Unit 24 Network Design IP Addressing (Part 3)

Objectives to date… Classes of IP addresses (A, B and C) Using Subnetting and Subnet Masks The Limitations of Classful IP addressing Classless Inter-Domain Routing (CIDR)

Objectives to date… CIDR – classless inter domain routing Having IP addresses with a ‘prefix’ /20 Identifying the Network ID, Host ID Calculating the number of hosts available on a subnet (2^12) = 4096 (2^12)-2 = 4094 Why? Calculating the Subnet Mask

Objectives for today… To determine from the CIDR IP Address the IP address range we can use (the first and last IP addresses, and therefore all combinations in between) To use the CIDR address for subnetting To determine the IP addresses that can be allocated for each subnet To use the Classful and Classless IP addressing for Task 2 Logical topology diagrams

CIDR – Valid Host Addresses Once you have found the network ID, subnet mask and have calculated the number of hosts/machines, according to the CIDR ‘prefix’, you now need to identify all IP addresses valid for this network. Look again at the table identifying the binary network ID, host ID and subnet mask…

CIDR: Network ID, Host ID, Subnet Mask Decimal /20 Binary Network ID Host ID Subnet Mask bits 12 bits

CIDR – Valid Host Addresses From the binary IP address (network ID) how do we identify the valid IP address range, i.e. the actual IP addresses that can be allocated to hosts given the IP address of /20?

CIDR – Valid Host Addresses Decimal /20 Network ID First Valid IP address Decimal IP address Last Valid IP address Decimal IP address The binary address cannot contain all zeros – the last bit is therefore a 1 The binary address cannot contain all ones – the last bit is therefore a 0

Exercises… Log onto the shared area Emerson A\Unit 24\IP Addressing\Week 3\CIDR Exercises part 2 Complete question 5a

Subnetting using CIDR When subnetting using CIDR you need to consider a few factors How many subnets do you need? How many devices (hosts) on each subnet? Do you need to plan for expansion in the future?

Subnetting using CIDR Here’s our Network ID in binary How many subnets? 4 in this example How many bits will I need to use if I need 4 subnets? 2^2=4 (There are only 4 possible combinations if I use 2 bits) bits

Subnetting: Subnet Last IP Address First IP Address Network ID 20 bits for the network 2 Subnet bits 10 Host bits

Subnetting: Subnet 2 Network ID First IP Address Last IP Address bits for the network 2 Subnet bits 10 Host bits

Subnetting: Subnet 3 Network ID First IP Address Last IP Address bits for the network 2 Subnet bits 10 Host bits

Subnetting: Subnet 4 Network ID First IP Address Last IP Address bits for the network 2 Subnet bits 10 Host bits

Exercises… Log onto the shared area Emerson A\Unit 24\IP Addressing\Week 3\CIDR Exercises part 2 Complete question 5b and question 6 Show all binary working out