ACS CFSound-IV, Manual

Page: 24 / 73

The CFSound-IV can utilize a static, user-configured IP address/mask or a dynamic NAT assigned IP
address/mask (DHCP client).
IP Mask
A sub-network or subnet is a logically visible subdivision of an IP network. All computers that belong to
the subnet are addressed with a common, identical, most-significant bit-group in their IP Address. This results
in the logical division of an IP Address into two fields; a network or routing prefix and the host identifier:
Creating a subnet by dividing the host identifier
Network Prefix Host Identifier
↓ ↓ ↓
Network Prefix Subnet Number Host Identifier
The process of sub-netting involves the separation of network prefix and subnet number portion of the IP
Address from the host identifier. This is performed by a bitwise AND operation between the IP Address and
the IP Mask. The result yields the network address or prefix and the remainder is the host identifier. Here is
an example showing the separation of the network prefix and the host identifier from an IP Address
(192.168.1.200) and IP Mask (255.255.255.0):
Binary form Dotted-decimal notation
IP Address 11000000.10101000.00000001.11001000 192.168.1.200
IP Mask 11111111.11111111.11111111.00000000 255.255.255.0
Network prefix 11000000.10101000.00000001.00000000 192.168.1.0
Host identifier 00000000.00000000.00000000.11001000 0.0.0.200
The purpose of sub-netting is to divide a network into smaller subnets. This is achieved by designating
some high-order bits from the host part and grouping them with the network mask to form the IP Mask. Here
the previous example is modified by moving two bits from the host part to the IP mask to form four smaller
subnets one quarter the previous size:
Binary form Dotted-decimal notation
IP Address 11000000.10101000.00000001.11001000 192.168.1.200
IP Mask 11111111.11111111.11111111.11000000 255.255.255.192
Network prefix 11000000.10101000.00000001.11000000 192.168.1.192
Host identifier 00000000.00000000.00000000.00001000 0.0.0.8
The host identifier of all zeroes is reserved for the network ID, and the host identifier of all ones is
reserved for the broadcast address, so in general the number of hosts on a subnet is 2
N
-2 where N is the
number of bits reserved for the host portion of the address. For a 24-bit prefixed network:
Network
prefix size
IP Mask
Available
subnets
Usable Hosts
per subnet
Total usable
Hosts
24-bits 255.255.255.0 1 254 254
25-bits 255.255.255.128 2 126 252
26-bits 255.255.255.192 4 62 248
27-bits 255.255.255.224 8 30 240
28-bits 255.255.255.240 16 14 224
29-bits 255.255.255.248 32 6 192
30-bits 255.255.255.252 64 2 128
31-bits 255.255.255.254 128 2 (point-to-point) 256
Router IP Address
In computer networking a router is a node that connects two networks – such as a private network and the
public Internet. The host devices on the private network send IP packets addressed to IP Addresses on the
private network by resolving the destination MAC address into a destination IP Address through an Address