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