ipv4-v6

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Why create a subnet mask?

Tells device which part of an address is

the network # including the subnet and

which part is the host

Filters the node IP address to determine

which subnet it belongs to

NETWORK/SUBNET/HOST

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How to Create Subnets

27 26 25 24 23 22 21 20128 64 32 16 8 4 2 1

1 0 0 0 0 0 0 0 128

1 1 0 0 0 0 0 0 1921 1 1 0 0 0 0 0 224

1 1 1 1 0 0 0 0 240

1 1 1 1 1 0 0 0 2481 1 1 1 1 1 0 0 252

1 1 1 1 1 1 1 0 254

1 1 1 1 1 1 1 1 255

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The class determines which part

of the address belongs to the

network and which part belongsto the host

Class ANNNNNNNN.hhhhhhhh.hhhhhhhh.hhhhhhhh

Class B

NNNNNNNN.NNNNNNNN.hhhhhhhh.hhhhhhhh

Class C

NNNNNNNN.NNNNNNNN.NNNNNNNN.hhhhhhhh

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IP Subnet addressing default

subnet masksIn Binary Form

Class A

11111111.00000000.00000000.00000000

Class B

11111111.11111111.00000000.00000000

Class C

11111111.11111111.11111111.00000000

Class A -

255.0.0.0

Class B -

255.255.0.0

Class C -

255.255.255.0

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Restrictions on subnets

Network addresses of all 0s in the host

portion are reserved for specifying the

network

Network addresses of all 1s in the host

portions are reserved for the broadcast

address

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How an IP address

Is Composed

Part of the 32Bits represents

A networkID

The remainder isUsed to represent

A host with thenetwork

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Network & Host IDs

Network ID Each network has a uniquenetwork number Each Network connected to the Internet has to

have a globally unique ID no other Internet-

connected network in the world can have the sameNetwork ID

Host ID Within a given network Host IDs are used to identify

hosts Hosts any device that needs to be addressed by an IP address

- computers, printers, routers, etc.

Host IDs must be unique within a given network.

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How Bits Are Set Up for Each IP

Address Class

Note

This shows thebinary values inthe first 3 bits ofthe 3 classes:0?? For class A

10? For class B110 for class C

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How Address Classes

Affect a Network

0 0 0 0 0 0 0 1

1 0 0 0 0 0 0 0

1 1 0 0 0 0 0 0

0 1 1 1 1 1 1 0

1 0 1 1 1 1 1 1

1 1 0 1 1 1 1 1

Ranges of 1st octet network IDs

A

B

C

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private address cannotbe routed on the internet

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IP Address Guidelines

First Octet Network ID Rules Network ID cannot be 127.

ID bits cannot be all 1s.

ID bits cannot be all 0s.

For class B or C Network IDs

Second octet (and the third octet for class C

networks) can be any number from 1 -255, or

00000000 to 11111111

Class B: 131.0.x.x or 131.255.x.x are OK

Class C: 200.0.0.x or 200.255.255.x or

200.255.0 are all OK

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IP Address Guidelines

First Octet Network ID Rules Network ID cannot be 127.

ID bits cannot be all 1s.

ID bits cannot be all 0s. For class B or C Network IDs

Second octet (and the third octet for class Cnetworks) can be any number from 1 -255, or

00000000 to 11111111 Class B: 131.0.x.x or 131.255.x.x are OK

Class C: 200.0.0.x or 200.255.255.x or

200.255.0 are all OK

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Problems with default masks

They only provide for a single network segment Class C 255.255.255.0 allows for a maximum of 254 hosts on the

segment

Class B 255.255.0.0 allows for a maximum of 65,534 hosts on thesegment

Class C 255.0.0.0 allows for a maximum of 16,777,214 hosts onthe segment

Beyond class C networks, current LAN technologies will not supportanywhere near the maximum number of hosts/segment

Since there is only 1 network segment: Difficult to use different topologies in the LAN (Ethernet, FDDI,

Token Ring)

Difficult to have a geographically dispersed LAN connected using aWAN technology.

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Common masks Masks

255.255.252.0 /22 1024 hosts

255.255.254.0 /23 512 hosts

255.255.255.0 0 /24 256 hosts

255.255.255.128 0 + 128 /25 128 hosts

255.255.255.192 128 + 64 /26 64 hosts

255.255.255.224 192 + 32 /27 32 hosts

255.255.255.240 224 + 16 /28 16 hosts

255.255.255.248 240 + 8 /29 8 hosts255.255.255.252 248 + 4 /30 4 hosts

255.255.255.254 252 + 2 /31 not usable

255.255.255.255 254 + 1 /32 single host

Learn or memorize them.

Or, use the addition trick in column 2

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Subnetting IP Addresses

Variable length subnet masks

Could subnet a class B into several chunks

Network Host

Network HostSubnet

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0Subnet

Mask

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Problem #1: Lifetime of

Address Space Example: an organization needs 500

addresses.

A single class C address not enough (256

hosts).

Instead a class B address is allocated.

(~64K hosts) Thats overkill -a huge

waste.

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IPv4 Addressing

Dotted Decimal Notation

Dotted Decimal Notation Four bytes (8 bits = 1 byte) per address

Each byte separated by a dot

Each byte expressed in decimal notation Example:

Dotted Decimal Notation: 192.16.224.254

Binary Notation?:

What is the minimum decimal value any byte can be

assigned? What is the maximum decimal value any byte can be

assigned?