Information Technology Reference
In-Depth Information
Mask Nomenclature
There are several ways to represent IP subnet masks. The mask can be binary, hexadecimal,
dotted decimal, or a prefix “bit mask.” Historically, the most common representation was
the dotted-decimal format (255.255.255.0). The prefix bit mask format is now more popu-
lar. This format represents the mask by using a slash followed by the number of leading
address bits that must be set to 1 for the mask. It is also referred to as classless interdo-
main routing (CIDR) prefix notation. For example, 255.255.0.0 is represented as /16.
Ta ble 8 -1 6 shows most of the mask representations. The /24 mask is common on LAN
segments. The /30 mask is common for WAN point-to-point links, and /32 is used for
router loopback addresses.
Ta b l e 8 -1 6
Subnet Masks
Dotted Decimal
Bit Mask
Hexadecimal
255.0.0.0
/8
FF000000
255.192.0.0
/10
FFC00000
255.255.0.0
/16
FFFF0000
255.255.224.0
/19
FFFFE000
255.255.240.0
/20
FFFFF000
255.255.255.0
/24
FFFFFF00
255.255.255.128
/25
FFFFFF80
255.255.255.192
/26
FFFFFFC0
255.255.255.224
/27
FFFFFFE0
255.255.255.240
/28
FFFFFFF0
255.255.255.248
/29
FFFFFFF8
255.255.255.252
/30
FFFFFFFC
255.255.255.255
/32
FFFFFFFF
IP Address Subnet Design
The development of an IP address Plan or IP address subnet design is an important con-
cept for the network designer. You should be capable of creating an IP address plan based
on many factors:
Number of locations
Number of devices per location
 
 
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