Support page

Items that make your computer life easier!! 

Nat Tables and links

Download Support files

 

VNC Viewer

 

 

 

 

 

 

Subnet Masks: Decimal and CIDR

CIDR Decimal Mask Old A Subnets B Subnets C Subnets # Useable # Hosts
8 255.0.0.0 A 1 16,777,214 16,777,216
9 255.128.0.0 A 2 8,388,606 8,388,608
10 255.192.0.0 A 4 4,194,302 4,194,304
11 255.224.0.0 A 8 2,097,150 2,097,152
12 255.240.0.0 A 16 1,048,574 1,048,576
13 255.248.0.0 A 32 524,286 524,288
14 255.252.0.0 A 64 262,142 262,144
15 255.254.0.0 A 128 131,070 131,072
16 255.255.0.0 B 256 1 65,534 65,536
17 255.255.128.0 B 512 2 32,766 32,768
18 255.255.192.0 B 1,024 4 16,382 16,384
19 255.255.224.0 B 2,048 8 8,190 8,192
20 255.255.240.0 B 4,096 16 4,094 4,096
21 255.255.248.0 B 8,192 32 2,046 2,048
22 255.255.252.0 B 16,384 64 1,022 1,024
23 255.255.254.0 B 32,768 128 510 512
24 255.255.255.0 C 65,536 256 1 254 256
25 255.255.255.128 C 131,072 512 2 126 128
26 255.255.255.192 C 262,144 1,024 4 62 64
27 255.255.255.224 C 524,288 2,048 8 30 32
28 255.255.255.240 C 1,048,576 4,096 16 14 16
29 255.255.255.248 C 2,097,152 8,192 32 6 8
30 255.255.255.252 C 4,194,304 16,384 64 2 4
31 255.255.255.254 C N/A N/A N/A N/A N/A
32 255.255.255.255 C BC BC BC Broadcast Broadcast

Notes:

  1. The "# Useable" series can be derived by "previous # Useable x 2 + 2".
  2. The "# Useable" series can be derived by "# Hosts - 2".
  3. The "# Hosts" series can be derived by "previous # Hosts * 2".
  4. The "# Hosts" series can be derived by "# Useable + 2".
  5. The number of subnets is only correct under CIDR. Using the old classfull numbers it is "# CIDR Subnets - 2".

RFC1918: Address Allocation for Private Internets

URL: http://www.faqs.org/rfcs/rfc1918.html

Excerpt:

3. Private Address Space

 The Internet Assigned Numbers Authority (IANA) has reserved the
 following three blocks of the IP address space for private internets:

 10.0.0.0 - 10.255.255.255 (10/8 prefix)
 172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
 192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

 We will refer to the first block as "24-bit block", the second as
 "20-bit block", and to the third as "16-bit" block. Note that (in
 pre-CIDR notation) the first block is nothing but a single class A
 network number, while the second block is a set of 16 contiguous
 class B network numbers, and third block is a set of 256 contiguous
 class C network numbers.

 An enterprise that decides to use IP addresses out of the address
 space defined in this document can do so without any coordination
 with IANA or an Internet registry. The address space can thus be used
 by many enterprises. Addresses within this private address space will
 only be unique within the enterprise, or the set of enterprises which
 choose to cooperate over this space so they may communicate with each
 other in their own private internet.