Specifications

138 VH-2402-L3 Management Guide 9033691-01
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
Table 2-4. Binary to Decimal Conversion
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