© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 1 Version 4.0 Addressing in an Enterprise Network Introducing Routing and Switching in the Enterprise – Chapter 4

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 2 Objectives  Analyze the features and benefits of a hierarchical IP addressing structure.  Plan and implement a VLSM IP addressing scheme.  Plan a network using classless routing and CIDR.  Configure and verify both static and dynamic NAT.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 3 Features & Benefits of a Hierarchical IP Addressing Structure  Flat networks with a single broadcast domain lose efficiency as hosts are added  Two solutions: Create VLANs Use routers in a hierarchical network design

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 4 Features & Benefits of a Hierarchical IP Addressing Structure  Classful network address in the Core Layer  Successively smaller subnets in the Distribution and Access Layers

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 5 Features & Benefits of a Hierarchical IP Addressing Structure Use subnetting to subdivide a network based on:  Physical location or logical grouping  Application and security requirements  Broadcast containment  Hierarchical network design

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 6 Plan / Implement a VLSM Addressing Scheme  Subnet mask: 32-bit value  Distinguishes between network and host bits  Can vary in length to accommodate number of hosts on LAN segment

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 7 Plan / Implement a VLSM Addressing Scheme  Boolean ANDing compares bits in host address to bits in subnet mask  1 and 1 = 1  1 or 0 and 0 = 0  Resulting value is network address

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 8 Plan / Implement a VLSM Addressing Scheme Steps in basic subnetting:  Borrow bits from the host side  Add them to the network side  Change mask to reflect additional bits

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 9 Plan / Implement a VLSM Addressing Scheme Elements of an addressing scheme:  Subnet number  Network address  Host range  Broadcast address

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 10 Plan / Implement a VLSM Addressing Scheme Benefits of Variable Length Subnet Masks (VLSM):  Flexibility  Efficient use of address space  Ability to use route summarization

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 11 Plan / Implement a VLSM Addressing Scheme  Apply masks from largest group to smallest  Avoid assigning addresses that are already allocated  Allow for some growth in numbers of hosts on each subnet

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 12 Plan a Network Using Classless Routing and CIDR Classful routing  Default subnet masks  Class determined by first octet  No subnet mask information exchanged in routing updates Classless routing  Network prefix  Slash (/) mask  Subnet mask information exchanged in routing updates

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 13 Plan a Network Using Classless Routing and CIDR  Classless Inter-Domain Routing (CIDR)  Uses address space efficiently  Used for network address aggregation or summarizing

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 14 Plan a Network Using Classless Routing and CIDR Route summarization:  Use single address to represent group of contiguous subnets  Occurs at network boundary  Smaller routing table, faster lookups

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 15 Plan a Network Using Classless Routing and CIDR  Discontiguous subnets cause unreliable routing  Avoid separating subnets with a different network

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 16 Plan a Network Using Classless Routing and CIDR  Use routing protocols that support VLSM  Plan subnetting to complement hierarchical design  Disable auto-summarization if necessary  Update router IOS  Allow for future growth

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 17 Configure and Verify Static and Dynamic NAT  RFC 1918: private IP address space  Routed internally, never on the Internet  “Hides” internal addresses from other networks

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 18 Configure and Verify Static and Dynamic NAT  Network Address Translation (NAT)  NAT translates internal private addresses into one or more public addresses  Use on boundary routers

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 19 Configure and Verify Static and Dynamic NAT  Static NAT: map single inside local address to single public address  Dynamic NAT: use a pool of public addresses to assign as needed

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 20 Configure and Verify Static and Dynamic NAT  Port Address Translation (PAT)  Dynamically translate multiple inside local addresses to one public address

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 21 Summary  Hierarchical network design groups users into subnets  VLSM enables different masks for each subnet  VLSM requires classless routing protocols  CIDR network addresses are determined by prefix length  Route summarization, route aggregation, or supernetting, is done on a boundary router  NAT translates private addresses into public addresses that route over the Internet  PAT translates multiple local addresses into a single public address

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 22