_ccn(lab#6&7)

LAB # 6&7

ROUTING INFORMATION

PROTOCOL (RIPv1 & RIPv2)

Routing Protocols

• Routing protocols

– Protocols used by routers to make path determination

choices and to share those choices with other routers

• Hop count

– The number of routers a packet must pass through to

reach a particular network

• Metric

– A value used to define the suitability of a particular

route

– Routers use metrics to determine which routes are

better than other routes

Routing Protocols (continued)

• Autonomous system (AS)

– Uses Interior Gateway Protocols as routing protocols

– A group of routers under the control of a single

administration, sharing a common routing strategy.

• Interior Gateway Protocols (IGPs) are

– Routing protocols used within an AS

• Exterior Gateway Protocols (EGPs)

– Routing protocols used to route information between

multiple autonomous systems

Autonomous System

AS 2000

AS 3000

IGP

Interior Gateway Protocols are

used for routing decisions

within an Autonomous System.

Exterior Gateway

Protocols are used

for routing between

Autonomous Systems

EGP

AS 1000

An Autonomous System (AS) is a group of IP networks, which has a single and clearly defined routing policy. Group of routers which can exchange updates AS are identified by numbers

Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67)

All Routing protocols are categorized as IGP or EGP

Routing Categories

IGP

Interior Gateway Protocol

(IGP)

Exterior Gateway

Protocol (EGP)

EGP

EGP

EGP

Interior Gateway Protocol

(IGP)

AS 1000

AS 2000

AS 3000

Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67)

Routing Categories

Autonomous Systems: Interior or Exterior

Routing Protocols

An autonomous system is a collection of networks under a common administrative domain.

IGPs operate within an autonomous system.

EGPs connect different autonomous systems.

Distance Vector

RIP V1

IGRP

RIP V2

Link state

OSPF

Hybrid

EIGRP

Types or Classes of Routing Protocols

Class-full Routing Overview

Class-full routing protocols do not include the subnet mask with the route advertisement.

Within the same network, consistency of the subnet masks is assumed.

Summary routes are exchanged between foreign networks.

Examples of class-full routing protocols:

RIP Version 1 (RIPv1)

IGRP

Classless Routing Overview

Classless routing protocols include the subnet mask with the route advertisement.

Classless routing protocols support variable-length subnet masking (VLSM) and sub-netting.

Examples of classless routing protocols:

RIP Version 2 (RIPv2)

EIGRP

OSPF

Distance Vector

There are two Distance Vector Protocol, Both uses different metric

RIP – Hops

IGRP - Internetwork delay, bandwidth, reliability, and load are all factored into the routing decision.

192.168.10.1

192.168.20.1

192.168.10.1 192.168.20.1

Distance Vector

Distance Vector protocols are known as Routing by rumor. RIP uses only Hop count RIP routing table metric for 192.168.20.1 network will be

3 2

192.168.10.1

192.168.20.1

0

1

1

2

2

3 R1R1

192.168.10.1

192.168.20.1

Distance Vector

192.168.10.1

192.168.20.1

56 kbps

1 Mbps 1 Mbps

1 Mbps

56 kbps

• IGRP uses bandwidth and delay as Metric • Routing table metric for 192.168.20.1 network will be

– 30 – 60

R1 10

10

10

30 30 192.168.10.1

192.168.20.1

DISTANCE VECTOR ROUTING

PROTOCOLS

– Broadcast their entire routing table to each neighbor

router at predetermined intervals

– The actual interval depends on the distance-vector

routing protocol in use

• Varies between 30 and 90 seconds

– Sometimes referred to as routing by rumor

– Suffer from slow time to convergence

• A state where all routers on the internetwork share a

common view of the internetwork routes

Routing Information Protocol

• Routing Information Protocol (RIP)

– The easiest Interior Gateway Protocol to configure is

RIPv1

– A distance-vector routing protocol that broadcasts

entire routing tables to neighbors every 30 seconds

– RIP uses hop count as its sole metric

• RIP has a maximum hop count of 15

– As a result, RIP does not work in large internetworks

• RIP is capable of load balancing

• RIP is susceptible to all the problems normally

associated with distance-vector routing protocols

• Routers discover the best path to destinations from each neighbor.

Sources of Information and Discovering

Routes

• Each node maintains the distance from itself to each possible destination network.

Inconsistent Routing Entries

• Slow convergence produces inconsistent routing.

Inconsistent Routing Entries (Cont.)

• Router C concludes that the best path to network 10.4.0.0 is

through router B.


• Router A updates its table to reflect the new but

erroneous hop count.


Hop count for network 10.4.0.0 counts to infinity.

Count to Infinity

• Packets for network 10.4.0.0 bounce (loop) between routers B and C.

Routing Loops

• Define a limit on the number of hops to prevent infinite loops.

Defining a Maximum

Maximum Hop Count

• One way of solving routing loop problem is to define a maximum hop count.

• RIP permits a hop count of up to 15, so anything that requires 16 hops is deemed unreachable

• The maximum hop count will control how long it takes for a routing table entry to become invalid

Split Horizon

Split-horizon Route Advertisement is a method

of preventing routing loops in distance-vector

routing protocols by prohibiting a router from

advertising a route back onto the interface from

which it was learned.

Split Horizon is a rule that routing information cannot be sent back in the direction from which it was received.

Route Poisoning • Route Poisoning is usually used in conjunction with split

horizon.

• For example if Router A goes down, Router B initiates route poisoning by advertising the network between A and B as unreachable.

• When router C receives a route poisoning from B, it sends an update, called a poison Reverse back to B.

• This ensures that all routes on the segment have received the poisoned route information.

Hold-downs

• Hold-downs are a technique used to ensure that a route recently removed or changed is not reinstated by a routing table update from another route.

• Hold-down prevents regular update messages from reinstating a route that is going up and down (called flapping).

• Hold-downs make a router wait a period of time before accepting an update for a network whose status or metric has recently changed.

RIP TIMERS • Route Update Timer - The routing-update timer

clocks the interval between periodic routing updates. It

is usually set to 30 seconds.

• Route Invalid Timer - The Route Invalid Timer

determines the length of time (90 seconds) before a

route is considered invalid. If it doesn't receive an

update for the route it sets the route as invalid and

notifies its neighbors.

• Route Flush Timer - The Route Flush Timer sets the

time between when a route becomes invalid and its

removal from the routing table (240 seconds). Time

must be longer than invalid timer so it can tell its

neighbors about the route.

Enabling RIP Routing

Enabling RIP Routing (continued)

• To start configuring RIP, you must:

– Enter privileged mode first

– Enter global configuration mode on your router

• Enable RIP with the router rip command

Enabling RIP Routing (continued)

Configuring RIP Routing for Each

Major Network

• network command

– Turns on RIP routing for a network

– An individual network command must be issued for

each separate network directly connected to the router

• show ip route command

– Displays a router’s routing table

• Administrative distance

– A value used to determine the reliability of the

information regarding a particular route

– Administrative distances range from 0–255

Configuring RIP Routing for Each

Major Network (continued)

Show ip protocol and debug ip

rip Commands

• Commands used to monitor RIP

• A route is considered invalid if six consecutive

update intervals pass without an update from that

route

• Flush interval

– The time at which a route will be totally removed from

the routing table if no updates are received

• debug ip rip command

– Displays real-time rip updates being sent and received

and places very high processing demands on your

router, which could affect network performance

Show ip protocol and debug ip

rip Commands (continued)

Summary

Routing Information Protocol (RIP) is a true distance-vector routing protocol.

It sends the complete routing table out to all active interfaces every 30 seconds

RIP only uses hop count to determine the best way to a remote network

It has a maximum allowable hop count of 15 AD is 120 Works well in small networks, but it’s inefficient on large

networks RIP version 1 uses only class-full routing. RIP version 2 does send subnet mask information with the

route updates. This is called classless routing.

_ccn(lab#6&7)

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