IP Subnetting (Week 4, Wednesday 1/31/2007) © Abdou Illia, Spring 2007

2 Structure of IP addresses Network Part (n) Local Part (h) Class Annnnnnnn.hhhhhhhh.hhhhhhhh.hhhhhhhh – Class Bnnnnnnnn.nnnnnnnn.hhhhhhhh.hhhhhhhh – Class Cnnnnnnnn.nnnnnnnn.nnnnnnnn.hhhhhhhh – Sgmt. partHost part

3 Reserved IP addresses ClassRange A – B – C – IP addresses reserved for private use. AddressUse Example: Local broadcast to LAN computers Broadcast to network / Loopback address (for self addressing) Prohibited x.xAutomatic Private IP Addressing Special IP addresses.

4 Structure of IP addresses The division between Network part, Segment part, and Host part is determined by a computer or a router by using a network mask. Network Part Segment Part Host Part

5 Network mask A 32 bit number, just like an IP address, where all bits in the Network Part and the Segment Part are set to 1, and all bits in the Host Part are set to 0. Example: (or in decimal notation) Computers use Network mask, along with the IP address, to determine whether or not a destination IP address is on the same logical network.

6 Two Virtual LANs Switch

7 Two interconnected LANs

8 The ADDing technique Are the following three Class C IP addresses from the same network? , and IP: Mask: Network: /24 IP: Mask: Network: /24 IP: Mask: Network: / Network 1: /24, i.e network starting at with network mask Network 2: /24, i.e network starting at with network mask

9 Subnetting a class C network Suppose the /24 network You want to divide that network into two segments  You can decide to use the first bit of the fourth octet as dividing point between your network segments. So, your network mask would be: And you will have about 2 7 = 128 hosts in each segment Segment 1: to Segment 2: to How to determine the two segments using the ADDing technique?

10 Subnetting a class C network IP: Mask: Network: / IP: Mask: Network: / Segment 1: to

11 Subnetting a class C network IP: Mask: Network: / IP: Mask: Network: / Segment 2: to

12 Question 1 Network A is IP network x/24 (i.e a Class C network with a default 24-bit mask). Using the IP Subnet Calculator, determine the maximum number of hosts (computers) in each of the Network A’s subnets assuming that there are two subnets. You answer: ________. Using the IP Subnet Calculator, determine the maximum number of subnets for a Class B network assuming that the four first bits of the third octet in each IP address are used as subnet bits. Your answer: _____. What is the maximum number of computers for each subnet? Your answer: ______.

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