D-Link DES-3326SR Layer 3 Switch
The dots are included to make the numbers easier to read.
Eight binary bits are called a ‘byte’ or an ‘octet’. An octet can represent any decimal value between ‘0’ (00000000) and
‘255’ (11111111). IP addresses, represented in decimal form, are four numbers whose value is between ‘0’ to ‘255’. The
total range of IP addresses are then:
Lowest possible IP address -
0.0.0.0
Highest possible IP address -
255.255.255.255
To convert decimal numbers to 8-bit binary numbers (and vice-versa), you can use the following chart:
Binary to Decimal Conversion
Binary Octet Digit
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
Decimal Equivalent
128
64 32 16 8 4 2 1
Binary Number
128+64+32+16+8+4+2+1=
255
1 1 1 1 1 1 1 1
Each digit in an 8-bit binary number (an octet) represents a power of two. The left-most digit represents 2 raised to the 7
th
power (2x2x2x2x2x2x2=128) while the right-most digit represents 2 raised to the 0
th
power (any number raised to the 0
th
power is equal to one, by definition).
IP addresses actually consist of two parts, one identifying the network and one identifying the destination (node) within the
network.
The IP address discussed above is one part and a second number called the Subnet mask is the other part. To make this a bit
more confusing, the subnet mask has the same numerical form as an IP address.
Address Classes
Address classes refer to the range of numbers in the subnet mask. Grouping the subnet masks into classes makes the task of
dividing a network into subnets a bit easier.
There are 5 address classes. The first 4 bits in the IP address determine which class the IP address falls in.
•
Class A addresses begin with 0xxx, or 1 to 126 decimal.
•
Class B addresses begin with 10xx, or 128 to 191 decimal.
•
Class C addresses begin with 110x, or 192 to 223 decimal.
•
Class D addresses begin with 1110, or 224 to 239 decimal.
•
Class E addresses begin with 1111, or 240 to 254 decimal.
Addresses beginning with 01111111, or 127 decimal, are reserved. They are used for internal testing on a local machine
(called loopback). The address 127.0.0.1 can always be pinged from a local node because it forms a loopback and points
back to the same node.
Class D addresses are reserved for multicasting.
Class E Addresses are reserved for future use. They are not used for node addresses.
The part of the IP address that belongs to the network is the part that is ‘hidden’ by the ‘1’s in the subnet mask. This can be
seen below:
•
Class A
NETWORK.node.node.node
•
Class B
NETWORK.NETWORK.node.node
188
•
Class C
NETWORK.NETWORK.NETWORK.node
Содержание DES-3326SR
Страница 240: ......
