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Ccna ppt Ccna ppt Presentation Transcript

  •  In sub netting, a network is divided into smaller sub networks with each subnet having its own subnet address
  •  Dividing the barrel of apples into small barrels or baskets does not give us any more apples… 33 33 33
  • 97 Apples (99– 2) Before sub netting: In any network (or subnet) we can not use all the IP addresses for host addresses. We lose two addresses for every network or subnet. 1. Network Address - One address is reserved to that of the network. 2. Broadcast Address – One address is reserved to address all hosts in that network or subnet.
  • Two parts of IP address 1. Net ID 2. Host ID  To reach a host, we must first reach the network using net id, then using host id to reach the host. 
  •  The 5 IP classes are split up based on the value in the 1st octet:
  • Sometimes two level hierarchy is not enough. For example: An organization with a class B address. The organization has two levels hierarchical addressing, but it cannot have more than one physical network.  • • The host cannot be grouped, and all of the host has the same level Solution  sub netting
  • • In the above example,  The rest of the internet is not aware that the network is divided into three physical subnet.  A packet destined for host still reaches router R1. The destination address of the IP datagram is still a class B where • 141.14 defines the net id • And 2.21 defines the host  However, when the datagram arrives a router R1, the interpretation of the IP address changes. • R1 knows the network 141.14 physically divided into three subnets. • It knows that the last two octets define two things: subnet id and host id ( 2.21  subnet id 2 and host id 21) • Router uses first two octets as net id, the third subnet id, and the fourth host id
  •  A class A address:    Is made of a one-byte net id and a three-byte host id Can have one single physical network with up to 16,777,214 (224-2) users. If we want more physical networks, we can divide this one range into several smaller ranges
  •  A class B:    Is made A two byte net id and two-byte host id Can have one single physical network and up to (216-2)=65,534 hosts on the network. If we want more physical network, we can divide this one big range into several smaller ranges.
  •  A class C address:    is made of a three byte net id and one-byte host id Can have one single physical network and up to 254 (28 – 2) host on that network If we want more physical network, we can divide this one range into several smaller range.
  •   The internet allows a site to use variable-length sub netting. For an example of when this may be desirable, consider a site that is granted a class C address and needs to have five subnets with the following of host: 60,60,60,30,30 This site can not use a subnet mask with only two bits in the subnets section because this allows only four subnet with 62 hosts ( 256/4 - 2 = 62).  Nor can the site use a subnet mask with three bits in the subnet section, because this allows 8 subnets with 30 hosts (256/8 -2 = 30)  Solution for the problem: variable length subnetting.   The router uses two different masks, one applied after the other  First mask uses the mask with 26 1s (11111111 11111111 11111111 1100000 or to divide the network into four subnets  Then it applies the second mask with 27 1s ( to one of the subnets to divide it into two smaller subnets
  •  An IP address has 2 parts:     The Network identification. The Host identification. Frequently, the Network & Host portions of the address need to be separately extracted. In most cases, if you know the address class, it’s easy to separate the 2 portions.
  •  There are default standard subnet masks for Class A, B and C addresses