Internet IP Subnetting

Internet IP Subnetting

IP Subnetting is a method of segmenting hosts within a network and providing additional structure. Without subnets, an organization operates as a flat network. These flat topologies result in short routing tables, but as the network grows, the use of bandwidth becomes inefficient.

Routers use a subnet mask to determine which parts of the IP address correspond to the network, the subnet, and the host. The mask is a 32-bit number in the same format as the IP address. The mask is a string of consecutive is starting from the most significant bits representing the network ID, followed by a string of consecutive Os representing the host ID.

IP Address	Network		Host
	128 10000000	10 00001010	173 10110010	46 00101110

Subnet Mask	Network		Subnet	Host
	255 11111111	255 11111111	255 11111111	0 00000000

This subnet mask can also be written as "/24", where 24 represents the number of 1s in the subnet mask.

Each address class has a default subnet mask (A=/8, B=/16, C=124). The default subnet masks only the network portion of the address; the effect is no subnetting. With each bit of subnetting beyond the default, you can create 2-2 subnets. The preceding example has 254 subnets, each with 254 hosts.

Identifying Subnet Addresses
Given an IP address and subnet mask, you can identify the subnet address, broadcast address, and the first and the last usable addresses within a sub- net as follows:

• Write the 32-bit address and subnet mask below that (the following figure shows 174.24.4.176/26).
• Draw a vertical line just after the last 1 bit in the subnet mask.
• Copy the portion of the IP address to the left of the line. Place all Os for the remaining free spaces to the right. This is the subnet number.
• Copy the portion of the IP address to the left of the line. Place all is for the remaining free spaces to the right. This is the broadcast address for the subnet.
• You can also find the first and last address by placing ...000i and ...iliO respectively in the remaining free spaces.

174.24.4.176	1010111000110000000100	10|110000	Host
255.255.255.192	1111111111111111111111	11|000000	Mask
174.24.4.128	1010111000110000000100	10|000000	Subnet
174.24.4.191	1010111000110000000100	10|111111	Broadcast

Hacking Explained

Hacking Explained

Anyone who accesses a public network should know about hackers and their methods. Failure to understand what they do can leave you and your network exposed.

Although thieves and opportunists always go after an easy target versus a difficult (or well-prepared) one, some hackers specifically choose difficult targets, such as government offices or networking companies, solely for bragging rights.

Hacking really boils down to a few activities:

• Breaking in�'Breaking into a private network is usually the first part of any hacking scheme. (A denial-of-service [DoS] attack is one notable exception.) Most break-ins require a password (which are guessed or stolen), but hackers find other ways to get in as well.
• Breaking stuff�'Once in a network, many hackers (anarchists in particular) try to break or disable the entire network, or specific parts of it, such as web servers. If they destroy data or disrupt business, recovery can be expensive for the attacked company.
• Stealing stuff�'Like most thieves, many hackers are motivated by greed. They might sell plans, schematics, or intellectual property to unscrupulous individuals, companies, or government agencies.

Hacks and Attacks
An attack in network speak refers to any attempt to break into a compute network, or packet, as well as any attempt to launch a malicious or self-replicating program. Attacks fit into multiple categories, many of which are described here.

All network attacks are either active or passive.

Active attacks include injecting malicious files, altering data, or clogging the network. In theory, you can detect active attacks but not passive attacks.

Passive attacks such as eavesdropping do not actually cause harm to the network, but hackers can use them to obtain information that enables active attacks. People looking for passwords can tirelessly try every combination until they find a working password (a brute-force attack). Man-in-the-middle attacks occur when a hacker interposes between two valid users and eavesdrops for passwords. Passive attacks are difficult to detect.

Remote attacks are conducted by people outside the network (those without a network ID), whereas local attacks use an existing account to exploit the system.

Hit-and-run attacks quickly crash systems, whereas persistent attacks affect the victims only as long as the attack lasts.