3.pptx

Subnetting an IPv4 Network Network Segmentation  Broadcast Domains  Broadcast Domains  Problems with Large Broadcast Domains • Slow network operations due to the significant amount of broadcast traffic. • Slow device operations because a device must accept and process each broadcast packet. ...

Subnetting an IPv4 Network Network Segmentation  Broadcast Domains  Broadcast Domains  Problems with Large Broadcast Domains • Slow network operations due to the significant amount of broadcast traffic. • Slow device operations because a device must accept and process each broadcast packet.  Reasons for Subnetting • Solution: reduce the size of the network to create smaller broadcast domains. • Because each broadcast domain connects to a different router interface, each domain needs its own network address space. • The process of breaking an address range into smaller address spaces is called subnetting. • Network administrators can group devices into subnets that are determined by location, organizational unit or device type. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 1 Subnetting an IPv4 Network Subnetting an IPv4 Network  Octet Boundaries • Subnets can be created based on octet boundaries. (/8, /16 or /24)  Subnetting on the Octet Boundary • Also known as IPv4 Classes. • Uses the octet boundaries to separate network from hosts.  Classless Subnetting • Uses address bits to separate network from hosts. • Allows for much more flexibility.  Classless Subnetting Example Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 2 Subnetting an IPv4 Network Subnetting an IPv4 Network (Cont.)  Creating 2 Subnets • A subnet mask of /25 applied to 192.168.10.0, creates two equal subnets, each one with 126 hosts.  Subnetting Formulas • • • • Use 2n, to calculate the number of subnets. Use 2h-2 to calculate the number of hosts. n is the number allocated to the network portion of the address. h is the number allocated to the host portion of the address.  Creating 4 Subnets • A subnet mask of /26 applied to 192.168.10.0, creates four equal subnets, each one with 62 hosts. • n = 2 and therefore 22 = 4. • h = 6 and therefore 26-2 = 62. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 3 Subnetting an IPv4 Network Creating 4 Subnets A subnet mask of /26 applied to 192.168.10.0, creates four equal subnets, each one with 62 hosts. n = 2 and therefore 22 = 4. h = 6 and therefore 26-2 = 62. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 4 n = 2 and therefore 22 = 4. h = 6 and therefore 26-2 = 62.  Creating Subnets with a /16 Prefix • A subnet mask of /16 applied to 172.16.32.0, creates a network with 65534 hosts. • A subnet mask of /18 applied to 172.16.32.0, creates 4 networks with 16382 hosts in each network. • A subnet mask of /22 applied to 172.16.32.0, creates 64 networks with 1022 hosts in each network.  Creating 100 Subnets with a /16 Prefix • A subnet mask of /23 applied to 172.16.32.0, creates 128 networks with 510 hosts in each network  Calculating the Hosts • Use 2h-2 to calculate the number of hosts. • h is the number allocated to the host portion of the address.  Creating 1000 Subnets with a /8 Prefix • A subnet mask of /18 applied to 20.0.0.0, creates 1024 networks with 16382 hosts in each network Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 5 Subnetting an IPv4 Network Subnetting to Meet Requirements  Subnetting Based on Host Requirements • Two considerations when planning subnets: • The number of host addresses required for each network. • The number of individual subnets needed.  Subnetting Based on Network Requirements • Administrators may be asked to subnet an IP range to accommodate a specific number of networks. • Think of a company with 7 departments where each department must have its own subnetwork. • The number of hosts per subnet, while secondary, is also important.  Network Requirement Example • • • • Assume the range 200.42.98.0/24 was given to the administrator. 7 subnets must be created. Each department will have no more than 29 hosts. A subnet mask of /27 applied to 200.42.98.0/24, creates 8 networks with 30 hosts in each network. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 6 Subnetting an IPv4 Network Benefits of Variable Length Subnet Masking  Traditional Subnetting Wastes Addresses • Subnetting based on classes is not very flexible. • Results in wasted addresses.  Variable Length Subnet Masks • By varying the mask, an administrator has more control. • Less waste.  Basic VLSM • A subnet mask of /30 applied to 200.42.98.0, creates a network with 2 hosts in each network. • The network 200.42.98.0/30 would be a perfect match for a serial link.  VLSM in Practice • Consider two routers connected by a Serial link: • RouterA would be 200.42.98.1/30 and RouterB would be 200.42.98.2/30. • 200.42.98.0/30 is the network address and 200.42.98.3/30 is the broadcast address. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 7 8.2 Addressing Schemes Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 8 Addressing Schemes Structured Design  Network Address Planning • Planning requires decisions on each subnet in terms of size, the number of hosts per subnet and how host addresses will be assigned.  Planning to Address the Network • The Primary Planning Considerations are: • Prevent Duplication of Addresses • Monitor Security and Performance • Provide and Control Access  Assigning Addresses to Devices • Different devices needs may also impact the addressing scheme. • Common devices are: • End user devices, servers, printers, network devices and gateways Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 9 8.3 Design Considerations for IPv6 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 10 Addressing Schemes Structured Design  The IPv6 Global Unicast Address • The IPv6 global unicast address normally consists of a /48 global routing prefix, a 16 bit subnet ID, and a 64 bit interface ID.  Subnetting Using Subnet ID • The subnet ID provides plenty subnets and host support in one subnet. • The subnet ID alone allows for creating up to 65,536 /64 subnets.  IPv6 Subnet Allocation • Address waste is not a concern in IPv6. • Administrators can concentrate on designing a logical scheme to address the network. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 11