modul_04_subneting ipv4

8/8/2019 Modul_04_Subneting IPv4

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Layer 3 Devices

Routers

Interconnect network segments or entirenetworks.

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.

Determines best path for data on an internetwork.

A.K.A Layer 3 Switching



Path Determination

The process the router uses to choose the next hop

in the path the packet travels.

The router uses the network address to identify thedestination network of a packet within an

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internetwork. IP addresses can be assigned by a network

administrator or automatically (dynamically.)



Layer 3 Packet/Datagram

VERS HLEN Service Type Total Length

4

Time to Live Protocol Header Checksum

Source IP Address

Destination IP AddressIP Options (if any) Padding

Data



Network Layer Addresses

Network layer addresses are 32 bits long.

They are represented as four octets in dotted

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233.14.17.0ec ma ormat.

The IP address has two components:

The Network ID

The Host Id



Layer 3 Addresses

Network ID

Assigned by ARIN(www.arin.net)

Identifies the network to

Host ID

Assigned by a networkadministrator.

Identifies the specific

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w c a ev ce sattached.

May be identified by one,two, or three of the first

three octets.

ev ce on a ne wor .

May be identified by one,two, or three of the lastthree octets.



IP Addresses

32 bit address represented as 8 bit dotted decimals.

Different class addresses reserve different amounts of

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.

Class A N H H H

Class B N N H H

Class C N N N H



Number of Hosts

Maximum number of hosts vary for each class.

Class A has 16,777,214 available hosts (224 –2)

Class B has 65,534 available hosts (216 –2)

Class C has 254 available hosts (28 –2)

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The first address in each network is reserved for thenetwork address and the last address is reserved for

the broadcast address.



Classes

How do you know what class an IP address

is in?

If the first octet is between:

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– s a c ass a ress 128-191 it is a class B address

192 – 223 it is a class C address



Recognizing Class in Binary

Format

128s place 64s place 32s place

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Class B 1 0

Class C 1 1 0

Initial bitpattern infirst octet

of IPaddress.



Reserved Addresses

Broadcast Address – is used to send data to all of

the devices on a network. Broadcast IP addresses end with binary 1s in the

host part of the address.

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Class B Broadcast Address example: 176.10.255.255

(Remember decimal 255 = binary 11111111)



Basics of Subnetting

Subnetworks are smaller divisions of

networks.

They provide addressing flexibility.

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. . . su nets Subnet addresses are assigned locally,

usually by a network administrator.

Subnets reduce a broadcast domain.



Subnet Addresses

Include Class A, B, or C network portion plus

a subnet field and a host field. Bits are borrowed from the host field and are

desi nated as the subnet field.

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Network Subnet Host



How many bits can I borrow?

Size of Host Field Maximum # of borrowed bits

The minimum number of bits you can borrow is two.

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Class A24 22

Class B 16 14

Class C 8 6



Default Subnet Masks

Class A 255.0.0.0

16

Class B 255.255.0.0

Class C 255.255.255.0



Calculating a Subnet

We will subnet the IP address:

223.14.17.0

What class IP address is this?

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ass



Step #1

Determine the default subnet mask

Class C default subnet mask:

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255.255.255.0



Step #2

Determine the number of subnets needed

and hosts on each to determine how manybits to borrow from the host ID.

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13 subnets

10 hosts on each subnet



Step #3

Figure the actual number of subnets and

hosts by borrowing bits from host ID.

Let’s see how many subnets and hosts we

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.



Step #3 continued…

223.14.17.0

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X X X X H H H H

16 possiblesubnets

16 possiblehosts for each

subnet




We get 16 possible subnets and 16 possible hosts for each subnet because:

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leaving you with 24 or 16 possible combinations.

The same goes for the 4 leftover host bits.

Important: There are only 14 available subnets and hosts on each subnet. Why?




Because you cannot use the first and last

subnet.

Because you cannot use the first and last

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.

For each, one is the broadcast address andone is the network address.



Step #4

Determine the subnet mask.

223.14.17.0

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X X X X H H H H

Where X represents the borrowed bits forsubnetting.




Add the place values of X together to get the

last octet decimal value of the subnet mask.

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128 + 64 + 32 + 16 = 240

The subnet mask is: 255.255.255.240

The subnet mask is used to reveal thesubnet and host address fields in IP

addresses.



Step 5

Determine the ranges of host addresses for

each subnet.

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Step 5 continued…

Subnet # Subnet Bits Host Bits In Decimal1 0000 0000-1111 .0 -.15

2 0001 0000-1111 .16 - .31

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- . - .

4 0011 0000-1111 .48 - .63

5 0100 0000-1111 .64 - .79

6 0101 0000-1111 .80 - .95

7 0110 0000-1111 .96 - .111

8 0111 0000-1111 .112 - .127



Step 5 continued…

Subnet # Subnet Bits Host Bits In Decimal9 1000 0000-1111 .128 -.143

10 1001 0000-1111 .144 - .159

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- . - .

12 1011 0000-1111 .176 - .191

13 1100 0000-1111 .192 - .207

14 1101 0000-1111 .208 - .223

15 1110 0000-1111 .224 - .239

16 1111 0000-1111 .240 - .255



Step 5 continued…

There are 16 possible subnets.

There are 16 possible hosts on each subnet.

That equals 256 possible hosts.

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What are our available subnets? What are our available hosts on each

subnet? Why?????



Figuring Subnet

Network Addresses

Step #1: Change the IP host address to

binary. Step #2: Change the subnet mask to binary.

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combine the two. Step #4:Convert the network binary address

to dotted decimal.



Figuring Subnet

Network Addresses

IP Host 172.16.2.120Subnet Mask 255.255.255.0

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. . .

11111111.11111111.11111111.00000000

10101100.00010000.00000010.00000000

172.16.2.0

This is the subnet network address. It is the lowestnumbered address on the subnet network. It can help

determine path.

AND

modul_04_subneting ipv4

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