Routing Protocols and Concepts – Chapter 7 ppsx

ƒ Difference between RIPv1 & RIPv2 ƒRIPv1 ƒRIPv1 •A classful distance vector routing protocol •Does not support discontiguous subnets •Does not support VLSM •Does not send subnet mask in

Routing Protocols and Concepts – Chapter 7

ƒ Encounter and describe the limitations of RIPv1’s cou e a d desc be e a o s o s

limitations.

ƒ Apply the basic Routing Information Protocol Version Apply the basic Routing Information Protocol Version

2 (RIPv2) configuration commands and evaluate RIPv2 classless routing updates.

ƒ Difference between RIPv1 & RIPv2

ƒRIPv1

ƒRIPv1

•A classful distance vector routing protocol

•Does not support discontiguous subnets

•Does not support VLSM

•Does not send subnet mask in routing update

•Routing updates are broadcast

ƒRIPv2

• A classless distance vector routing protocol that is an enhancement of RIPv1’s features

enhancement of RIPv1 s features.

• Next hop address is included in updates

• Routing updates are multicast ( 224.0.0.9 vs 255.255.255.255 )

http://www.cisco.com/univercd/cc/t d/doc/cisintwk/ito_doc/rip.htm

• The use of authentication is an option

Introduction

– Use of timers to prevent routing loops– Use of split horizon or split horizon with poison reverse to also help prevent routing loops

– Use of triggered updates when there is a change in the topology for faster convergence

Maximum hop count of 15 with the hop count of 16 signifying– Maximum hop count of 15, with the hop count of 16 signifying

an unreachable network

ƒ There exists a static summary route

ƒ Static route information can be

injected into routing table updates

using redistribution.

ƒ Routers 1 & 3 contain VLSM Routers 1 & 3 contain VLSM

networks

ƒ Remember that both the R1 and R3

routers have subnets that are part of

the 172 30 0 0/16 major classful

the 172.30.0.0/16 major classful

network (class B)

ƒ Also remember that R1 and R3 are

connected to R2 using subnets of the g

209.165.200.0/24 major classful

network (class C)

ƒ This topology is discontiguous and

will not converge because

will not converge because

172.30.0.0/16 is divided by the

209.165.200.0/24.

The configuration of this

summary route will be y

displayed later in this

section

RIP 1 Li it ti

RIPv1 Limitations

ƒ Review the VLSM addressing

scheme in the figure As shown

scheme in the figure As shown

in the top chart, both R1 and R3

have had the 172.30.0.0/16

network subnetted into /24

subnet and subnetted it again,

using the first four bits for g

subnets and the last four bits for

hosts The result is a

255.255.255.240 mask or /28

Subnet 1 and Subnet 2 are

Subnet 1 and Subnet 2 are

assigned to R3

ƒ Public IP addresses are used

on WAN links (through an

ISP, or when inside users

need to access outside sites,

a public IP address must be

used.)

ƒ Loopback interfaces

-These are virtual interfaces

that can be pinged and

that can be pinged and

added to routing table

Cisco has set these addresses aside for educational purposes

RIPv1 Limitations

ƒ Notice that R3 is using loopback interfaces (Lo0,

Lo1, and Lo2)

ƒ A loopback interface is a software-only interface that

is used to emulate a physical interface

is used to emulate a physical interface

ƒ Like other interfaces, it can be assigned an IP address

ƒ Loopback interfaces are also used by other routing

protocols, such as OSPF, for different purposes

ƒ These uses will be discussed in Chapter 11 OSPF.

ƒ In a lab environment, loopback interfaces are useful

in creating additional networks without having to add

more physical interfaces on the router

more physical interfaces on the router

ƒ A loopback interface can be pinged and the subnet

can be advertised in routing updates

ƒ Therefore, loopback interfaces are ideal for Therefore, loopback interfaces are ideal for

simulating multiple networks attached to the same

router

ƒ In our example, R3 does not need four LAN

interfaces to demonstrate multiple subnets and

interfaces to demonstrate multiple subnets and

VLSM Instead, we use loopback interfaces.

RIPv1 Limitations

ƒ Route redistribution

Redistribution involves taking the routes from one routing

– Redistribution involves taking the routes from one routing

source and sending those routes to another routing source.

• In our example topology, we want the RIP process on R2 to redistribute our static route (192.168.0.0/16) by importing the route into RIP and then sending it to R1 and R3 using the RIP process

R2( fi t )# di t ib t t ti -R2(config-router)#redistribute static

RIPv1 Limitations

ƒ R2(config)#ip route 192.168.0.0 255.255.0.0 Null0

The address space represented by the static summary route

–The address space represented by the static summary route 192.168.0.0/16 does not actually exist

–In order to simulate this static route, we use a null interface as the exit interface

– You do not need to enter any commands to create or configure the null interface

configure the null interface

–It is always up but does not forward or receive traffic Traffic sent to the null interface is discarded

Static routes and null interfaces

ƒ Static routes and null interfaces Stat c outes a d u te aces

R2(config)#ip route 192.168.0.0 255.255.0.0 Null0

ƒ a static route must have an active exit interface a static route must have an active exit interface before it will be installed in the routing table

ƒ Using the null interface will allow R2 to advertise the g static route in RIP even though networks belonging

to the summary 192.168.0.0/16 do not actually exist.

V if i d T ti C ti it

Verifying and Testing Connectivity

ƒ show ip interfaces brief

T t t h th t th t l h f ll

– To test whether or not the topology has full

connectivity, we first verify that both serial

links on R2 are up using the show ip

interface brief

ƒ Ping

ƒ Whenever R2 pings any of the 172.30.0.0 subnets

on R1 or R3, only about 50% of the ICMP are

successful.

ƒ R1 is able to ping 10.1.0.1 but is unsuccessful

when attempting to ping the 172.30.100.1 on R3

ƒ R3 is able to ping 10 1 0 1 but is unsuccessful

ƒ R3 is able to ping 10.1.0.1 but is unsuccessful

when attempting to ping the 172.30.1.1 on R1

RIP 1 Li it ti

RIPv1 Limitations

ƒ RIPv1 – a classful routing protocol

– Subnet mask Subnet mask are not sent are not sent in updates in updates

– Summarizes networks at major network boundaries

–RIPv1 cannot support discontiguous networks, VLSM, or CIDR

RIP 1 Li it ti

RIPv1 Limitations

ƒ Examining the routing tables

-To examine the contents of

routing updates use the

debug ip rip command

R2 i i i t 172 30 0 0 l t

R2 is receiving two 172.30.0.0 equal cost

routes with a metric of 1 hop R2 is

receiving one route on Serial 0/0/0 from R1

and the other route on Serial 0/0/1 from R3.

R2 has two equal cost routes to the 172.30.0.0/16 network

RIP 1 Li it ti

RIPv1 Limitations

•R1 has its own 172 30 0 0 routes:

•R1 has its own 172.30.0.0 routes:

172.30.2.0/24 and 172.30.1.0/24

•But R1 does not send R2 those subnets

•R3 has a similar routing table

B th R1 d R3 b d t d

•Both R1 and R3 are boundary routers and

are only sending the summarized

172.30.0.0 network to R2 in their RIPv1

routing updates

A lt R2 l k b t th

•R2 that it is not including the 172.30.0.0 network

in its updates to either R1 or R3

•Because the split horizon rule is in effect

•R2 learned about 172 30 0 0/16 on both the

•As a result, R2 only knows about the

172.30.0.0/16 classful network and is

unaware of any 172.30.0.0 subnets.

•R2 learned about 172.30.0.0/16 on both the Serial 0/0/0 and Serial 0/0/1 interfaces, it does not include that network in updates it sends out these same interfaces.

RIPv1 Limitations

ƒ Because RIPv1 does not send the

subnet mask in routing updates, it g p R4 is added to

cannot support VLSM

ƒ R3 router is configured with VLSM

subnets all of which are members

R4 is added to the topology connected to R3

subnets, all of which are members

of the class B network

– RIPv1 either summarizes the

subnets to the classful boundary

– or o uses the subnet mask of the uses t e sub et as o t e

outgoing interface to determine

which subnets to advertise.

RIPv1 Limitations

ƒ Why is RIPv1 on R3 not including

the other subnets,

Those subnets do not have the same subnet mask as

FastEthernet 0/0

– R3 will only include those

172 30 0 0 routes in its routing

172.30.0.0 routes in its routing table with the same mask as the exit interface

– Since the interface is 172.30.100.1

do not match the /24 mask of the outgoing interface

– the static route is included in

R2's routing table, but R2 will

not include the static route in its

not include the static route in its

update

– R1 is not receiving this

192.168.0.0/16 route in its RIP

updates from R2,

ƒ Reason: Classful routing

protocols do not support

CIDR routes that are

summarized with a smaller

mask than the classful

subnet mask

– If the 192.168.0.0 static route

were configured with a /24 mask

or greater, this route would be g ,

included in the RIP updates

Config ring RIP 2

ƒ Comparing RIPv1 & RIPv2 Message Formats

– RIPv2 Message format is g similar to RIPv1 but has 2 extensions

1st extension is the subnet mask field

ƒ allows a 32 bit mask to be included in the RIP route entry.

ƒ the receiving router no longer depends upon the subnet mask of the the receiving router no longer depends upon the subnet mask of the inbound interface or the classful mask when determining the subnet mask for a route

2nd extension is the addition of next hop address

ƒ The Next Hop address is used to identify a better next-hop address - if one exists - than the address of the sending router

ƒ If the field is set to all zeros (0.0.0.0), the address of the sending router

is the best next-hop address

is the best next-hop address

Configuring RIPv2

–By default it is running RIPv1–Even though the router only sends RIPv1 messages, it can interpret both RIPv1 and RIPv2 messages

interpret both RIPv1 and RIPv2 messages

–A RIPv1 router will just ignore the RIPv2 fields in the route entry

Configuring RIPv2

ƒ Configuring RIPv2 on a Configuring RIPv2 on a

Cisco router

-Requires using the

-Requires using the

version 2 command

RIPv2 ignores RIPv1

-RIPv2 ignores RIPv1

Comparing RIP v1 and v2

ƒ RIP v2 Æ send and receive v2

ƒ RIP v1 RIP v1 Æ send v1 but can receive both v1 and v2 Æ send v1 but can receive both v1 and v2

Yes I can take

version 2

C fi i RIP 2

Configuring RIPv2

summarize routes at major

summarize routes at major

can also summarize routes

with a subnet mask that is

smaller than the classful

subnet mask

Configuring RIPv2

Each subnet and mask has its own specific entry, along with the exit interface and next-hop address to reach that subnet.

ƒ To verify information being sent by RIPv2 use the y g y

debug ip rip command

RIPv2) to disseminate network addresses and their subnet

and their subnet masks

VLSM & CIDR

being sent and

being sent and

received use the

following commands

-Show ip route Debug ip rip -Debug ip rip

Verifying & Troubleshooting RIPv2

ƒ Basic Troubleshooting steps

-Check the status of all links -Check cabling Check cabling

-Check IP address & subnet mask configuration -Remove any unneeded configuration commands

– Show ip protocols p p

Verifying & Troubleshooting RIPv2

C RIP 2 I

ƒ Common RIPv2 Issues

ƒ When trouble shooting RIPv2 examine the following issues:

V if i & T bl h ti RIP 2

Verifying & Troubleshooting RIPv2

ƒ Reasons why it’s good to authenticate routing information y g g

-Prevent the possibility of accepting invalid routing updates-Contents of routing updates are encryptedg p yp

ƒ Types of routing protocols that can use authentication

-RIPv2RIPv2-EIGRP-OSPFOSPF-IS-IS-BGP

Routing

Protocol

Distance Vector

Classless Routing Protocol

Uses Hold- Down

Use of Split Horizon

Max Hop count

Auto Summary

Support CIDR

Supports VLSM

Uses Authen- tication Timers or

Split Horizon w/

Poison

= 15

Poison Reverse