Chapter 06 - OSPF and EIGRP

7/27/2019 Chapter 06 - OSPF and EIGRP

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Chapter 6

Routing Protocol EIGRP

And OSPF



LINK-STATE ROUTING

PROTOCOL



Link-state routing protocol features

Uses the hello information and Link-state advertisements(LSAs) it receives from other routers to build a database about

the network A topological database

Uses the shortest path first (SPF) algorithm (Dijkstra algorithm)to calculate the shortest route to each network

The resulting SPF tree

Stores this route information in its routing table



How routing information is maintained

When a failure occurs in the network, each link-state router takeflowing action:

Flood LSAs using a special multicast address throughout an

area.Copy of the LSA and updates its link-state, or topologicaldatabase.

Then forward the LSA to all neighboring devices

Recalculate their routing tables.



OSPF



SINGLE AREA OSPFCONCEPTS



OSPF overview

Open Shortest Path First (OSPF) is a link-state routing protocolbased on open standards.

The most recent description is RFC 2328. The Open in OSPFmeans that it is open to the public and is non-proprietary.



OSPF terminology



OSPF terminology: Area

A collection of networks and routers that have the same area identification.

TokenRing

Area 1 Area 0



OSPF terminology: Adjacencydatabase

A listing of all the neighbors to which a router has established

bi-directional communication. Not every pair of neighboringrouters become adjacent

Adjacencydatabase

Neighbors

TokenRing



OSPF terminology: Link-statedatabase

Also known as a topological database A list of link-state entries of all other routers in the internetwork

TokenRing

TopologicalDatabase

Adjacencydatabase



OSPF terminology: Routing table

The routing table (also known as forwarding database)generated when an algorithm is run on the link-state database.

Each router’s routing table is unique

AdjacencyDatabase

Lists neighbors

TokenRing

TopologicalDatabase

Lists all routes Routing

TableLists best routes



Configuring OSPF loopback address

Router ID:

Number by which the router is known to OSPF

Router ID is Highest IP address of any active loopback interface. If there isno looback interface then Router ID is The highest IP address on an active

interface at the moment of OSPF process startup EX : Configuring ip address to loopback interface

Router(configf)#Interface loopback 0Router(configf-if)#ip address 192.168.31.33 255.255.255.0



OSPF terminology: DR and BDRrouter

Designated router (DR) and backup designated router (BDR): A router that is elected by all other routers on the same LAN

to represent all the routers.

Each network has a DR and BDR

TokenRing

DR

BDR



Electing the DR and BDR (ifnecessary).

P=1 P=0P=1

P=3 P=2

DR BDR

Hello

• The router with the highest priority value is the DR.• The router with the second highest priority value is the BDR.• The default for the interface OSPF priority is 1. In case of the

same priority, Router has the highest router ID is DR. Routerhas the second highest router ID is BDR



Shortest path algorithm

1

4

1 4

2

22

ABC

D

E F G

The best path is the lowest cost path.



Modifying OSPF cost metric

Cost is calculated using the formula 108 /bandwidth, where bandwidth is expressedin bps.

Bandwidth dividend is user configurable: Interface subcommand: bandw idth 64

Interface subcommand: ip o sp f co st <1-65535>

Relevant going out an interface only

Medium Cost

56 kbps serial link 1785

T1 (1.544 Mbps serial link) 64

E1 (2.048 Mbps serial link) 48

Ethernet 10

Fast Ethernet/FDDI 1



OSPF network types



OSPF network types: Fourth type



OSPF Hello Protocol

The rules that govern the exchange of OSPF hello packets are calledthe Hello protocol.

Hello packets use : 224.0.0.5 (all routers).

Hello packets are sent at regular intervals (default):

Multi access and Point-to-point: 10s

NBMA : 30s

On multi-access networks the Hello protocol elects a designatedrouter (DR) and a backup designated router (BDR).

The hello packet carries information that all neighbors must agreeupon before an adjacency is formed, and link-state information isexchanged.



Establish router adjacencies

Router IDHello/dead intervals

NeighborsArea-ID

Router priorityDR IP address

BDR IP addressAuthentication password

Stub area flag

* *

**

* Entry must match on neighboring routers

Hello

afadjfjorqpoeru39547439070713

Hello

A

D E

CB



Steps in the operation of OSPF

5 steps of operation:

1. Establish router adjacencies.

2. Elect a DR and BDR (if necessary).

3. Discover routes.

4. Select the appropriate routes to use.

5. Maintain routing information.



Step 1: Establish router adjacencies

First step in OSPF operation is to establish router adjacencies

RTB sends hello packets, advertising its own router ID highest IPaddress:10.6.0.1(no loopback)



Step 1: Establish router adjacencies(cont.)

Router IDHello/dead intervals

NeighborsArea-ID

Router priorityDR IP address

BDR IP addressAuthentication password

Stub area flag

* *

**

* Entry must match on neighboring routers

Hello


Hello

A

D E

CB



Step 2: Electing the DR and BDR (ifnecessary).

P=1 P=0P=1

P=3 P=2

DR BDR

Hello

• The router with the highest priority value is the DR.

• The router with the second highest priority value isthe BDR.

• The default for the interface OSPF priority is 1. Incase of a tie, the router’s router ID is used.



Step 3: Discover routes

On difference network have differ discover process.

On multi-access network, the exchange of routing informationoccurs between the DR or BDR and every other router on thenetwork.

Link partners on a point-to-point or point-to-multipoint networkalso engage in the exchange process.



Exchange Process

Router BNeighbors List

172.16.5.1/24, int E1

172.16.5.1/24E0

I am router ID 172.16.5.2, and I see 172.16.5.1.

Router ANeighbors List

172.16.5.2/24, int E0

172.16.5.2/24E1

I am router ID 172.16.5.1 and I see no one.

Down State

Init State

A B

Two-way State



Step 3: Discover routes (cont.)

I will start exchange because I have router ID 172.16.5.1.

DBD


Here is a summary of my link-state database.

Here is a summary of my link-state database.DBD


E0

172.16.5.1

DR

E0

172.16.5.3

No, I will start exchange because I have ahigher router ID.

Hello


Hello


Exstart State

Exchange State



Step 3: Discover routes (cont.)

Full State

I need the complete entry for network 172.16.6.0/24.

Here is the entry for network 172.16.6.0/24.

Thanks for the information!

LSR


LSAck


LSU


Loading State

E0

172.16.5.1

E0

172.16.5.3

LSAck


Thanks for the information!LSAck


DR



Step 4: Choosing Routes

Topology TableNet Cost Out Interface10.2.2.0 6 To010.3.3.0 7 To010.3.3.0 10 E0

This is the best route to 10.3.3.0.

TokenRing

Cost=10

Cost=6

FDDI

Cost=1

A B C

10.1.1.0/24 10.2.2.0/24 10.3.3.0/24

10.4.4.0/24

St 5 M i t i i R ti



Step 5: Maintaining RoutingInformation

Router A tells all OSPF DRs on 224.0.0.6

xxLSU1

Link-State ChangeDR

AB

St 5 M i t i i R ti





DR tells all others on 224.0.0.5

LSU

2

xx

Link-State Change

LSU1

DR

AB



LSU

3


LSU

2

xx

Link-State Change

LSU1

DR

AB






I need to updatemy routing table.

4

LSU

3

LSU

2

xx

Link-State Change

LSU1

DR

AB





SINGLE AREA OSPFConfiguration



Wildcard Mask



The function of a wildcard mask

A wildcard mask is a 32-bit quantity that isdivided into four octets, with each octetcontaining 8 bits.

A wildcard mask bit 0 means "check thecorresponding bit value“.

A wildcard mask bit 1 means "do not check

(ignore) that corresponding bit value".



Subnet mask and wildcard maskRange ofhost

Subnet mask

-Bit 1 : check-Bit 0 : ignore

Wildcard mask

-Bit 1 : ignore-Bit 0 : check

2 1 1 1 1 1 1 1 0

254

0 0 0 0 0 0 0 1

1

4 1 1 1 1 1 1 0 0

252

0 0 0 0 0 0 1 1

3

8 1 1 1 1 1 0 0 0

248

0 0 0 0 0 1 1 1

7

16 1 1 1 1 0 0 0 0

240

0 0 0 0 1 1 1 1

15

32 1 1 1 0 0 0 0 0

224

0 0 0 1 1 1 1 1

3164 1 1 0 0 0 0 0 0

192

0 0 1 1 1 1 1 1

63

128 1 0 0 0 0 0 0 0

128

0 1 1 1 1 1 1 1

127

256 0 0 0 0 0 0 0 0

0

1 1 1 1 1 1 1 1

255



Common Wildcard mask

Range

of IP

Subnet mask Wildcard mask

2 192.168.1.2

255.255.255.254

192.168.1.2

0. 0 . 0 .1

4 192.168.1.8

255.255.255.252

192.168.1.8

0. 0 . 0 .3

8 192.168.1.16255.255.255.248

192.168.1.160. 0 . 0 .7

16 192.168.1.16

255.255.255.240

192.168.1.16

0. 0 . 0 .15

32 192.168.1.0

255.255.255.224

192.168.1.0

0. 0 . 0 .31

64 192.168.1.128

255.255.255.192

192.168.1.128

0. 0 . 0 .63

128 192.168.1.0

255.255.255.128

192.168.1.0

0. 0 . 0 .127

256 192.168.1.0

255.255.255.0

192.168.1.0

0. 0 . 0 .255



Wildcard any

Any = 0.0.0.0 255.255.255.255



Wildcard host

Host 172.30.16.29 = 172.30.16.29 0.0.0.0



<Output Omitted>

interface Ethernet0ip address 10.64.0.2 255.255.255.0!interface Serial0ip address 10.2.1.2 255.255.255.0<Output Omitted>

<Output Omitted>interface Ethernet0ip address 10.64.1.1 255.255.255.0!<Output Omitted>

router ospf 1

Basic OSPF Configuration

Assign Network with wildcard mask

Broadcast Network Point-to-Point Network

E0

10.64.1.1/24

10.64.1.2/24

E0

S0

10.2.1.2/24

10. 2.1.1/24

S1A B C

network 10.64.1.0 0.0.0.255 area 0 router ospf 50

network 10.2.1.0 0.0.0.255 area 0

network 10.64.0.0 0.0.0.255 area 0



Router#

show ip ospf interface

Verifying OSPF Operation

Displays area ID and adjacency information

Router#

show ip protocols

Verifies that OSPF is configured

Router#

show ip route

Displays all the routes learned by the router



Displays OSPF timers and statistics

Displays information about DR, BDR and neighbors

Displays the link-state database

Verifying OSPF Operation (cont.)

Router#

show ip ospf neighbor detail

Router#

show ip ospf database

Router#

show ip ospf



Allows you to clear the IP routing table

Router#

clear ip route *

Router#

debug ip ospf opt ion

Displays router interaction during the hello,exchange, and flooding processes

Verifying OSPF Operation (cont.)



show ip route



show ip ospf interface

R2#sh ip ospf int e0

Ethernet0 is up, line protocol is up

Internet Address 192.168.0.12/24, Area 0

Process ID 1, Router ID 192.168.0.12, Network Type BROADCAST, Cost: 10Transmit Delay is 1 sec, State DROTHER, Priority 1

Designated Router (ID) 192.168.0.11, Interface address 192.168.0.11

Backup Designated router (ID) 192.168.0.13, Interface address

192.168.0.13

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Hello due in 00:00:04

Neighbor Count is 3, Adjacent neighbor count is 2 Adjacent with neighbor 192.168.0.13 (Backup Designated Router)

Adjacent with neighbor 192.168.0.11 (Designated Router)

Suppress hello for 0 neighbor(s)



show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

192.168.0.13 1 2WAY/DROTHER 00:00:31 192.168.0.13 Ethernet0

192.168.0.14 1 FULL/BDR 00:00:38 192.168.0.14 Ethernet0

192.168.0.11 1 2WAY/DROTHER 00:00:36 192.168.0.11 Ethernet0

192.168.0.12 1 FULL/DR 00:00:38 192.168.0.12 Ethernet0

OSPF over Ethernet - Multiaccess Network

Neighbor ID Pri State Dead Time Address Interface192.168.0.11 1 FULL/ - 00:00:39 10.1.1.2 Serial1

OSPF over HDLC - Point-to-Point Network



EIGRP CONCEPTS



EIGRP Overview

Cisco released EIGRP in 1994 as a scalable, improved version ofits proprietary distance vector routing protocol, IGRP.

Unlike IGRP, which is a classful routing protocol, EIGRPsupports CIDR and VLSM.

Hybrid routing protocol

Fast convergence times

Multiple network-layer protocols supported

Reduced bandwidth usageEasy to configure…



EIGRP and IGRP compatibility

192.168.1.0/24

RTC

EIGRP 2446 IGRP 2446

172.16.1.0/24

10.1.1.0/24

• EIGRP and IGRP automatically redistribute routes betweenautonomous systems with same autonomous system (AS)number.

• IGRP has a maximum hop count of 255. EIGRP has a maximumhop count limit of 224.

RTD

RTA

RTB



Topology Table—AppleTalkDestination 1 Next Router 1/CostDestination 1 Next Router 1/Cost

Topology Table—IPXDestination 1 Next Router 1/CostDestination 1 Next Router 1/Cost

Topology Table—IPDestination 1 SuccessorDestination 1 Feasible Successor

Routing Table—AppleTalkDestination 1 Next Router XDestination 1 Next Router X

Routing Table—IPXDestination 1 Next Router XDestination 1 Next Router X

Routing Table—IPDestination 1 Successor

Neighbor Table—

AppleTalkDestination Next Hop

Router

Neighbor Table—IPXDestination Next Hop

Router

Neighbor Table—IPNext-Hop InterfaceRouter

EIGRP concepts and terminology

EIGRP Successors and Feasible



Network Z

EIGRP Successors and Feasiblesuccessor

RTARTB

I have a routeto Z, with ametric of 5

RTB is successor to Net Z




Network Z


RTARTB

RTC



RTB is successor to Net ZRTC is successor to Net Z




Network Z


RTA

RTX

RTB

RTC

RTY




RTB is successor to Net ZRTB is successor to Net ZRTX is feasible successorto Net Z



(1)

(1)

(1)

(1)

(2)(2)

(a)

A

E

D

C

B

E EIGRP FD AD Topology(a) 3 (fd)

via D 3 2 (Successor)via C 4 3

D EIGRP FD AD Topology(a) 2 (fd)

via B 2 1 (Successor)via C 5 3

C EIGRP FD AD Topology(a) 3 (fd)

via B 3 1 (Successor)via D 4 2 (fs)via E 4 3

DUAL Example (Start)



EIGRP technologies

Many new technologies are improvement in operating efficiency, speed ofconvergence, or functionality relative to others routing protocols.

Four categories:

Neighbor discovery and recovery

Reliable Transport Protocol (RTP)

DUAL finite-state machine algorithm

Protocol-dependent modules (PDM)




EIGRP routers establish adjacencies with neighbor routers by using small hellopackets

On IP networks, EIGRP routers send hellos to the multicast IP address 224.0.0.10

Bandwidth Example link Default hello interval Default hold times

T1 or less Multipoint frame relay, ISDN 60 seconds 180 seconds

Greater than T1 Ethernet, T1 5 seconds 15 seconds




By forming adjacencies, EIGRP routers do:Dynamically learn of new router that join their network

Identify routers that become either unreachable or inoperable

Rediscover routers that had previously been unreachable




EIGRP uses RTP as its own proprietary transport-layer protocol, thatcan guarantee ordered delivery of routing information to all neighbors.

EIGRP can call on RTP to provide reliable or unreliable service as thesituation warrants.

Reliable delivery of other routing information can actually speedconvergence, because EIGRP routers are not waiting for a timer to expirebefore they retransmit.

With RTP, EIGRP can multicast and unicast to different peers

simultaneously, which allows for maximum efficiency.




EIGRP reliable packets are packets that requires explicitacknowledgement:

Update: Send routing updates

Query: Ask neighbors about routing information

Reply: Response to query about routing information

EIGRP unreliable packets are packets that do not require explicitacknowledgement:

Hello: Establish neighbor relationships

ACK: Acknowledgement of a reliable packet

DUAL finite-state machine



Diffusing Update Algorithm (DUAL) is EIGRP's route-calculation engine.

Finite-state machine

– Tracks all routes advertised by neighbors

– Select loop-free path using a successor and remember anyfeasible successors

– If successor lost, use feasible successor

– If no feasible successor, query neighbors andrecomputed new successor

algorithm



DUAL – Discovery route

A B

C

Router B information

Neighbor Table — IP

Router C information

Router B information

Topology Table — IP

Router C information

Successor (primary route)Feasible successor

Routing Table —

IP

Successor (primary route)

DUAL?



Protocol-dependent modules (PDM)

Support for routed protocols, such as IP, IPX, and AppleTalk, isincluded in EIGRP through PDMs.

Easily adapt to new or revised routed protocols, such as IPv6,by adding protocol-dependent modules.

Each PDM is responsible for all functions related to its specific

routed protocol. The IP-EIGRP module is responsible for thefollowing:

Sending and receiving EIGRP packets that bear IP data

Notifying DUAL of new IP routing information that isreceived

Maintaining the results of DUAL routing decisions in the IProuting table

Redistributing routing information that was learned by otherIP-capable routing protocols



CONFIGURING EIGRP



For IP networks

1. router(config)# router eigrp autonomous-system-number

AS mu ch m atch al l router ins ide AS

2. router(config-router)# network network-number

Network n umber only for co nnected m ajor n etwork

3. router(config-if)# bandwidth ki lobi ts

Serial interface link use (if not Router take default)



For IP networks



Verify EIGRP with Show command

Command Description

Show ip eigrp neighbors[int type] [details]

Display EIGRP neighbor table

Show ip eigrp interfaces

[int type] [as-number][details]

Displays EIGRP statistics and status information

Show ip eigrp topology [as-number][ [ip-add] mask ] Display the EIGRP topology table, use the show ip eigrptopology EXEC command. Also used to determine

DUAL states & debug possible DUAL problems.

Show ip eigrp topology[active | pending | zero-successor]

Depending on keywork is used. Display all routes in thetopology table that are either active, pending or withoutsuccessor

Show ip eigrp all-links Display all routes not just FC in EIGRP topology

Show ip eigrp traffic [as-

number]Display the number of EIGRP packets send andreceived.



Verify EIGRP with Debug command

Command Description

Debug eigrp fsm This command helps you observe EIGRP FS activuty andto determine whether route updates are being installed anddeleted by the routing process

debug eigrp packet Displays all types of EIGRP packets, both sent andreceived

debug eigrp neighbor Displays the EIGRP neighbor interaction

debug ip eigrp route Displays advertisements and changes EIGRP makes to therouting table

debug ip eigrp summary Displays a brief report of the EIGRP routing activity

show ip eigrp events Displays the different categories of EIGRP activity,including route calculations

Use show ip eigrp neighbors



p g p gcommand

RTA#show ip eigrp neighbors

IP-EIGRP neighbors for process 400H Address Interface Hold Uptime SRTT RTO Q Seq

(sec) (ms) Cnt Num

1 172.68.2.2 To0 13 02:15:30 8 200 0 9

0 172.68.16.2 Se1 10 02:38:29 29 200 0 613

10



Use show ip route command

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Chapter 06 - OSPF and EIGRP