CCNA 2 Week 6 Routing Protocols. Copyright © 2005 University of Bolton Topics Static Routing Dynamic Routing Routing Protocols Overview

CCNA 2 Week 6

Routing Protocols

Copyright © 2005 University of BoltonCopyright © 2005 University of Bolton

Topics

Static Routing

Dynamic Routing

Routing Protocols Overview


Introduction to Routing

Routing is the process used by a router to forward packets towards the destination network

To make decisions routers learn about remote networks

Dynamic routing - information is learned from other routers

Static routing - network administrator configures network information manually


Adding Static Routes

In Global Config mode:– ip route net_addr netmask gateway– ip route 10.0.0.0 255.0.0.0 s1/0– ip route 10.3.0.0 255.255.0.0 10.2.0.1

Can add optional administrative distance param

Use show ip route to view routing table


Step-by-step

1. Determine all desired prefixes, masks, and addresses

2. Enter global configuration mode.

3. Type the ip route command with a prefix and mask followed by the corresponding address from Step 1. The administrative distance is optional.

4. Repeat Step 3 for all the destination networks in Step

5. Exit global configuration mode.

6. copy running-config startup-config


Default Route

Impossible to write for every combination when using static routes

Typically add a default entry to send packets that don't match any rules to a default gateway router

ip route 0.0.0.0 0.0.0.0 gateway


Testing

show ip route – displays routing table

show running-config– displays config file as entered

Use ping command to test connectivity

Use traceroute command to determine where mis-configuration occurs

Dynamic Routing


Routing Protocols

Used by routers to share information about connected networks

Examples of routing protocols are as follows:– Routing Information Protocol (RIP) – Interior Gateway Routing Protocol (IGRP) – Enhanced Interior Gateway Routing Protocol (EIGRP) – Open Shortest Path First (OSPF)


Autonomous Systems (AS)

"An AS is a collection of networks under a common administration that share a common routing strategy. "

Viewed by outside world as single entity

Each AS assigned unique 16-bit number by authority such as ARIN


Goal of routing protocols

Build routing table using data learned from neighbours

Best routes are placed in routing table

Table recalculated when changes occur

When all routers share optimum config – network is said to be converged


Protocol classes

Distance Vector– Determines direction and distance (vector) to other

networks

Link-state– Each router builds a copy of network topology– Reflects network conditions


Distance Vector overview

Routers receive copies of neighbours' routing tables

Links to connected networks given metric such as hop count

Add details to own tables with neighbour as gateway (updating routing metric)

Details spread through networks as learned routes are passed on

Routers choose best route to distant networks


Link-state overview

Each router builds a detailed topology database of remote routers and their networks

Builds a tree-structure with self as route

Uses SPF algorithm (Dijkstra's) to calculate best routes

Link State Advertisements update neighbours of changes and recalculate topology database


Comparison

Link-state algorithms generally require– greater CPU power than Distance Vector– more memory to maintain topology– greater initial bandwidth for convergence

Once stable, minimal overhead is required to maintain

Routing Protocols Overview


Path Determination

Path Determination Function– Uses layer 3 addressing – Routing table to determine outbound interface

Switching Function– Packets forwarded to appropriate interface– Layer 2 encapsulation appropriate for next data link


Routing Configuration

Global task to specify routing protocol to use

GAD(config)# router rip

Routing configuration mode used to...– specify networks

GAD(config-router)# network 192.168.77.0– Configure protocol settings such as update intervals

and timeouts


RIP

RIP a basic routing protocol for small networks. Its key characteristics include the following:

– 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.


IGRP

IGRP is a proprietary protocol developed by Cisco. Some of the IGRP key design characteristics are as follows:

– 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.

IGRP is being phased out by Cisco


OSPF

OSPF is a nonproprietary link-state routing protocol.

– It is a link-state routing protocol. – It is an open standard routing protocol described in

RFC 2328. – The SPF algorithm is used to calculate the lowest cost

to a destination. – Routing updates are flooded as topology changes

occur.


EIGRP

EIGRP is a Cisco proprietary enhanced distance vector routing protocol. Key characteristics:

– It uses unequal cost load balancing. – It uses a combination of distance vector and link-state

features. – It uses Diffused Update Algorithm (DUAL) to calculate

the shortest path. – Routing updates are multicast using 224.0.0.10

triggered by topology changes.


BGP

Border Gateway Protocol (BGP) is an exterior routing protocol. The key characteristics of BGP are as follows:

– It is a distance vector exterior routing protocol. – It is used between ISPs or ISPs and clients. – It is used to route Internet traffic between autonomous

systems.


IGP vs EGP

Interior Gateway protocol within AS

Exterior Gateway protocol between AS

EGPs require:– A list of neighbor routers with which to exchange

routing information – A list of networks to advertise as directly reachable – The autonomous system number of the local router

Documents

CCNA 2 Week 6 Routing Protocols. Copyright © 2005 University of Bolton Topics Static Routing Dynamic Routing Routing Protocols Overview