Intro to IP Address and CIDR

Host address all 0: NW address. Host address all 1: (directed) broadcast address.

A valid host IP address should not have all bits as 0s.

Loopback address: 127.x.x.x

Classes of IP address(RFC 791)

Class A

• 8 bit nw address (0....),
• 127 networks 2^7, 0-126
• 127 is loopback address.
• 16.7 million host 2^24 - 2,

Class B

• 16 bit nw address(10....),
• 2^14=16384 networks
• network address,. 128.0 to 191.255
• 65000 host 2^16-2

Class C

• 24 bit nw address(110.....),
• 192.0.0 to 223.225.225,
• 2^21=20,97,152 networks
• 254 host 2^8-2

Class D

• NW address (1110....)
• Multicast address
• Used in video streaming and broadcast applications.
• 224.0.0.0 to 239.255.255.255
• There is no distinction of public or private IP.

Class E

• NW address (1111...)
• Experimental address
• 240.0.0.0 to 255.255.255.255

Private IP address space(RFC 1918)

• Defines addresses which will be private to an organisation and will connect to internet via gateway.
• Class A: 10.0.0.0 to 10.255.255.255
• Class B: 172.16.0.0 to 172.31.255.255
• Class C: 192.168.0.0 to 198.168.255.255
• Private IP -> NAT-> Public IP
• NAT happen at gateway.

Subnetting:

• Routing happen in layer 3, network layer.
• Routing based on IP address.
• Network mask: to get network address from IP address.
• In class based IP addressing scheme, ne mask is defined by address class.
• In subnetting we manually specify subnet mask.

Why subnetting:

• Efficient use of IP address.
• Facilitate heirarchical network: subnets of subnets.
• Allows for address summarisation.

Subnet bits: borrowed from host address bits.

Questions to ask when subnetting:

• What is sub-network ID.
• What is usable host ID ranges.
• What is broadcast address.
• What is next sub-network ID.

Note:

• 1st host address= subnet Id + 1
• Last host= next sub-network Id -2
• Broadcast address= next sub-network Id - 1

Subnet increment: The value by which the next sub-network I'd increase. This value is the "binary weight" of last(lsb)subnet bit.

IP routing table:

• All the networks the router is connected to.
• All the networks the device has learnt from dynamic routing protocols like ospf, eigrp or static routes.

Powers of 2:

• 2^4 = 16
• 2^5 = 32
• 2^6 = 64
• 2^7 = 128
• 2^8 = 256