Ccna2 M6 Routing And Routing Protocols

CCNA – Semester2

Module 6 Routing and Routing Protocols

Objectives

• Introduction to static routing • Dynamic routing overview • Routing protocols overview

Introduction to Static Routing

Introducing routing • Routing is the process that a router uses to forward packets toward the destination network. • A router makes decisions based upon the destination IP address of a packet. • In order to make the correct decisions, routers must learn the direction to remote networks.

Route Types

The Administrative Distance • AD is a rating of the trustworthiness of a routing information source, expressed as a numeric value from 0 to 255. The higher the number, the lower the trustworthiness rating. • Example: – – – – –

Directed connection Static route (by default) IGRP OSPF RIP

0 1 100 110 120

Static route • Advantages: – Require very little maintenance on small networks – No network overhead – May hide parts of networks

• Disadvantages: – Require a tremendous amount of administrative time on large networks – Lack scalability

The IP ROUTE command Router (config)# ip ip route route network network [[ mask mask ]] {{ address address || interface interface }} [[ distance distance ]] [[ permanent ] permanent ]

• Defines a path to an IP destination network or subnet ip route command

Description

network

destination network

mask

dest. network mask

address

IP address of next hop

interface

Name of interface to get to destination

distance

Administrative distance

permanent

if set, route will not be removed when intf. is shutdown

Static route command

AD in static route • A route with a lower AD will be installed before an identical route with a higher AD. • The default AD when using next-hop address is 1, while the default AD when using the outgoing interface is 0. • If an administrative distance other than the default is desired, a value between 0 and 255 is entered

Route in Routing Table • If the router cannot reach the outgoing interface that is being used in the route, the route will not be installed in the routing table. • This means if that interface is down, the route will not be placed in the routing table • To hold the route in routing table even if associated outgoing interface is down, use permenent parameter.

Default Route • Default routes are used to route packets with destinations that do not match any of the other routes in the routing table. • Routers are typically configured with a default route for Internet-bound traffic. ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface]

Using the DEFAULT IP ROUTE command

Verifying static route configuration • show running-config to verify that the static route was entered correctly. • show ip route command to make sure that the static route is present in the routing table.

Troubleshooting static route configuration

• Show ip route command • Ping command • Traceroute command

Dynamic Routing Overview

Routed Protocol • A routed protocol is used to direct user traffic. • A routed protocol provides enough information in its network layer address to allow a packet to be forwarded from one host to another based on the addressing scheme. • Examples of routed protocols are: – Internet Protocol (IP) – Internetwork Packet Exchange (IPX)

Routing Protocol • A routing protocol is the communication used between routers. • A routing protocol allows one router to share information with other routers regarding the networks it knows about. • Examples of routing protocols are: – – – –

Routing Information Protocol (RIP) Interior Gateway Routing Protocol (IGRP) Enhanced Interior Gateway Routing Protocol (EIGRP) Open Shortest Path First (OSPF)

Autonomous systems • •

•

An autonomous system (AS) is a collection of networks under a common administration sharing a common routing strategy. The American Registry of Internet Numbers (ARIN), a service provider, or an administrator assigns an identifying number to each AS. This autonomous system number is a 16 bit number.

Purpose of a routing protocol • The goal of a routing protocol is to build and maintain the routing table. • This table contains the learned networks and associated ports for those networks.

Updating route • The routing protocol learns all available routes, places the best routes into the routing table, and removes routes when they are no longer valid. • The network knowledgebase needs to reflect an accurate consistent view of the current topology.

Convergence • When all routers in an internetwork are operating with the same routing knowledge, the internetwork is said to have converged. • During convergence, problems may occur like: routing loops, inconsistent traffic forwarding, inconsistent routing table entries. • Fast convergence is desirable because it reduces the period of time in which routers would continue to make incorrect routing decisions.

Classes of routing protocols • Most routing algorithms can be classified into one of two categories: – distance vector – link-state

Distance vector algorithm • Pass periodic routing update (copies of a routing table) from router to router. • These regular updates between routers communicate topology changes. • Each router receives a routing table from its directly connected neighbors. • Distance-vector algorithms do not allow a router to know the exact topology of an internetwork.

Distance Vector Discovery

Link-State Routing • Also known as Dijkstras algorithm or as SPF (shortest path first) algorithms. • Link-state routing algorithms maintain a complex database of topology information • A link-state routing algorithm maintains full knowledge of distant routers and how they interconnect.

Link-State Concepts

Link-State Concerns

Distance Vector vs. Link State

Routing Protocols Overview

Router Functions • A router has two basic functions: – Path determination occurs at the network layer, enables a router to evaluate the paths to a destination – Switching function is the internal process used by a router to accept a packet on one interface and forward it to a second interface on the same router.

Communicate Path Information

Addressing: Network and Host

• •

Network address: Used to determine path to a network Host address: Specifies specific port or device on a network

How distances are determined • Primary objective of routing protocol is to determine the best route to put in the routing table. • Each routing algorithm interprets what is best in its own way. • Routing algorithm generates a number, called the metric value, for each path through the network. • Typically, the smaller the metric number, the better the path.

Distance in Metrics

The router and network Commands

IP Routing Configuration Tasks

Routing protocols

Routing Information Protocol (RIP) • It is a distance vector routing protocol. • Hop count is used as the metric for path selection. • If the hop count is greater than 15, the packet is discarded. • Routing updates are broadcast every 30 seconds, by default.

Interior Gateway Routing Protocol (IGRP) • Cisco proprietary protocol • It is a distance vector routing protocol. • Bandwidth, load, delay and reliability are used to create a composite metric. • Routing updates are broadcast every 90 seconds, by default.

Open Shortest Path First (OSPF) • It is a link-state routing protocol. • Open standard routing protocol described in RFC 2328. • Uses the SPF algorithm to calculate the lowest cost to a destination. • Routing updates are flooded as topology changes occur.

Enhanced-IGRP (EIGRP) • • • •

Cisco proprietary protocol It is an enhanced distance vector routing protocol. Uses load balancing. Uses a combination of distance vector and link-state features. • Uses Diffused Update Algorithm (DUAL) to calculate the shortest path. • Routing updates are broadcast every 90 seconds or as triggered by topology changes.

Border Gateway Protocol (BGP) • • • •

Exterior routing protocol. It is a distance vector exterior routing protocol. Used between ISPs or ISPs and clients. Used to route Internet traffic between autonomous systems.

Summary • Configure static route, default route, float static route • Protocol administrative distance • Routed and routing protocol • Distance vector and link state routing protocol • Router functions • Routing protocols metrics • IP routing configuration tasks

Lab Topology F0/0

F0/0

S0/0 S0/1

Lab_E

Lab_B

S0/1

S0/0

S0/1

S0/1

S0/1

Lab_C

Lab_A

S0/0 S0/0

F0/0

F0/0

S0/1

Lab_F

Lab_D F0/0

F0/0

Port

Lab_A

Lab_B

Lab_C

Lab_D

Lab_E

Lab_F

S0/0

N/A

199.6.13.1/24

204.204.7.1/24

142.18.0.1/16

34.10.120.1/16

N/A

S0/1

201.10.11.1/24

201.10.11.2/24

199.6.13.2/24

204.204.7.2/24

142.18.0.2/16

34.10.210.5/16

F0/0

172.16.11.1/24

10.0.0.1/8

172.16.11.2/24

192.168.1.1/24

10.0.0.2/8

192.168.1.2/24

CCNA2 – Module6