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Introduction to Classless Routing

Introduction to Classless Routing. VLSM RIP Version 2. Introduction to Classless Routing. Variable Length Subnet Masks. Classful Routing. IP Version 4 provides Classes A, B, C Limited Number of unique network addresses Complex Routing tables

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Introduction to Classless Routing

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  1. Introduction to Classless Routing VLSM RIP Version 2

  2. Introduction to Classless Routing Variable Length Subnet Masks

  3. Classful Routing • IP Version 4 provides Classes A, B, C • Limited Number of unique network addresses • Complex Routing tables • No subnet information sent in routing updates by classful routing protocols e.g. RIP v1, IGRP

  4. Head Office Problem 1a • FSF Ltd has been allocated a class C address • It has 3 branch offices with a requirement of 10 hosts per network connecting via point to point links to the Head Office with 25 hosts • Design a subnet mask for FSF

  5. Problem 1b • FSF Ltd plans • 3 additional branch offices (10 hosts per LAN) • Head Office (25 hosts) • Design a new subnet mask

  6. Problem 1b continued Variable Length Subnet Mask • Use 27 bit mask for head office (5 host bits = 32 hosts) • Use 28 bit mask for branch offices (4 host bits = 16 hosts) • Use 30 bit mask for router to router links (2 host bits = 4 hosts) • Using 192.168.200.0 write out the addressing scheme for this network

  7. Problem 2 • Most class A & B network addresses allocated • PHS Ltd with 800 hosts wants IP addresses for its network • 4 different Class C network addresses needed • 4 routing table entries for that network

  8. Solution 2 – Part 1 • ISP allocates 212.23.24.0 to 212.23.27.255 • Routing table entry for PHS is • 212.23.24.0 /22 OR • 212.23.24.0 255.255.252.0 • 22 bit mask in binary: • 11111111.11111111.11111100.00000000 • This mask groups 4 class C networks into 1 network & routing table entry

  9. Solution 2 – Part 2 • 11010100.00010111.00011000.00000000 (Network) • 11111111.11111111.11111100.00000000 (Mask)

  10. Problem 3 • PHS Ltd has 4 class C address blocks allocated • It does not want to waste the addresses it has been given • The network administrator has the following requirements based on current use & future growth needs Head Office - 500 hosts Factory - 50 hosts Logistics Centre – 80 hosts Customer support Centre – 220 hosts Question: What is the appropriate VLSM mask solution for PHS Ltd?

  11. Internet 212.23.24.0 /22 212.23.24.0 /23 Head Office 212.23.27.0 /30 212.23.27.8 /30 212.23.27.4 /30 Customer Services Logistics Factory 212.23.26.0 /24 212.23.27.64 /26 212.23.27.128 /25 Solution 3 (example) List the addresses • On interfaces • On each site • Still available

  12. Requirements for classless routing • Classless routing protocol e.g. EIGRP, OSPF, RIP v2 • Contiguous network addresses to allow route aggregation

  13. Introduction to Classless Routing RIP Version 2

  14. RIP Version 1 Review • Supported by most routers • Distance Vector routing protocol • Metric – hop count • 15 hop maximum count • Periodic routing updates (30 seconds) • Routing updates broadcast to 255.255.255.255 • Uses holddown timers • Does not send subnet information in updates • Does not support authentication

  15. RIP v2 enhancements • Sends subnet information in updates – supports CIDR & VLSM • Supports authentication • Updates multicast to 224.0.0.9

  16. IOS RIP v2 Command • Enable RIP v2 Router(config)#router rip Router(config-router)#version 2 Router(config-router)#network 10.0.0.0

  17. Verifying Routing Protocols • Check the configuration of routing protocols Router#show ip protocols Router#show running-config • Viewing RIP updates Router#debug ip rip

  18. Configuring Routes • Static Routes Router(config)#ip route 192.168.2.0 255.255.255.0 192.168.1.1 ip route destination network gateway Default Route Router#ip route 0.0.0.0 0.0.0.0 192.168.1.1 • Defines the default gateway for all routes • Keeps routing tables small

  19. Default Network • 1 router on a network must have a default route on the network e.g. Router#ip route 0.0.0.0 0.0.0.0 192.168.1.1 • Other routers can have a default network set Router#ip default network 192.168.1.0 Traffic for destinations outside of the LAN will be sent to the router with the network address 192.168.1.0

  20. Labs • 1.1.4 Calculating VLSM Subnets • 1.2.3 Review of Basic Router Configuration with RIP • 1.2.4 Converting RIP v1 to RIP v2 • 1.2.5 Verifying RIP v2 Configuration • 1.2.6 Troubleshooting RIP v2 using Debug

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