Definition

32 bits in length writen in 4 fields of 8 bit each separated by a dot “.”

All IP addresses in the same group must not be separated from each other by a router.

IP addresses separated from each other by a router must be in different groups.

IPv4 Header

Octets

x.x.x.x = len(x) * 4 = 32 Bits

X is called octet. Each octet consists of 8 bits.

Classful IP addressing

Used when IP addressing was brand new, it was broken down into classes. Nowadays IP addresses are not broken down classfully, but classlessly ().

Class	Value of 1st octet	Subnet mask		Example
A	1-126	255.0.0.0	/8	10.10.10.10/8
B	128-191	255.255.0.0	/16	150.101.45.45/16
C	192-223	255.255.255.0	/24	200.0.0.30/24
D	224-239	-	multicasting	-
E	240-255	-	Experimental	-

Multicast

A magazine subscription The hosts have to subscribe to the “master”

127.0.0.0

Reserved for experimental purposes

Structure of the IP

A subnet mask separates a host address from the network address.

Convert IP addr to binary

Class C address

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IP = 200.10.10.10 –> First octet is 200 / Network mask: 255.255.255.0

2^7	2^6	2^5	2^4	2^3	2^2	2^1	2^0
128	64	32	16	8	4	2	1
1	1	0	0	1	0	0	0

because:

1*128 + 1*64 + 0*32 + 0*16 + 1*8 + 0*4 + 0*2 + 0*1 = 200

Class B address

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IP = 150.100.10.10 / Network address: 255.255.0.0

Network adress: 150.100.0.0/16

Broadcast address: 150.100.255.255

Last valid IP address: 150.100.255.254

Number of available address: 2^n - 2, where n = 16 because 16 bits of host address

Naming conventions

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200.10.10.0/24 –> Network address

200.10.10.255 –> Broadcast address

Number of available IP address

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For previous example it is: 200.10.10.1 - 200.10.10.254

Formula: 2^n - 2, where n = host bits (-2 because you cannot use the first and the last address)

Routing theory

Routing

Layer 3 function The process of going from one broadcast domain to another broadcast domain (both Layer 3 domains)

When H1 sends an ARP broadcast message, r1 will act as a proxy Arp responding with its own MAC address (on f0/0).