# Ip Y Sub Redes

Páginas: 7 (1624 palabras) Publicado: 17 de mayo de 2012
Diseño de subredes
Subnet Design Considerations
The deployment of an addressing plan requires careful thought on the part of the network administrator. There are four key questions that must be answered before any design should be undertaken.
1) How many total subnets does the organization need today?
2) How many total subnets will the organization need in the future?
3) Howmany hosts are there on the organization’s largest subnet today?
4) How many hosts will there be on the organization’s largest subnet in the future?
Subnet Example #1
Given
An organization has been assigned the network number 193.1.1.0/24 and it needs to define six subnets. The largest subnet is required to support 25 hosts.
Since 8 = 2^3,three bits are required to enumerate the eight subnets in the block. In this example, the organization is subnetting a/24 so it will need three more bits, or a/27, as the extended-network-prefix. A 27-bit extended-network-prefix can be expressed in dotted-decimal notation as 255.255.255.224. this is illustrated in Figure 11.

A 27- bit extended-network-prefix leaves 5 bits to define hostaddresses on each subnet. This means that each subnet work with 27-bit-prefix represents a contiguous block of 2^ 5 (32) individual IP addresses. However, since the all-0s and all-1s host addresses cannot be allocated, there are 30 (2^5 -2) assignable host addresses on each subnet.

Defining Each of the Subnet Numbers
In general, to define Subnet #n, the network administrator places the binaryrepresentation of n into the bits of the subnet-number field. For example, to define Subnet #6, the network administrator simply places the binary representation of 6 (110 base binary) into the 3-bits of the subnet-number field.
Base Net: 11000001.00000001.00000001 .00000000 = 193.1.1.0/24
Subnet #0: 11000001.00000001.00000001 .000 00000 = 193.1.1.0/27
Subnet #1: 11000001.00000001.00000001.001 00000 = 193.1.1.32/27
Subnet #2: 11000001.00000001.00000001 .010 00000 = 193.1.1.64/27
Subnet #3: 11000001.00000001.00000001 .011 00000 = 193.1.1.96/27
Subnet #4: 11000001.00000001.00000001 .100 00000 = 193.1.1.128/27
Subnet #5: 11000001.00000001.00000001 .101 00000 = 193.1.1.160/27
Subnet #6: 11000001.00000001.00000001 .110 00000 = 193.1.1.192/27
Subnet #7:11000001.00000001.00000001 .111 00000 = 193.1.1.224/27

Defining Host Addresses for Each Subnet
According to Internet practices, the host-number field of an IP address cannot contain all 0-bits or all 1-bits- The all-0s host-number identifies the base network (or subnet work) number, while the all-1s host-number represents the broadcast address for the network (or subnet work).

In general, todefine the address assigned to Host #n of a particular subnet, the network administrator places the binary representation of n into the subnet’s host-number field. For example, to define the address assigned to Host #15 on Subnet #2, the network administrator simply places the binary representation of 15 (01111 base binary) into the 5-bits of Subnet #2’s host-number field.
The valid host addressesfor Subnet #6 are given below. The underlined portion of each address identifies the extended-network-prefix, while the bold digits identify the 5-bit host-number field:

Subnet #6: 11000001.00000001.00000001 .110 00000 = 193.1.1.192/27
Host #1: 11000001.00000001.00000001.110 00001 = 193.1.1.193/27
Host #2: 11000001.00000001.00000001.110 00010 = 193.1.1.194/27
Host #3:11000001.00000001.00000001.110 00011 = 193.1.1.195/27
Host #4: 11000001.00000001.00000001.110 00100 = 193.1.1.196/27
Host #5: 11000001.00000001.00000001.110 00101 = 193.1.1.197/27
.
.
Host #15: 11000001.00000001.00000001.110 01111 = 193.1.1.207/27
Host #16: 11000001.00000001.00000001.110 10000 = 193.1.1.208/27
.
.
Host #27: 11000001.00000001.00000001.110 11011 = 193.1.1.219/27
Host #28:...

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