CCNA 3 v3. 1 Module 1

1. CCNA 3 v3.1 Module 1

2. CCNA 3 Module 1 Introduction to Classless Routing

3. Classfull Routing • IP V4 – class A, B,C • Limited number of unique network addresses • No subnet information sent in routing • A single network must use the same subnet mask • Network 192.168.187.0 - 255.255.255.0 • Classful routing protocols • Cannot support Variable Length Subnet Mask (VLSM) • RIP V1, IGRP, EGP, BGP3 • WAN and LAN links have the same • Number of bits in subnet mask • Number of possible hosts

4. IPv4 Address Classes • No medium size host networks • In the early days of the Internet, IP addresses were allocated to organizations based on request rather than actual need.

5. IPv4 Address Classes Class D Addresses • A Class D address begins with binary 1110 in the first octet • First octet range 224 to 239 • Class D address can be used to represent a group of hosts called a host group, or multicast group Class E Addresses • First octet of an IP address begins with 1111 • Class E addresses are reserved for experimental purposes and should not be used for addressing hosts or multicast groups

6. IP Addressing CRISIS • Address Depletion – shortage of ip addresses • Internet Routing Table Explosion – increase in the size of internet routing tables

7. A Waste of Space

8. Class C Address • LAN link has 28-2 = 254 possible hosts • WAN link has 28-2 = 254 possible hosts • WAN link only needs 2 hosts • 252 wasted host addresses IPv6 • 128 bit address space • Possible addresses • 2128-2 • 340,283,366,920,938,463,374,670,431,768,211,456

9. Variable Length Subnet Mask? • Short term extensions to IPv4 • Subnetting 1985 • Variable length subnetting 1987 • Classless Interdomain Routing 1993 • Allows for route aggregation and suppernetting • Private IP addresses • Network Address Translation (NAT)

10. Routing protocols that all Classless routing • Can have a variable length subnet mask • Protocols • OSPF • EIGRP • IS-IS • RIP V2 • Static Routing • BGP4

11. Route Aggregation with VLSMSummarisation • Represents a collection of IP Addresses within a Single IP Address • Place networks close to one another to save routing table space • keeping networks like 172.16.14.0 and 172.16.15.0 near one another so that the routers need only carry a route for 172.16.14.0/23 • Without this the internet backbone would collapse • Route summarization (or supernetting) • only possible if the routers run a classless routing protocol • E.g.s OSPF and IS-IS

12. Aggregation Rules • A router must know in detail the subnet numbers attached to it • A router does not need to tell other routers about each individual subnet if the router can send one aggregate route for a set of routers • A router using aggregate routes would have fewer entries in its routing table

13. VLSM allows for • the summarization of routes and increases flexibly • Bases summarization entirely on the higher-order bits shared on the left

14. variable-sized networks / subnetworks is summarized at various points using a prefix address until the entire network is advertised as a single aggregate route

15. What is a VLSM? • Variable Length Subnet Mask • Use address space more efficiently • Use a long mask on networks with few hosts • Use a short mask on subnets with many hosts

16. VLSM allows a single autonomous system to have networks with different subnet masks • a 30-bit subnet mask on network connections • 255.255.255.252 for networks with 2 nodes • Used for point-to-point connections • a 24-bit mask for user networks • 255.255.255.0 for networks up to 252 users • Wasteful for point-to-point networks • even a 22-bit mask for user networks • 255.255.252.0 for networks with up to 1000 users • Do a class example

17. When to use VLSM • When designing an addressing scheme • should allows for growth • not involve wasting addresses • VLSM helps to manage IP Addresses • Set subnet mask to suit the link or the segment requirements • To prevent waste of addresses use VLSM • Large subnets • Created for addressing LANs • Very small subnets • A 30-bit mask for subnets with only 2 valid host addresses • For a point-to-point connection • For WAN links • Example on board

18. First and Last Subnet Mask • Previously it was recommended not to use • First subnet – zero subnet – network address • Last subnet - all-ones subnet – broadcast address • VLSM allows • first and last subnets to be used If management decides to use subnet zero, it has 8 useable subnets ip subnet-zero If management decide not to use subnet 0 – 7 useable subnets no ip subnet-zero

19. RIP V1 • Distance vector protocol • Broadcasts entire routing table to each neighbor router • Broadcasts at intervals of 30 seconds • Metric is hop count • Classful routing – Class A, B, C • Prevents routing loops using • Maximum hop count – maximum 15 hops – after that packet is dropped • Split horizon – don’t teach the teacher • Holddown timers – ignore poorer metric information for 180 seconds • Popularity is based on • Simplicity and Load balancing over 6 equal-cost paths (4 paths default) • Limitations: • It does not send subnet mask information in its updates • It sends updates as broadcasts on 255.255.255.255. • It does not support authentication • It is not able to support VLSM or classless interdomain routing (CIDR) • Configuration • Router(config)#router rip • Router(config-router)#network <network number>

20. RIP V2 • Distance vector protocol • Metric is hop count • Prevents routing loops using • Uses a hop count metric- max 15 - 16 hops for infinite distance • Uses holddown timers to prevent routing loops – default 180sec • It uses split horizon to prevent routing loops • Provides prefix routing • Send out subnet mask information with route update • Supports classless routing (VLSM) • Different subnetworks can use different subnet masks • Provides for authentication in its updates • Clear text authentication key is the default • Message-Digest 5 (MD5) encryption • Used to authenticate the source of a routing update • It multicasts routing updates • Send routing updates to 224.0.0.9 instead of 255.255.255.255 • Uses External routing tags to separate RIP routes from externally learned routes

21. Configuring RIP Version 2 • Router(config)#router rip • Router(config-router)#version 2 • Router(config-router)#network <network no>

22. Verify RIP V2 with show ip protocols

23. Verifying Rip V2 using show ip route

24. Other verifications for RIP V2 • Show ip interface brief • Show running-config • Show ip protocols

25. Troubleshooting RIP V2 • debug ip rip • Displays rip routing updates as they are sent/recieved • No debug all • Turns off debugging

26. Default Routes • By default, routers learn paths to destinations three different ways: • Static routes – System administrator manually defines the static routes as the next hop to a destination - useful for security and traffic reduction, as no other route is known. • ip route <destination network> <subnet mask> <next hop> • Default routes – System administrator manually defines default routes as the path to take when there is no known route to the destination - keep routing tables shorter • ip route 0.0.0.0 0.0.0.0 <next hop> • Dynamic routes – Router learns of paths to destinations by receiving periodic updates from other routers • ip default-network <default network number> • All the packets that are not defined in the routing table will go to the nominated interface of the default router