© 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 Hierarchical  Organized  Imagine a mechanic’s tools.  Envision these tools thrown into a big box. How much longer will it take to find a specific sized screwdriver or wrench in this mess? Much longer…  A flat network is like a messy toolbox. One large broadcast domain means that every device in the network receives each broadcast. Traffic delays and timeouts occur, which may slow the network to a crawl.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 4  In a single broadcast domain, or flat network, every device is in the same network and receives each broadcast. In small networks, a single broadcast domain is acceptable. A Flat IP Addressing Structure

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 5 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 6  As your network locations grow, you segment with routers. A Flat IP Addressing Structure Eventually, this growth becomes harder to organize

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 7 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 8 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 9 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 10 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 11 Activity – Are these the same network?

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 12 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 13 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 14 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 15 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 16 VLSM Example

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 17 Activity - How many hosts?

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 18 Now Do Another – Pick the Addresses

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 19 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 20 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 21 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 22 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 23 Activity – Route Summarization

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 24 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 25 Calculating Route Summarization

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 26 Discontiguous Networks Classful routing results in each router advertising the major Class C network without a subnet mask. As a result, the middle router receives advertisements about the same network from two different directions.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 27 Private IP Space and NAT  Using private addressing has these benefits: It alleviates the high cost associated with the purchase of public addresses for each host. It allows thousands of internal employees to use a few public addresses. It provides a level of security, because users from other networks or organizations cannot see the internal addresses.  RFC 1918 governs the use of the private address spacing. Class A: Class B: Class C:

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 28 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 29 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 30 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 31 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 32 Static NAT example

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 33 Dynamic NAT example

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 34 Using PAT

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 35 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 36