IP Addressing Scheme

Types of IP Addressing

• 1. Classful Addressing. Ancient
  • Valid IPv4 Addresses
• 2. Classless Addressing
  • Subnet Mask / Prefix / Netmask
    • CIDR(Classless Interdomain Routing) Notation
    • Classes(A,B,C) & their Subnet masks
    • Valid Subnet masks
  • Network ID / Network Address
  • Broadcast Address
  • Finding Network,Broadcast Address using Prefix

Subnetting

Supernetting /Prefix Aggregation/ Route Aggregation/ Route Summarization

Address Types

• A. Private IP Addresses
  • Inside Local IP Address
  • Inside Global IP Address
• B. Outside Network
  • Inside Global Address
  • Outside Global Address
• C. Reserved and Documentation Addresses
  • Carrier-grade NAT

IPV4 Addressing Scheme

• This is used to identify Host and network part from an IP address.
• All hosts on same N/W have same N/W-ID. Same network means these hosts can communicate with each other without any router. They are on same LAN.

Types of IP Addressing

1. Classful Addressing

• Each IP Address is assigned to a class.
• class A, B addresses are exhausted. Class C addresses are given to new organizations

      Class        A                       B                   C                D(MULTICAST)      E(experimental)
      N/W part       a                       a.b                 a.b.c            NA                 NA
      Host part      b.c.d                   c.d                 d                NA                 NA
      Range          0-127.x.x.x             128-191.x.x.x       192-223.x.x.x    224-239.x.x.x      240-255.x.x.x     
      No of hosts    2pow24=1677716-2        2pow16=65536-2      2pow8=256-2      NA                 NA
                    N/W-ID,broadcast removed
      Start Bits      0                      10                  110             1110                1111
      Start Address   0.0.0.0                128.0.0.0           192.0.0.0       224.0.0.0           240.0.0.0
      End Address     127.255.255.255        191.255.255.255     223.255.255.255 239.255.255.255     255.255.255.255
      Suitable For    Large Org              Medium Org          Small Org
      
      

Valid IPv4 Addresses

• First and last address in any network or subnet can't be assigned to any individual host. Eg: 192.168.123.0 and 192.168.123.255
• 0 address is invalid bcoz it's specifies a network not host. 192.168.123.0 is N/W not host
• 255 address is invalid bcoz it's used to broadcast a message to every host on a network. 192.168.123.255 is broadcast address

      
      0.0.0.0 Invalid Address(N/W ID)
      255.255.255.255 - Broadcast Address
      
      

2. Classless Addressing

• No portion for n/w & hosts is separated. Subnet mask/netmask is used to get n/w and host parts.
• Subnet mask decides how many hosts are possible on a network.

Subnet Mask / Prefix / Netmask

Number of ON bits in 32 bit address going from left to right defines n/w address. 1's defines network and 0's defines host.

      <---1's defines n/w   ---> <-host->
      11111111.11111111.11111111.00000000    =   255.255.255.0   
      
      

CIDR(Classless Interdomain Routing) Notation

Representation in which address is written with a suffix indicating the number of on bits in the subnet mask

      11111111.11111111.11111111.00000000    =   255.255.255.0   =    /24   called CIDR notation
      
      

Classes & their Subnet masks

      Class                 A                 B                 C                 D       E
      Possible Hosts      2pow24            2pow16            2pow8               NA      NA
      Subnet mask       255.0.0.0(/8)   255.255.0.0(/16)    255.255.255.0(/24)
      Network part      1st 8 bits        1st 16 bits         1st 24 bits
      
      

Valid Subnet masks

Only contiguous subnet masks are valid. ie Contiguous 1's from left.

      Invalid: 255.255.255.1   = 11111111.11111111.11111111.00000001   //Not contiguous
      Valid:   255.255.255.128 = 11111111.11111111.11111111.1000000
      
      

Why gaps in subnet mask not valid?
- Impossible for a router to accurately summarize and aggregate prefix ranges.

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