1 CCNA 3 v3.1 Module 1

2 CCNA 3 Module 1 Introduction to Classless Routing

333 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 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

444 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.

555 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

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

777 A Waste of Space

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

999 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 VLSM Summarisation 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 and near one another so that the routers need only carry a route for /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 for networks with 2 nodes Used for point-to-point connections a 24-bit mask for user networks for networks up to 252 users Wasteful for point-to-point networks even a 22-bit mask for user networks 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 decide not to use subnet 0 – 7 useable subnets no ip subnet-zero If management decides to use subnet zero, it has 8 useable subnets 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 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

20 RIP V2 Distance vector protocol Metric is hop count Prevents routing loops using Uses a hop count metric- max 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 instead of 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

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 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 Dynamic routes – Router learns of paths to destinations by receiving periodic updates from other routers ip default-network All the packets that are not defined in the routing table will go to the nominated interface of the default router