CIM 2465 IP Subnetting 1 IP Subnetting Textbook: Networking Basics, CCNA 1 Companion Guide, Cisco Press Cisco Networking Academy Program, CCNA 1 and 2, Companion Guide, Cisco Press, Latest Edition
Dec 19, 2015
CIM 2465 IP Subnetting 1
IP Subnetting
Textbook:
Networking Basics, CCNA 1 Companion Guide, Cisco Press
Cisco Networking Academy Program, CCNA 1 and 2, Companion Guide, Cisco Press, Latest Edition
CIM 2465 IP Subnetting 2
Brief Review
• Rules?
• Terms– Subnet– Subnet Number– Subnet Mask
CIM 2465 IP Subnetting 3
Determining the Number of Required Subnets and the Resulting Subnet Mask
• To come up with a subnetting plan (subnetting scheme), the engineer must answer the following questions:– How many subnets are required for a particular netwo
rk?– What is the largest number of hosts needed in the lar
gest subnet?– How many subnet bits does the subnet mask need to
support (at least) that many subnets?– How many host bits does the subnet mask need to su
pport (at least) that many hosts per subnet?– What subnet mask(s) support(s) the required number
of subnet and host bits?
CIM 2465 IP Subnetting 4
Number of Subnets and Hosts
CIM 2465 IP Subnetting 5
Number of Subnet and Host Bits
CIM 2465 IP Subnetting 6
How to find?
• Number of required subnet bits (in mask)– Find the number s such that 2S – 2 >= the
number of required subnets
• Number of required host bits (in mask)– Find the number h such that 2h – 2 >= the
number of required hosts
CIM 2465 IP Subnetting 7
Examples
Required Number of Subnets
Required Number of Hosts
Min Subnet bits needed
Min Host bits needed
200 200
5 15
12 3000
100 100
CIM 2465 IP Subnetting 8
Determine the Mask
Network Number of Subnet Bits
Number of Host Bits
Mask
128.1.0.0 8 8
192.168.9.0 3 5
172.31.0.0 4 12
130.10.0.0 7 7
CIM 2465 IP Subnetting 9
Determine Subnet Numbers and Assignable IP Addresses in Each Subnet
• Subnet number– The numerically lowest number in a subnet, represents a particul
ar IP subnet
• Subnet broadcast address– The highest numerical value in a subnet, for broadcast
• Assignable IP address– IP addresses that may be assigned to an interface
• Subnet zero (zero subnet)– The numerically smallest subnet number. With classful IP addres
sing, not be used
• Broadcast subnet– The numerically largest subnet number, With classful IP address
ing, not be used
CIM 2465 IP Subnetting 10
CIM 2465 IP Subnetting 11
Case
• Class C network: 192.168.9.0
• Mask: 255.255.255.224
CIM 2465 IP Subnetting 12
Finding Subnets
11000000 10101000 00001001 000 00000 192.168.9.0*
11000000 10101000 00001001 001 00000 192.168.9.32
11000000 10101000 00001001 111 00000 192.168.9.224*
CIM 2465 IP Subnetting 13
Finding Subnet Broadcast Address
11000000 10101000 00001001 000 11111 192.168.9.31*
11000000 10101000 00001001 001 11111 192.168.9.63
11000000 10101000 00001001 111 11111 192.168.9.255*
CIM 2465 IP Subnetting 14
Range of Valid Addresses
Subnet Lowest IP Highest IP Broadcast
192.168.9.0* 192.168.9.1 192.168.9.30 192.168.9.31
192.168.9.32 192.168.9.33 192.168.9.62 192.168.9.63
192.168.9.224*