© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Constructing Network Addresses Constructing a Network Addressing Scheme

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Outline Overview Subnetworks Computing Useable Subnetworks and Hosts Summary Lab Exercise 5-3: Computing Useable Subnetworks and Hosts

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Flat Topology Problems All devices share the same bandwidth. All devices share the same broadcast domain. It is difficult to apply security policy.

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Subnetworks Smaller networks are easier to manage. Overall traffic is reduced. You can more easily apply network security policies.

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v IP Address Bit Review Remember: One address is reserved as the network ID. One address is reserved as broadcast address. Available number of host addresses = 2 h – 2 where h is the number of significant bits in the host ID.

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Number of Subnets Available To identify subnets, you will borrow bits from the host ID portion of the IP address Number of subnets available depends on the number of bits borrowed. One address is still reserved as the network address. One address is still reserved as broadcast address. Available number of subnets = 2 s where s is the number of bits borrowed.

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Possible Subnets and Hosts for a Class C Network

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Possible Subnets and Hosts for a Class B Network

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Possible Subnets and Hosts for a Class A Network

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Summary Networks, particularly large ones, are often divided into smaller subnetworks or subnets. Subnets can improve network performance and control. A subnet address extends the network portion, and is created by borrowing bits from the original host portion and designating them as the subnet field. Determining the optimal number of subnets and hosts depends on the type of network and the number of host addresses required. The algorithm for computing a number of subnets is 2 s, where s is the number of subnet bits.

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v