Protocol

TCP/IP (Transmission Control Protocol/Internet Protocol)

IP

1. IP Address is a 32-bits long and is composed of four 8-bits * octets.
2. Each IP Address defined into the Network ID and Host ID.

* Remark: from 0-255 (00000000₂ to 11111111₂ )

Class A

Network ID

• * 00000001 to 01111110
• so there's 126 networks in class A

Host ID

• Host ID bits can't be all 0, otherwise it's represent "this Network".
• Host ID bits can't be all 1, otherwise it's represent broadcast.
• So there's 2²⁴ - 2 =16,777,214 host in a class A network.

* Remark: 127 is reserved (預留) for loopback and diagnostic (診斷) functions.

• e.g. 127.0.0.1 (localhost) used to diagnostic TCP/IP.

Class B

Network ID

• * 10000000 to 10111111 (191-128=63 [00111111])
• so there's 2¹⁴ = 16384 networks in class B

Host ID

• Host ID bits can't be all 0, otherwise it's represent "this Network".
• Host ID bits can't be all 1, otherwise it's represent broadcast.
• So there's 2¹⁶ - 2 =65534  host in a class B network.

Class C

Network ID

• * 11000000 to 11011111 (223-192 = 31 [ 00011111 ])
• so there's 2²¹ = 2,097,152 networks in class C

Host ID

• Host ID bits can't be all 0, otherwise it's represent "this Network".
• Host ID bits can't be all 1, otherwise it's represent broadcast.
• So there's 2⁸ - 2 =253  host in a class C network.

Class D

224.0.0.0 to 239.255.255.255 is used for multicast packets to send to a group of hosts.

e.g. WINS server use multicast packets to call WINS clients.

Class E

240.0.0.0 to 255.255.255.254 is reserved for future use.

* Remark: 255.255.255.255 represent to broadcast.

Subnet Mask

Subnet mask is used to identify the source IP and the destination IP belong to local network or remote network,
so IP Address must work with subnet mask.

e.g.1

A

----------------------->

B

So Computer A and Computer B is located in same network (local network), the packets can sent directly.

e.g.2

A

----------------------->

B

So Computer A and Computer B is located in remote network, the packets is sent to default gateway (Router).

Subnetting Network

Subnetting network means to dividing a network into multiple smaller network.

* the subnet bits cannot be all 0 or all 1.

* subnet bits 由頭取出, 不能分開.

e.g.1

## when using 224 as subnetting, we can have 6 subnet:

e.g.2

A

----------------------->

B

So Computer A and Computer B is located in remote network, the packets is sent to default gateway (Router).

Computer A is belongs to 128.32.0.0 network, host ID= 8.32.2

Computer B is belongs to 128.192.0.0 network, host ID= 4.32.3

e.g.3

A

----------------------->

B

So Computer A and Computer B is located in remote network, the packets is sent to default gateway (Router).

Computer A is belongs to 200.200.100.96 network, host ID= 4

Computer B is belongs to 200.200.100.128 network, host ID = 2

Supernetting Network

Also called CIDR (Classless InterDomain Routing)

Supernetting is used to combine some small network into a lager network.

e.g.

Your company has been assigned 8 class C network.

Seen in binary, we notice that the first five bits is same, hence, we can use the supernet mask:

255.255.248.0=11111111.11111111.11111000.00000000