in most operating systems you can. However situations in why you would do such is beyond the scope of this article and you, as the general computer user would almost never (I know, "never say never". OK 99.999 % of the time the common computer user would never need to do such).

In order to use TCP/IP on the internet you need three common parameters. They look like this:

IP Address:

Default Gateway Address:

Subnet Mask:

These parameters or TCP/IP settings can be accessed or viewed in your operating system. Every operating system will have at least one place where you can see and if needed change these IP settings.NOTE: If you are a new user and are not having any connectivity issues I would leave these settings as is for now.

What is an IP Address?

When using the TCP/IP protocol a machine, and or website needs an identifier. This identifier is an "Ip Address". It is actually 32 ones and zero's. However using simple decimal shorthand you can break this down to normal "decimal" numbers which is what we generally see. Hence an IP address is four separate decimal numbers separated by an period. IP Addresses look like this:

This number identifies your machine. This way other computers know where to find you and/or who to respond to on the internet when you request any service or want to browse around online. In order for computers on the internet not to get confused, no two machines, or websites can have the same IP address. They all must be "unique" to the machine or website.

What is a Default Gateway Address?

A "default gateway" IP address is needed as well. this is the IP address of the machine you use to get onto the internet through. It is a doorway so to speak. Every internet based machine goes out to the internet through a "default gateway". This is normally a server or a router.

A default gateway machine also has an IP address. It is known as the "gateway address" or gateway IP.

Your computer as an internet machine also needs this IP configured.

What is the Subnet Mask?

A subnet mask , to put it as simple as possible is a indicator address that does two things.

1. identifies your internet service provider network and this networks size. 2. Helps machines narrow in on your exact location when sending information to you but this is out of the scope of this article. For now just understand it's basis and understand you need one in order to access and exist on the internet.

So now you know what an IP address, a gateway address, and what a subnet mask address is. These are the internet settings (aka IP Parameters) every machine needs to access the internet.

So how and where do you get them? Well you can manually configure your own every time you log in or start your computer. You should contact your internet service provider to ask what your assigned IP, default gateway address, and subnet mask should be. However this would be a pain in the neck wouldn't it?

This is where DHCP (dynamic host configuration protocol) comes in. We will discuss this in the near future. []

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Thursday, November 12, 2009


This address is utilized by Linksys routers and open source linux based firm wares that are well matched with Linksys routers.As a result is apt to be set as default gateway on PCs connected to a router. as well commonly includes web interface which controls the configuration of the router. If you are can’t access this address it is likely that you need some kind of network configuration issue.

The IP address is the default for the Linksys brand-home for broadband routers. The manufacturer at the factory sets this IP, but you could change it any time utilizing the network administrative console of the router.

IP address is a private IP v4 network address. Any brand of the router’s network, or any PC on a limited network for that issue, could be set to utilize this address. As with any other Internet Protocol address, however, only a single device on the network must utilize to prevent address conflicts. is a Class C private Internet Protocol address. Private Internet protocol addresses are preserved for private networks which are not included on the Internet. Though most home networks are linked to internet, they’re not part of it. Instead, the network router operates as the gateway and routes network data to correct PC on the home network. While this permits a lot of PCs to share single Internet Service Provider connection the disadvantage is that home PCs are not reachable right away from the Internet (but given the number of trojans and viruses out there this could also be a great thing).[]

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Tuesday, November 10, 2009

How to Implement Wireless VLANS

The wireless access points operate as bridges with no routing defined anywhere on the wireless network segment. All VLANs are defined on the wired switches and mapped with specific SSIDs at each access point. The maximum number of VLANs and SSIDs per access point that can be mapped is 16. The wireless client attaches or associates with a specific SSID which in turn will map client with membership in a specific VLAN.

There is an option to configure the maximum number of wireless client associations allowed per SSID improving network performance and availability. The access point is assigned a primary SSID with the 802.11 standard, advertising it with beacons on that segment to all wireless clients. There is a guest SSID defined that companies should define a VLAN policy for that group or with access control list security policies denying access to the corporate network. Guest traffic for the most part should be directed across the internet unless they have specific network rights.

VLAN membership of each wireless client is assigned considering what servers are most accessed, specific company department and security rights. Device types such as a scanner with less security won't be assigned the same VLAN as an engineering group with sensitive information and 802.1x security.

VLAN 1 is the default native VLAN and doesn't tag traffic. The native VLAN number assigned on the wired switches must match the VLAN assigned at all attached access points on that network segment. The native VLAN is sometimes assigned to network management traffic or the RADIUS server. Companies will implement access control lists at each network switch to filter traffic securing the management VLAN traffic. With most designs the native VLAN isn't mapped to a SSID except with connecting root bridges and non root bridges. Define an infrastructure SSID for infrastructure devices such as a repeater or workgroup hub and map the native VLAN allowing those devices to associate with non root bridge and root bridges.

Wireless clients configured with 802.1x authentication will have a RADIUS server configured with mapped SSIDs per wireless client. This is called RADIUS SSID control. The server sends the list to the access point where the client is allowed to associate with an access point should they be a member of one or several SSIDs. RADIUS VLAN control assigns each client with a specific VLAN and default SSID. The mapping can be overridden with the RADIUS sever configuration. During authentication the wireless client is assigned to that specific VLAN. The employee however can't be a member of any wired VLAN except that. Policy group filters or class map policies can be defined per VLAN. You should deny all infrastructure devices to be members of any non-infrastructure SSID. Wireless clients will see all broadcasts and multicasts of all mapped VLANs unless 802.1x per VLAN encryption is implemented with TKIP, MIC and broadcast keys.

Trunking is implemented to switch traffic between network segments that have multiple VLANs defined. Each VLAN defines a separate broadcast domain comprised of a group of employees with a company department. The trunk is a physical switch port interface with defined Ethernet subinterfaces configured with 802.1q or ISL encapsulation. Those packets are tagged with specific VLAN number before it is sent between access point and wired network switch. The access point Ethernet interface is configured as a hybrid trunk. Access control lists should be defined at the wired switch Ethernet interface that drops packets from VLANs not defined with any SSID.

VLAN 100 = 192.168.37.x - SSID = Engineers

VLAN 200 = 192.168.38.x - SSID = Guest

VLAN 300 = 192.168.39.x - SSID = Sales

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