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Addressing in an Enterprise Network

Addressing in an Enterprise Network. Introducing Routing and Switching in the Enterprise – Chapter 4. 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.

matthew-weiss
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Addressing in an Enterprise Network

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  1. Addressing in an Enterprise Network Introducing Routing and Switching in the Enterprise– Chapter 4

  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.

  3. Features & Benefits of a Hierarchical IP Addressing Structure • Flat networks • single broadcast domain • lose efficiency as hosts are added, increase traffic delays, wastes bandwidth • All hosts can be reached without passing through a router • Two solutions: • Create VLANs • Use routers in a hierarchical network design

  4. Features & Benefits of a Hierarchical IP Addressing Structure • Use routers in a hierarchical network design • network is divided into layers to reduce congestion • Reduces size of failure domains • logically groups networks into smaller subnetworks • Can simplify network management and improve scalability

  5. Features & Benefits of a Hierarchical IP Addressing Structure • Classful network address in the Core Layer • Successively smaller subnets in the Distribution and Access Layers

  6. 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

  7. Why VLSM?? • IP was in trouble • Running out of address space • Wasting addresses by assigning class B when C wasn’t big enough • Fix to IPv4 • Viewed as a stop-gap measure until release if IPv6 • So successful that IPv6 implementation has been effectively postponed

  8. 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 • Benefits of VLSM • Allows efficient use of address space • Supports hierarchical addressing capability

  9. 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

  10. 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

  11. Plan / Implement a VLSM Addressing Scheme 192.168.100.130/27 What is the default subnet mask? 255.255.255.0 What is a /27 subnet mask? 255.255.255.224 What is the network address of this host? 192.168.100.128 What is the broadcast address of this host? 192.168.100.159

  12. Plan / Implement a VLSM Addressing Scheme 192.168.2.93/29 How many bits were borrowed? 5 What is the default subnet mask? 255.255.255.0 What is a /29 subnet mask? 255.255.255.248 What is the network address of this host? 192.168.2.88 What is the broadcast address of this host? 192.168.2.95

  13. Plan / Implement a VLSM Addressing Scheme 10.118.197.55/20 What is the default subnet mask? 255.0.0.0 What is a /20 subnet mask? 255.255.240.0 How many bits were borrowed? 12 bits How many hosts will this accommodate? 2 to the 12

  14. Plan / Implement a VLSM Addressing Scheme Elements of an addressing scheme: • Subnet number • Network address • Host range • Broadcast address

  15. Plan / Implement a VLSM Addressing Scheme Benefits of Variable Length Subnet Masks (VLSM): different subnet mask by each department • Flexibility—accommodates different size groups • --Logically groups members into smaller subnetworks • Efficient use of address space • Ability to use route summarization • Simplifies network management • Improves scalability

  16. 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

  17. Classful routing Default subnet masks Class determined by first octet No subnet mask information exchanged in routing updates (because it is using the default) Updates received by a router in a different major network have the default mask applied Plan Network Using Classless Routing & CIDR Classless routing • Network prefix • Slash (/) mask • Subnet mask information exchanged in routing updates • Can use a /30 for serials so you don’t waste addresses

  18. Plan a Network Using Classless Routing and CIDR • Classless Inter-Domain Routing (CIDR) • Uses address space efficiently • Used for network address aggregation or summarizing • Reduces routing table size • Reduced routing update traffic

  19. VLSM SERIAL LINKS • Use /30 (so you don’t waste space) • Be sure to use numbers already being used 1 192 128 63 128 64 127 191 192.168.1.64/26 (subnet mask 255.255.255.192) Range is 64 192.168.1.128/26 (subnet mask 255.255.255.192) Range is 64

  20. 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

  21. ROUTE SUMMARIZATION IP address Binary Representation Bits in common 192.1.16.0 192.1.17.0 192.1.18.0 192.1.19.0 192.1.20.0 192.1.21.0 192.1.22.0 11000000.00000001.00010000.00000000 11000000.00000001.00010001.00000000 11000000.00000001.00010010.00000000 11000000.00000001.00010011.00000000 11000000.00000001.00010100.00000000 11000000.00000001.00010101.00000000 11000000.00000001.00010011.00000000 Will advertise as 192.1.16.0/21

  22. Route summarization What range of networks are summarized by the address and mask 192.1.32.0/19? 11000000.00000001.00100000.00000000 11000000.00000001.00100000.00000000 beginning range 192.1.32.0 11000000.00000001.00111111.00000000 ending range 192.1.63.0

  23. Network Planning Using Classless Routing & CIDR • Discontiguous (not next to one another) subnets cause unreliable routing • Avoid separating subnets with a different network • If you have discontiguous networks, turn AUTOMATIC SUMMARIZATION OFF and MANUALLY SUMMARIZE

  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 (discontiguous) • Update router IOS • Allow for future growth

  25. Configure/Verify Static and Dynamic NAT • RFC 1918: private IP address space • Class A: 10.0.0.0 - 10.255.255.255 • Class B: 172.16.0.0 - 172.31.255.255 • Class C: 192.168.0.0 - 192.168.255.255 • Routed internally, never on the Internet • “Hides” internal addresses from other networks

  26. Configure and Verify Static and Dynamic NAT • Network Address Translation (NAT) • NAT translates internal private addresses into one or more public addresses • Used on boundary routers to improve security and hide the host’s address

  27. Configure and Verify Static and Dynamic NAT • Inside local IP address—the PRIVATE IP address of an inside host as it appears to the inside private (local) network • Inside Global IP address—the PUBLIC IP address of an inside host as it appears to the outside network

  28. Configure and Verify Static and Dynamic NAT • Static NAT:map single inside local address to single public address • Dynamic NAT:use pool of public addresses to assign as needed R1(config)#ip nat pool TAME 209.165.201.23 209.165.201.30 netmask 255.255.255.224 R1(config)#ip nat inside source list 9 pool TAME THIS WILL CREATE A POOL OF 8 PUBLIC ADDRESS TO BE USED BY ALL THE COMPUTERS IN THE NETWORK (23, 24, 25, 26, 27, 28, 29, 30)

  29. Configure and Verify Static and Dynamic NAT • Port Address Translation (PAT) uses TCP or UDP port numbers • Another name for this is OVERLOAD • Dynamically translate multiple inside local addresses to share one public address

  30. 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

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