MultiArea OSPF Slides

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Ch

Ch.6

.6 –

– O

OSP

SPF

F

Part 2 of 2: Multi-Area OSPF

CCNP version 3.0

Rick Graziani

Cabrillo College

* Upd

ated

by H

oonJ

ae

Lee

(Dong

seo

Univ.

)

2006. 3. 3

2 2

Note

•

• Optional:

Optional: This lab

This lab coincides with

coincides with my Multi-area OSPF

my Multi-area OSPF Lab

Lab

handout, Rick's OSPF Scenarios (Word doc)

•

• Most of the slides in this presentation do not

Most of the slides in this presentation do not come directly

come directly

from CCNP 1 version 3.0, OSPF, but slides which contain

a little more detail and explanation of OSPF.

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3 3

Optional: Rick’s OSPF Scenarios

Optional: We will be using the following handout for this presentation: Optional: We will be using the following handout for this presentation:

Rick’s OSPF

Rick’s OSPF Handout:Handout: 1.

1. OSPF OSPF Multi-Area Multi-Area -- All NAll Normal ormal AreasAreas 2.

2. OSPF OSPF Multi-Area Multi-Area -- Stub Stub AreaArea 3.

3. OSPF OSPF Multi-Area Multi-Area -- Totally Totally Stubby Stubby AreaArea

This handouts can be downloaded from (Word doc): This handouts can be downloaded from (Word doc):

•

http://www.http://www.cabrillo.cc.ca.us/ciscocabrillo.cc.ca.us/ciscoacad/curracad/curriculum/preiculum/presentations/sesentations/semesmes ter5/OSPF_Scenario_Handout.doc

ter5/OSPF_Scenario_Handout.doc

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Multi Area OSPF

Normal Areas

ASBR ASBR A ABBRR--11 AABBRR--22 Internal Internal Area 51 Area 51 Area 1 Area 1 Area 0 Area 0 172.16.0.0/16 172.16.0.0/16 172.16.1.0/24 172.16.1.0/24 172.16.51.0/24 172.16.51.0/24 172.16.10.4/30 172.16.10.4/30 172.16.20.0/24 172.16.20.0/24 10.1.0.0/24 10.1.0.0/24 11.0.0.0/8 11.0.0.0/8 12.0.0.0/8 12.0.0.0/8 13.0.0.0/8 13.0.0.0/8 .1 .1 .1 .1 ..22 ..33 .5 .5 .6 .6 .1 .1 Lo - RouterID Lo - RouterID 192.168.2.1/32 192.168.2.1/32 Lo - RouterID Lo - RouterID 192.168.1.1/32 192.168.1.1/32 Lo - RouterID Lo - RouterID 192.168.3.1/32 192.168.3.1/32 Pri 100 Pri 100 Pri 200 Pri 200 Lo - RouterID Lo - RouterID 192.168.4.1/32 192.168.4.1/32 Suggestion to Instructors Suggestion to Instructors:: Draw this network on the Draw this network on the white-board as it will be used white-board as it will be used for discussion throughout for discussion throughout these slides.

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Topics

•

AreasAreas

•

LSAsLSAs

•

show ipshow ip ospfospf database database (summary (summary of link of link state dstate database)atabase)

•

shoshow ipw ip rouroutete

•

Stub AreasStub Areas

•

Totally Stubby AreasTotally Stubby Areas

•

E1 and E2 routesE1 and E2 routes

•

Default RoutesDefault Routes

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Route SummarizationRoute Summarization

•

NSSA (Not So Stubby Areas)NSSA (Not So Stubby Areas)

•

Multiple ABR ScenarioMultiple ABR Scenario

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Multiple ASBR ScenarioMultiple ASBR Scenario

•

Virtual LinksVirtual Links

•

Load BalancingLoad Balancing

•

show commandsshow commands

6 6

Issues with large OSPF nets

•

Large link-state tableLarge link-state table

–

– Each router maintains a LSDB for all links in the areaEach router maintains a LSDB for all links in the area –

– The LSDB requires the use of memoryThe LSDB requires the use of memory

•

Frequent SPF calculationsFrequent SPF calculations

–

– A topology change in an area causes each router to re-run SPF toA topology change in an area causes each router to re-run SPF to rebuild the SPF tree and the routing table.

rebuild the SPF tree and the routing table. –

– A flapping link will affect A flapping link will affect an entire area.an entire area. –

– SPF re-calculations are done only for changes within that area.SPF re-calculations are done only for changes within that area.

•

Large routing tableLarge routing table

–

– Typically, the larger the area the larger the routing table.Typically, the larger the area the larger the routing table. –

– A larger routing table requires more memory and takes more time toA larger routing table requires more memory and takes more time to perform the route look-ups.

perform the route look-ups.

Solution

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7 7

OSPF uses “Areas”

•

Hierarchical routing enables you Hierarchical routing enables you to separate large interneto separate large internetworkstworks (autonomous(autonomous systems) into

systems) into smaller internetworkssmaller internetworks that are that are calledcalled areasareas..

•

With this technique, routing still occurs betWith this technique, routing still occurs bet ween the areas (calledween the areas (called inter-areainter-area routing

routing), but many of the smaller internal routing operations, such ), but many of the smaller internal routing operations, such asas recalculating the database –

recalculating the database – re-running the SPF algorre-running the SPF algorithm, are restricted withm, are restricted withinithin an area.

an area.

8 8

•

QuestionQuestion: I understand the routing table is recalculated every time the router: I understand the routing table is recalculated every time the router receives an new version of an LSA. Does OSPF recalculate its

receives an new version of an LSA. Does OSPF recalculate its routing tablerouting table when thei

when their is a topology changr is a topology change in another areae in another area? show ip? show ip ospfospf displadisplays noys no change in SPF ex

change in SPF executioecution, but show ipn, but show ip ospfospf databdatabase shows a changase shows a change in thee in the topology?

topology?

•

AnswerAnswer: Good question! OSPF areas are designed to keep issues : Good question! OSPF areas are designed to keep issues like flappinglike flapping links within an area. SPF is

links within an area. SPF is notnot recalculated if the topology change is inrecalculated if the topology change is in

another area. The interesting thing is that OSPF distributes inter-area (between another area. The interesting thing is that OSPF distributes inter-area (between areas) topology information using a distance-vector method. OSPF uses areas) topology information using a distance-vector method. OSPF uses link-state principles only

state principles only within an areawithin an area. ABRs. ABRs dodo notnot announce topologicalannounce topological information between areas, instead, only routing information is injected into information between areas, instead, only routing information is injected into other areas. ABRs

other areas. ABRs relay routing information between relay routing information between areas via distance vectorareas via distance vector techni

technique similaque similar to RIP or IGRr to RIP or IGRP. This is whP. This is why show ipy show ip ospfospf doesdoes notnot show ashow a change in the number of times SPF has been

change in the number of times SPF has been executed when the topologyexecuted when the topology change is in another area.

change is in another area.

•

NoteNote: It is still a good : It is still a good idea to perform route idea to perform route summarization betweensummarization between areas,areas, announcing multiple routes as a single inter-area route. This

announcing multiple routes as a single inter-area route. This will hide anywill hide any changes in one area from affecting routing tables in

changes in one area from affecting routing tables in other areas.other areas.

An advantage of Multiple Areas

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9 9

OSPF uses “Areas”

10 10

OSPF Router Types

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11 11

OSPF Router Types

Internal

Internal :: Routers with all their Routers with all their interfaces within the same interfaces within the same areaarea Backbone

Backbone

Backbone : Routers with at least one interface connected to : Routers with at least one interface connected to area 0area 0 ASBR

ASBR

ASBR (Autonomous System Boundary Router):(Autonomous System Boundary Router):Routers that have at leastRouters that have at least one interface connected to an external internetwork (another

one interface connected to an external internetwork (another autonomous system)

autonomous system) ABR

ABR

ABR (Area Border Router):(Area Border Router): Routers with interfaces attached to multipleRouters with interfaces attached to multiple areas.

areas.

12 12

OSPF Packet Types

•

Last week we discussed various OSPF packets, used for:Last week we discussed various OSPF packets, used for:

–

– Means for dynamic neighbor discoveryMeans for dynamic neighbor discovery –

– Detect unreachable neighbors within a finite period of Detect unreachable neighbors within a finite period of timetime –

– Ensure two-way communications between neighborsEnsure two-way communications between neighbors –

– Ensure correctness of basic iEnsure correctness of basic interacenterace parameters between neighborsparameters between neighbors –

– Provide necessary information for the election of the DesignatedProvide necessary information for the election of the Designated andand Backup Designated routers on a LAN

Backup Designated routers on a LAN segementsegement –

– Request link state information from another routerRequest link state information from another router –

– Sharing data base summary and Sharing data base summary and detailed informationdetailed information –

– Acknowledge the receipt of an OSPF Acknowledge the receipt of an OSPF packetpacket

OSPF packet types

OSPF Type-2 (DBD)OSPF Type-2 (DBD) OSPF Type-3 (LSR)

OSPF Type-3 (LSR)

OSPF Type-4 (LSU)

OSPF Type-5 (LSAck)

OSPF Type-1 (Hello)

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13 13

OSPF Ty

OSPF Type 4 -

pe 4 - Link St

Link State Adve

ate Advertisem

rtisements

ents

•

• This week we will look at OSPF Type 4 packets more closely

This week we will look at OSPF Type 4 packets more closely

OSPF packet types

14 14

OSPF packet types (Extra)

OSPF Type-4 packets have 7 LSA packets (

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15 15

LSAs

LSAs used for discovering roused for discovering routes and reachinutes and reaching Full State, along withg Full State, along with Maintain Routes Maintain Routes

LSA Types

16 16

LSA Types

LSA Types 1 through 5

•

We will look at tWe will look at these in detail as we discuss hese in detail as we discuss areas in this chapter.areas in this chapter. LSA Type 6

LSA Type 6 MOSPF (Multicast OSPF)MOSPF (Multicast OSPF)

•

NotNot suppsupporteorted by Cisco.d by Cisco.

•

MOSPF enhances OSPF by letting routers use MOSPF enhances OSPF by letting routers use their link-statetheir link-state databases to build multicast distribution trees for the forwarding of databases to build multicast distribution trees for the forwarding of multicast traffic.

multicast traffic.

LSA Type 7

LSA Type 7 NSSA External Link EntryNSSA External Link Entry

•

Originated by anOriginated by an ASBRASBRconnected to anconnected to an NSSANSSA..

•

Type 7 messages can be flooded thrType 7 messages can be flooded throughout NSSAsoughout NSSAs and translatedand translated into LSA Type 5 messages by ABRs.

into LSA Type 5 messages by ABRs.

•

Routes leaRoutes learned via Typerned via Type-7 LSAs-7 LSAs are denoare denoted by eitheted by either a “N1”r a “N1” or andor and “N2”

“N2” in the routing tain the routing table. (Compble. (Compare to E1 and E2).are to E1 and E2).

•

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17 17

Area Types

•

• Standard

Standard

or

or Normal Areas

Normal Areas

–

Backbone

–

Non-Backbone

•

• Stub

Stub

–

Stub Area

–

Totally Stubby Area (TSA)

–

Not-so-stubby-area (NSSA)

18 18

Area Types

    ,, 0

0 , OSPF, OSPF OSPFOSPF



 OSPFOSPF OSPFOSPF

일반영역

일반영역(Standard area):(Standard area):링크링크업데이업데이트와트와경로요경로요약을약을받아들받아들이는이는기본기본영역영역

백본영역

백본영역(Backbone area):(Backbone area):다중영역들다중영역들 서로연결서로연결 연결연결 다른모든영역에다른모든영역에 중간매개중간매개 역할수행역할수행하며하며

영역

영역 이다이다..다른모든다른모든 영역영역들은반드시백본들은반드시백본 영역영역 연결연결되어경로되어경로 정보정보 교환교환해야하며해야하며 백본백본 일반일반 영역

영역들의성질을모두들의성질을모두 갖고있다갖고있다..

스터

스터 영역영역(Stubby area):(Stubby area): 구역에구역에 보내오보내오 정보와같은정보와같은 인터인터네트네트워크외부워크외부경로경로 대한정보를대한정보를

받아들이

받아들이 않으며않으며,, ASAS default route(0.0.0.0/0)default route(0.0.0.0/0) 

 ASAS

,, 0.0.0.0/00.0.0.0/0



NSSA(Not-So-Stubby area):NSSA(Not-So-Stubby area): 7 LSA7 LSA

7 LSA

7 LSA 5 LSA5 LSA

라우터가

라우터가 외부네트외부네트워크워크 향하향하 경로정보경로정보 필요필요 경우경우 이용한다

이용한다..

완전스터비

완전스터비영역영역(TSA, Totally Stubby area):(TSA, Totally Stubby area):다른영역다른영역내부내부에서에서 향하향하 외부외부ASAS경로경로 요약경로를요약경로를

수신하 수신하 않는다않는다..영역외부의네트워크영역외부의네트워크 패킷패킷 전송전송 필요필요 있을경우있을경우 대신에대신에 기본경로를이용하여기본경로를이용하여 전송한다 전송한다.. 영역영역 시스시스 고유고유 영역영역이다이다.. 스터비영역과 스터비영역과 유사하유사하지만지만 유형유형 해당해당하는외부하는외부경로경로 유입유입 허락허락하며하며,,특정특정 유형 유형 경로를유형경로를유형 변환시변환시킨다킨다..

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Multi Area OSPF

Normal Areas

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Routes Received on all OSPF Routers

Overview of Normal A

Overview of Normal Areas –reas – This will all be expThis will all be explained!lained! Receives all routes from within A.S

Receives all routes from within A.S.:.:

•

Within the local area – Within the local area – LSA 1 and LSA 2LSA 1 and LSA 2

•

From other areas (Inter-Area) – From other areas (Inter-Area) – LSA 3, LSA 4, LSA 5LSA 3, LSA 4, LSA 5

Receives all routes from External A.S.’s (External AS means routes not from

Receives all routes from External A.S.’s (External AS means routes not from thisthis

OSPF routing domain):

•

From external AS’s – LSA 5From external AS’s – LSA 5

•

As long as routes are being redistributed by tAs long as routes are being redistributed by t he ASBR (more later)he ASBR (more later) Default Routes

Default Routes

•

Received only ifReceived only if default-information-originatedefault-information-originate command was used (later)command was used (later)

•

IfIf default-information-originatedefault-information-originate commacommand is notnd is not used, then thused, then the defaulte default route

route is notis not receivreceiveded

Pa

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21 21

•

• Your Turn

Your Turn -- In groups

In groups, examine

, examine running-configs

running-configs

•

• Look at

Look at the running-configs

the running-configs for “1.

for “1. OSPF Multi-Areas

OSPF Multi-Areas

-- All No

All Norma

rmal Area

l Areas”

s”

•

• Look at the OSPF network

Look at the OSPF network statements!

statements!

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1. OSPF

1. OSPF Multi

Multi-Areas -

-Areas - All N

All Normal A

ormal Areas

reas

ASBR ASBR

ro

roututer er osospfpf 11

redistribute static redistribute static network 172.16.1.0 0.0.0.255 area 0 network 172.16.1.0 0.0.0.255 area 0 ! ! ip

ip clclasasslslesesss ip

ip route 1route 11.0.01.0.0.0 255.0.0 255.0.0.0 Nu.0.0 Null0ll0 ip

ip route 1route 12.0.02.0.0.0 255.0.0 255.0.0.0 Nu.0.0 Null0ll0 ip

ip route 1route 13.0.03.0.0.0 255.0.0 255.0.0.0 Nu.0.0 Null0ll0

ABR-1 ABR-1 interface FastEthernet0/0 interface FastEthernet0/0 ip ip addreaddress 172.16ss 172.16.1.2 255..1.2 255.255.2255.255.055.0 ip

ip osospfpf prprioioririty 2ty 20000

ro

network 172.16.1.0 0.0.0.255 area 0 network 172.16.1.0 0.0.0.255 area 0 network 172.16.51.0 0.0.0.255 area 51 network 172.16.51.0 0.0.0.255 area 51 ABR-2 ABR-2 interface FastEthernet0 interface FastEthernet0 ip ip addreaddress 172.16ss 172.16.1.3 255..1.3 255.255.255.255.0255.0 ip

ip osospfpf prprioioririty 1ty 10000 !

! ro

network 172.16.1.0 0.0.0.255 area 0 network 172.16.1.0 0.0.0.255 area 0 network 172.16.10.4 0.0.0.3 area 1 network 172.16.10.4 0.0.0.3 area 1 Internal Internal ro

network 172.16.0.0 0.0.255.255 area 1 network 172.16.0.0 0.0.255.255 area 1

ABR contains network

statements for each area

it belongs to, using the

proper area value.

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Understanding LSAs

•

shoshow ipw ip ospospff datdatabaabasese –

– This isThis is notnot the link state database, only athe link state database, only a summarysummary.. –

– It is a tool to help determine It is a tool to help determine what routes are included in the routing table.what routes are included in the routing table. –

– We will look at this output to leWe will look at this output to learn the tool as well as become familiar arn the tool as well as become familiar withwith the different types of LSAs.

the different types of LSAs. –

– To view the link state database use:To view the link state database use: shoshow ipw ip ospospff datdatabaabasese [router|network|…] [router|network|…] 0 1 2 3 0 1 2 3 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 9 0 1 2 7 8 9 0 1 2 3 4 5 6 7 8 3 4 5 6 7 8 9 0 1 2 3 4 5 9 0 1 2 3 4 5 6 7 8 9 0 16 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| LS LS age age | | Options Options | | LS LS type type || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| Link Link State State ID ID || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| Advertising Advertising Router Router || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| LS LS sequence sequence number number || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| LS LS checksum checksum | | length length || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LSA Header LSA Header 24 24

•

LSA 1 LSA 1 –– Router Router LSALSA

•

Generated byGenerated byeach routereach router for each area it belongs to.for each area it belongs to.

•

Describes the states of the links in Describes the states of the links in the area to which this router belongs.the area to which this router belongs.

•

Tells the other routers in the area about itself and its links to adjacent OSPFTells the other routers in the area about itself and its links to adjacent OSPF routers, and “leaf networks.”

routers, and “leaf networks.”

•

Flooded only within the arFlooded only within the area. ea. On multi-access networks, sent On multi-access networks, sent to the DR.to the DR.

•

Denoted by just anDenoted by just an ““OO””in the routing table orin the routing table or ““CC””if the network is directlyif the network is directly connected.

connected.

•

ABR will include a set of LSA 1’s for each ABR will include a set of LSA 1’s for each area it belongs to.area it belongs to.

A A CC D D 2 2 5 5 B B 1

1 5 5 Router A’s LSA 1sRouter A’s LSA 1s

which are flooded to all

other routers in this

area.

“Leaf

“Leaf””networnetworkk

LSA 1

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25 25

LSA 1

-LSA 1 -

Rou

ter Li

nk St

ates

•

When a new LSA 1 is received and installed in the LSDB, the routerWhen a new LSA 1 is received and installed in the LSDB, the router forwards that LSA, using hop-by-hop or asynchronous flooding. forwards that LSA, using hop-by-hop or asynchronous flooding.

•

The LSA is sent out all OSPF inThe LSA is sent out all OSPF interfaces that are in thterfaces that are in the Exchangee Exchange StateState or a higher state.

or a higher state.

•

For interfaces in ExstarFor interfaces in Exstartt or lesser state, the ror lesser state, the router will wait unouter will wait until it is outtil it is out of Exstart. of Exstart. 26 26 0 1 2 3 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | LLS S aagge e | | OOppttiioonns s | | 11 || +-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| Link Link State State ID ID || +-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| Advertising Advertising Router Router || +-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| LS LS sequence sequence number number || +-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS

| LS checksum checksum | | length length || +-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| 0 0 |V|E|B| |V|E|B| 0 0 | | # # links links || +-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Link Link ID ID || +-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| Link Link Data Data || +-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| Type Type | | # # TOS TOS | | metric metric || +-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | | ... | +-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| TOS TOS | | 0 0 | | TOS TOS metric metric || +-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Link Link ID ID || +-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| Link Link Data Data || +-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| ... |

LSA 1

(14)

27 27 ASBR ASBR A ABBRR--11 AABBRR--22 Internal Internal Area 51 Area 51 Area 1 Area 1 Area 0 Area 0 172.16.0.0/16 172.16.0.0/16 172.16.1.0/24 172.16.1.0/24 172.16.51.0/24 172.16.51.0/24 172.16.10.4/30 172.16.10.4/30 172.16.20.0/24 172.16.20.0/24 10.1.0.0/24 10.1.0.0/24 11.0.0.0/8 11.0.0.0/8 12.0.0.0/8 12.0.0.0/8 13.0.0.0/8 13.0.0.0/8 .1 .1 .1 .1 ..22 ..33 .5 .5 .6 .6 .1 .1 Lo - RouterID Lo - RouterID 192.168.2.1/32 192.168.2.1/32 Lo - RouterID Lo - RouterID 192.168.1.1/32 192.168.1.1/32 Lo - RouterID Lo - RouterID 192.168.3.1/32 192.168.3.1/32 Pri 100 Pri 100 Pri 200 Pri 200 Lo - RouterID Lo - RouterID 192.168.4.1/32 192.168.4.1/32

Multi Area OSPF

Normal Areas

LSA 1’s being sent

within Area 0

LSA 1

LSA 1 LSA 1LSA 1

LSA 1

-LSA 1 -

Rou

ter Li

nk St

ates

Multi Area OSPF

Normal Areas

LSA 1’s being sent

within other areas

LSA 1 LSA 1 LSA 1 LSA 1 LSA 1 LSA 1 LSA 1 LSA 1

LSA 1

(15)

Multi Area OSPF

Normal Areas

LSA 1 LSA 1 Originated Originated

LSA 1’s are flooded out

other interfaces within

the same area.

LSA 1

flooded

LSA 1

-LSA 1 -

Rou

ter Li

nk St

ates

30 30

LSA 1

LSA 1 --Router Router Link StaLink Statestes

For Router Links: For Router Links:

•

TheThe Link State IDLink State ID is always the same as theis always the same as the Advertising RouterAdvertising Router

•

Advertising RouterAdvertising Router is the Router ID of the is the Router ID of the router that created this LSA 1router that created this LSA 1

Internal#

Internal#sshhoow w iipp oossppff ddaattaa

OSPF Router with ID (192.168.4.1) (Process ID 1) OSPF Router with ID (192.168.4.1) (Process ID 1)

Router Link States (Area 1)

Router Link States (Area 1) <-<-Note Note the Athe Area!rea!

(

(LSA 1 -LSA 1 - Links in the area Links in the area to which this routo which this router belongs.)ter belongs.)

Link

Link ID ID ADV ADV Router Router Age Age Seq# Seq# Checksum Checksum Link Link countcount 192.168.3.1

192.168.3.1 192.168.3.1 192.168.3.1 898 898 0x80000003 0x80000003 0xCE56 0xCE56 22 192.168.4.1

192.168.4.1 192.168.4.1 192.168.4.1 937 937 0x80000003 0x80000003 0xFD44 0xFD44 33

•

Bottom line:Bottom line: Router Link States (LSA1’s) should display all Router Link States (LSA1’s) should display all thethe RouterIDs

RouterIDs of routers in thaof routers in that area, includint area, including its own.g its own.

•

(16)

31 31

ABR-2#

ABR-2#sshhoow w iipp oossppff ddaattaa

Router Link States (Area 1)

Router Link States (Area 1) <-<-Note Note the Athe Area!rea!

(

(LSA 1 -LSA 1 - Links in the area Links in the area to which this routo which this router belongs.)ter belongs.)

Link

Link ID ID ADV ADV Router Router Age Age Seq# Seq# Checksum Checksum Link Link countcount 192.168.3.1

192.168.3.1 192.168.3.1 192.168.3.1 786 786 0x80000003 0x80000003 0xCE56 0xCE56 22 192.168.4.1

192.168.4.1 192.168.4.1 192.168.4.1 828 828 0x80000003 0x80000003 0xFD44 0xFD44 33

•

Bottom line:Bottom line: Router Link States (LSA1’s) should display all Router Link States (LSA1’s) should display all thethe RouterID

RouterIDss of routers in thaof routers in that area, including its owt area, including its own.n.

•

Rick’s reminder: LSARick’s reminder: LSA 11-> “my-> “my oneonearea”area”

LSA 1

-LSA 1 -

Rou

ter Li

nk St

ates

32 32 A

ABBR-R-2 -2 - shshoow iw ipp rrououtete

172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks 172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks O

O IA IA 172.16.51.1/3172.16.51.1/3 2 2 [110/2] [110/2] via via 172.16.1.2, 172.16.1.2, 00:11:44, 00:11:44, FastEthernet0FastEthernet0

O

O 172.16.20.0/2172.16.20.0/24 4 [110/782] [110/782] via via 172.16.10.6, 172.16.10.6, 00:12:29, 00:12:29, Serial0Serial0

C

C 172.16.10.4/3172.16.10.4/3 0 0 is is directly directly connected, connected, Serial0Serial0 C

C 172.16.1.0/24 172.16.1.0/24 is is directly directly connected, connected, FastEthernetFastEthernet 00 O E2

O E2 11.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEtherne11.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEthernet0t0 O E2

O E2 12.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEtherne12.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEthernet0t0 O E2

O E2 13.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEtherne13.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEthernet0t0 192.168.3.0/32 is subnetted, 1 subnets

192.168.3.0/32 is subnetted, 1 subnets C

C 192.168.3.1 192.168.3.1 is is directly directly connected, connected, Loopback1Loopback1

LSA 1

-LSA 1 -

Rou

ter Li

nk St

ates

•

Denoted by just an “Denoted by just an “OO”” in the in the routing tarouting table, or ble, or a “a “CC””

•

Why is there only just anWhy is there only just an”O””O” for this networfor this network and not the othek and not the otherr networks?

networks? –

(17)

33 33

Your Turn -Discuss in groups (LSA 1s)

•

Using the Using the Multi-area Multi-area OSPF Lab OSPF Lab Handout: Handout: “Lab 1“Lab 1. –. – OSPFOSPF Normal

Normal Areas”Areas” verify these verify these results.results.

•

Look at the link state daLook at the link state database summatabase summary (show ipry (show ip ospfospf

database) commands and the Router Links States (LSA1s) for database) commands and the Router Links States (LSA1s) for each router.

each router.

•

Look at the routing tables (show ipLook at the routing tables (show ip route) and notice the roroute) and notice the routesutes within that router’s area.

within that router’s area.

•

Why do some routers have more than one set of Router Links Why do some routers have more than one set of Router Links

States?

•

WheWhere doere does “shos “show ipw ipospfospfdatadatabasebase””tell yotell you the Rou the RouteruterID.ID.

•

WheWhere doere does “shos “show ipw ipospfospfdatadatabasebase””tell yotell you the Aru the Area.ea.

34 34

•

LSA 2 LSA 2 –– NetworNetwork LSAk LSA

•

Generated by the DRGenerated by the DRon every multi-access networkon every multi-access network

•

Denoted by just anDenoted by just an “O”“O”in the routing table orin the routing table or “C”“C”if the network isif the network is directly connected.

directly connected.

•

Flooded only within the originating areaFlooded only within the originating area..

•

LSA 2’s are in link state database forLSA 2’s are in link state database for allall routers within area, even thoserouters within area, even those routers on not on m

routers on not on multi-access networks or DRulti-access networks or DRss on other multi-accesson other multi-access networks in the same area.

networks in the same area.

•

ABR may include a set of LSA 2s for each ABR may include a set of LSA 2s for each area it belongs to.area it belongs to.

LSA 2

(18)

35 35 0 1 2 3 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| LS LS age age | | Options Options | | 2 2 ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| Link Link State State ID ID ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| Advertising Advertising Router Router ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| LS LS sequence sequence number number ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+

| LS

| LS checksum checksum | | length length ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| Network Network Mask Mask ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| Attached Attached Router Router ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+

| ... |

LSA 2

-LSA 2 -

Net

work L

ink S

tate

s

Multi Area OSPF

Normal Areas

LSA 2 LSA 2

No LSA 2’s for ABR-1

in Area 51, or for

Internal because no

other routers on

multi-access segment. access segment. flooded flooded DR DR DR DR LSA 2 LSA 2 LSA 2 LSA 2 flooded flooded LSA 2 LSA 2 LSA 2 LSA 2

LSA 2

(19)

37 37 A

ASBSBR#R#shshow ow ipip osospfpf dadatata

Net Link States (Area 0) Net Link States (Area 0)

(LSA 2

-(LSA 2 - GenerGenerated by the DRated by the DR))

Link

Link ID ID ADV ADV Router Router Age Age Seq# Seq# Checksum Checksum 172.16.1.2

172.16.1.2 192.168.2.1 192.168.2.1 201 201 0x8000000D 0x8000000D 0xCFE80xCFE8

LSA 2

-LSA 2 -

Net

work L

ink S

tate

s

•

Link IDLink ID 172.16.1172.16.1.2 = IP address of DR o.2 = IP address of DR on MultiAccessn MultiAccess NetworkNetwork

•

ADV RouterADV Router 192.168.2.1 = 192.168.2.1 = Router ID Router ID of DRof DR

•

Bottom line:Bottom line: Net Link States (LSNet Link States (LSA2’s) should displaA2’s) should display the RouterIDy the RouterIDss ofof the DRs

the DRs on all multi-acceon all multi-access networks in the arss networks in the area and their IPea and their IP addresses.

addresses.

•

Rick’s reminder: LSARick’s reminder: LSA 22-> “Ethernet = Layer-> “Ethernet = Layer 22 oor Dr D R”R” 1

1 22

38 38

•

Using the Using the Multi-area Multi-area OSPF Lab OSPF Lab Handout: Handout: “Lab 1“Lab 1. –. – OSPFOSPF Normal

Normal Areas”Areas” verify these verify these results.results.

•

Look at the link state daLook at the link state database summatabase summary (show ipry (show ip ospfospf database) commands and the Net Links States (LSA2s) for database) commands and the Net Links States (LSA2s) for each router.

each router.

•

Look at the routing tables (show ipLook at the routing tables (show ip route) and notice throute) and notice the multi-e multi-access routes within that router’s area.

access routes within that router’s area.

•

Could a router have more than one entry in its listing of Net Could a router have more than one entry in its listing of Net

Links States?

•

Could an area with a broadcast segment, still have no LSA 2’s? Could an area with a broadcast segment, still have no LSA 2’s?

Your Turn -Discuss in groups (LSA 2s)

(20)

39 39

•

LSA 3 –LSA 3 –SummSummary Lary LSASA

•

Originated by theOriginated by theABRABR..

•

Describes links betweenDescribes links between ABRABR andand Internal RoutersInternal Routers of the Local Areaof the Local Area

•

ABR will include a set of LSA 3’s for each area it belongs to.ABR will include a set of LSA 3’s for each area it belongs to.

•

LSA 3s are flooded throughout the backbone (Area 0) and to otherLSA 3s are flooded throughout the backbone (Area 0) and to other

ABRs.

•

Routes learned via LSA type 3Routes learned via LSA type 3s s are denoted by are denoted by anan “IA”“IA”(Inte(Inter-arr-area)ea) inin the routing table.

the routing table.

LSA 3 –

Sum

mar

y Net Li

nk Sta

tes

40 40 0 1 2 3 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| LS LS age age | | OptioOptions ns | | 3 3 oror 4 4 ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| Link Link State State ID ID ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| Advertising Advertising Router Router ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| LS LS sequence sequence number number ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+

| LS

| LS checksum checksum | | length length ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| Network Network Mask Mask || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ | | 0 0 | | metric metric || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+ |

| TOS TOS | | TOS TOS metric metric ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+

| ... |

LSA 3 –

(21)

41 41

LSA 3 –

Sum

mar

y Net Li

nk Sta

tes

Multi Area OSPF

Normal Areas

LSA 1’s are sent as

LSA 3’s into other

areas by the ABRs.

LSA 1

LSA 3

LSA 3 LSA 3LSA 3

LSA 1

LSA 3 –

(22)

Multi Area OSPF

Normal Areas

LSA 1’s are sent as

LSA 3’s into other

areas by the ABRs.

LSA 1 LSA 1 LSA 1 LSA 1 LSA 1 LSA 1 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 1 LSA 1 LSA 3 LSA 3 LSA 3 LSA 3

LSA 3 –

Sum

mar

y Net Li

nk Sta

tes

Multi Area OSPF

Normal Areas

LSA 1 LSA 1 LSA 1 LSA 1 LSA 1 LSA 1 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 1 LSA 1 LSA 3 LSA 3 LSA 3 LSA 3 Area 1 Area 1

LSA 1’s are sent as LSA 3’s

into other areas by the

ABRs.

•

Routers only see the topology of the area they belong Routers only see the topology of the area they belong to.to.

•

When a link in one area changes, the adjacent routers originate in LSA 1’s andWhen a link in one area changes, the adjacent routers originate in LSA 1’s and flood them within the area, causing intra-area (internal) routers to re-run the flood them within the area, causing intra-area (internal) routers to re-run the SPF and recalculating the routing table.

SPF and recalculating the routing table.

•

ABRsABRs do notdo not announannounce topologice topological informcal information betwation between areas.een areas.

•

ABRsABRs only inject routing information into only inject routing information into other areas, which is baother areas, which is basically asically a distance-vector technique.

(23)

Multi Area OSPF

Normal Areas

LSA 1’s are sent as LSA

3’s into other areas by the

ABRs. ABRs. LSA 1 LSA 1 LSA 1 LSA 1 LSA 1 LSA 1 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 3 LSA 1 LSA 1 LSA 3 LSA 3 LSA 3 LSA 3 Area 1 Area 1

•

ABRsABRs calculate intra-area routes fcalculate intra-area routes for directly attached areas anor directly attached areas and announced announce them to all other areas as inter-area routes, using LSA 3’s.

them to all other areas as inter-area routes, using LSA 3’s.

•

OSPF ABRsOSPF ABRs will only announce inter-will only announce inter-area routes that were area routes that were learned from thelearned from the backbone area, area 0.

backbone area, area 0.

•

The backbone area serves as a repository for The backbone area serves as a repository for inter-area routes.inter-area routes.

•

This keeps OSPF safe from routing loops.This keeps OSPF safe from routing loops.

Don’t forget about the LSA

1’s from Area 0.

Multi Area OSPF

Normal Areas

LSA 1 LSA 1 LSA 1 LSA 1 LSA 3 LSA 3 LSA 3 LSA 3 LSA 1 LSA 1

LSA 3 –

(24)

47 47 Area 0 Area 0 Backbone Area Backbone Area Area 51 Area 51 Area 1 Area 1 R RTTAA RRTTBB RTC RTC L LSSAA33 LLSSAA33

Normal Areas

LSA 1’s LSA 1’s Not ABR Not ABR

•

ABRsABRs calculate intra-arcalculate intra-area routes for directly attachea routes for directly attached areas anded areas and announce them to all other areas as inter-area routes, using LSA 3’s. announce them to all other areas as inter-area routes, using LSA 3’s.

•

In normal operation,In normal operation, OSPF ABRsOSPF ABRswill only announcwill only announce inter-are inter-area ea

routes that were learned from the backbone area, area 0

routes that were learned from the backbone area, area 0 ..

•

RTC does not forward LSA 3’s from Area 1 to Area 51, and does notRTC does not forward LSA 3’s from Area 1 to Area 51, and does not forward LSA 3’s from Area 51 to Area 1.

forward LSA 3’s from Area 51 to Area 1.

•

The backbone area serves as a repository for inter-area routes.The backbone area serves as a repository for inter-area routes.

•

This keeps OSPF safe from routing loops.This keeps OSPF safe from routing loops.

48 48 Area 0 Area 0 Backbone Area Backbone Area Area 51 Area 51 Area 1 Area 1 R RTTAA RRTTBB RTC RTC LSA 3 LSA 3 LSA 3 LSA 3

Normal Areas

LSA 1’s LSA 1’s Not ABR Not ABR

•

Example of an LSA 1 originated in Area 1, sent to Area 0 as an LSA 3,Example of an LSA 1 originated in Area 1, sent to Area 0 as an LSA 3, and the sent to Area 51 as an LSA 3.

and the sent to Area 51 as an LSA 3.

•

RTC does not forward the LSA 3’s back into Area 1RTC does not forward the LSA 3’s back into Area 1, or routing, or routing loops may develop.

loops may develop.

•

Again, in normal operAgain, in normal operations, OSPF ABRsations, OSPF ABRs will only announce intewill only announce inter-arear-area routes that were learned from the backbone area, area 0.

routes that were learned from the backbone area, area 0.

•

Note: RTC will create LSA 1’s and flood them within the appropriateNote: RTC will create LSA 1’s and flood them within the appropriate area.

(25)

49 49 Area 0 Area 0 Backbone Area Backbone Area Area 51 Area 51 Area 1 Area 1 R RTTAA RRTTBB RTC RTC

Normal Areas

LSA 1’s

LSA 1’s LSA 1’sLSA 1’s

LSA 3

LSA 3 LSA 3LSA 3

LSA 3 LSA 3 LSA 3 LSA 3 Not ABR Not ABR

•

RTC does notRTC does notforward Lforward LSA 1’s from Area 1 as LSA 3’s into ASA 1’s from Area 1 as LSA 3’s into Area 51.rea 51.

•

RTC does notRTC does notforward Lforward LSA 1’s from Area 51 aSA 1’s from Area 51 as LSA 3’s into Area 1.s LSA 3’s into Area 1.

•

Any LSA 3’s from RTC are not forwarded into Area 0 by RTA or RTB.Any LSA 3’s from RTC are not forwarded into Area 0 by RTA or RTB.

•

OSPF specification stateOSPF specification states that ABRss that ABRs are restricted to considare restricted to considering LSAering LSA 3’s only from the backbone area to avoid routing information loops. 3’s only from the backbone area to avoid routing information loops.

Normal Areas

LSA 1’s LSA 1’s LSA 3 LSA 3 LSA 3 LSA 3

X

Area 1 routers re-run

SPF, creates new SPF

tree and updates

routing table.

Update is sent to Area 0 and Area

51 routers using a “distance

vector upd

vector update technate technique.”ique.”SPF notSPF not

re-run, but routers update routing

table.

Topology Change: Down Link

•

When a router deteWhen a router detects a topology change it immediatcts a topology change it immediately sends outely sends out LSALSA 1’s (Router LSAs) with the change.

1’s (Router LSAs) with the change.

•

In the case of a down link, thIn the case of a down link, the age of the LSA is set to MaxAge age of the LSA is set to MaxAgee (3,600(3,600 seconds) –

seconds) – Routers Routers that recethat receive LSAsive LSAs with the with the age eqage equal to Mual to MaxAgeaxAge remove this entry from their LSDB (Link State Data Base).

remove this entry from their LSDB (Link State Data Base).

•

Routers that receive the LSA 1’s, within the area of the change, re-runRouters that receive the LSA 1’s, within the area of the change, re-run their SPF algorithm, to build a new SPF tree and then make the

their SPF algorithm, to build a new SPF tree and then make the changes to

(26)

Normal Areas

LSA 1’s LSA 1’s LSA 3 LSA 3 LSA 3 LSA 3

X

Area 1 routers re-run

SPF, creates new SPF

tree and updates

routing table.

Update is sent to Area 0 and Area

51 routers using a “distance

vector upd

vector update technate technique.”ique.”SPF notSPF not

re-run, but routers update routing

table.

Topology Change: Down Link Topology Change: Down Link

•

ABR RTA receives the LSA 1 and recalculate their SPF for that area,ABR RTA receives the LSA 1 and recalculate their SPF for that area, Area 1.

Area 1.

•

RTA floods the change as a LSA 3 within its other area, Area 0.RTA floods the change as a LSA 3 within its other area, Area 0.

•

RTB receives the LSA 3 and floods it within Area 51.RTB receives the LSA 3 and floods it within Area 51.

•

Area 0 and Area 51 routers do not recalculate their SPFs, but inject theArea 0 and Area 51 routers do not recalculate their SPFs, but inject the change into their routing tables.

change into their routing tables. Note

Note: LSA 3’s (and other Inter-Ar: LSA 3’s (and other Inter-Area routes) are vieweea routes) are viewed as “leaf nodes”d as “leaf nodes” inin the SPF tree.

the SPF tree.

52 52

Multi Area OSPF

Normal Areas

ASBR ASBR A ABBRR--11 AABBRR--22 Internal Internal Area 51 Area 51 Area 1 Area 1 Area 0 Area 0 172.16.0.0/16 172.16.0.0/16 172.16.1.0/24 172.16.1.0/24 172.16.51.0/24 172.16.51.0/24 172.16.10.4/30 172.16.10.4/30 172.16.20.0/24 172.16.20.0/24 10.1.0.0/24 10.1.0.0/24 11.0.0.0/8 11.0.0.0/8 12.0.0.0/8 12.0.0.0/8 13.0.0.0/8 13.0.0.0/8 .1 .1 .1 .1 ..22 ..33 .5 .5 .6 .6 .1 .1 Lo - RouterID Lo - RouterID 192.168.2.1/32 192.168.2.1/32 Lo - RouterID Lo - RouterID 192.168.1.1/32 192.168.1.1/32 Lo - RouterID Lo - RouterID 192.168.3.1/32 192.168.3.1/32 Pri 100 Pri 100 Pri 200 Pri 200 Lo - RouterID Lo - RouterID 192.168.4.1/32 192.168.4.1/32

LSA 3 –

(27)

53 53

ASBR

A

ASBSBR# sR# shohow ipw ip osospfpf dadatatababasese

Summary Net Link States (Area 0) Summary Net Link States (Area 0) Link

Link ID ID ADV ADV Router Router Age Age Seq# Seq# ChecksumChecksum

(Area 1

(Area 1 networks -networks - Advertising Router Advertising Router ABR-2)ABR-2)

172.16.10.4

172.16.10.4 192.168.3.1 192.168.3.1 278 278 0x80000001 0x80000001 0xD1260xD126 172.16.20.0

172.16.20.0 192.168.3.1 192.168.3.1 278 278 0x80000001 0x80000001 0xA7460xA746

(Area 51

(Area 51 networks -networks - Advertising Router Advertising Router ABR-1)ABR-1)

172.16.51.1

172.16.51.1 192.168.2.1 192.168.2.1 206 206 0x80000005 0x80000005 0xA8320xA832

LSA 3 –

Sum

mar

y Net Li

nk Sta

tes

•

Link IDLink ID = IP network addresses of networks in other areas= IP network addresses of networks in other areas

•

ADV RouterADV Router = = ABR Router ABR Router ID sending the ID sending the LSA-3LSA-3

•

Divided by ABRDivided by ABR

•

Bottom line:Bottom line: Should see networks in other areas and the ABR advertising thatShould see networks in other areas and the ABR advertising that route.

route.

•

Rick’s reminder: LSARick’s reminder: LSA 33-> -> “n“netetworworks ks sesent nt by by ththe Ae A BB R”R” 1 1 2 2 33 54 54

ASBR

ASB

ASBR# shR# show ipow ip rouroutete

172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks 172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks

O

O IA IA 172.16.51.1/32 172.16.51.1/32 [110/2] [110/2] via via 172.16.1.2, 172.16.1.2, 00:02:54, 00:02:54, FastEthernet0/0FastEthernet0/0 O

O IA IA 172.16.20.0/24 172.16.20.0/24 [110/783] [110/783] via via 172.16.1.3, 172.16.1.3, 00:02:54, 00:02:54, FastEthernet0/0FastEthernet0/0 O

O IA IA 172.16.10.4/30 172.16.10.4/30 [110/782] [110/782] via via 172.16.1.3, 172.16.1.3, 00:02:54, 00:02:54, FastEthernet0/0FastEthernet0/0

C

C 172.16.1.0/24 172.16.1.0/24 is is directly directly connected, connected, FastEthernet0/0FastEthernet0/0 10.0.0.0/24 is subnetted, 1 subnets

10.0.0.0/24 is subnetted, 1 subnets C

C 10.1.0.0 10.1.0.0 is is directly directly connected, connected, FastEthernet0/1FastEthernet0/1 S

S 11.0.0.0/8 11.0.0.0/8 is is directly directly connected, connected, Null0Null0 S

S 12.0.0.0/8 12.0.0.0/8 is is directly directly connected, connected, Null0Null0 192.168.1.0/32 is subnetted, 1 subnets 192.168.1.0/32 is subnetted, 1 subnets C

C 192.168.1.1 192.168.1.1 is is directly directly connected, connected, Loopback0Loopback0 S

S 13.0.0.0/8 13.0.0.0/8 is is directly directly connected, connected, Null0Null0

LSA 3 –

Sum

mar

y Net Li

nk Sta

tes

•

Routes learned via LSA type 3Routes learned via LSA type 3s s are denoted by are denoted by an “an “IAIA”” (Inte(Inter-Ar-Arearea Routes) in the routing table.

(28)

55 55

Another example:

Another example: non-area 0 non-area 0 router, Internalrouter, Internal

In

Inteternrnalal# s# shohow ipw ip osospfpf dadatatababasese

LSA 3

-LSA 3 - Generated by Generated by the ABR. the ABR. Describes linkDescribes links between ABs between ABR andR and Internal Routers of the Local Area

Internal Routers of the Local Area

(Area 51 networks

-(Area 51 networks - AdvertisAdvertising Router ABR-2)ing Router ABR-2)

Summary Net Link States (Area 1) Summary Net Link States (Area 1)

Link

Link ID ID ADV ADV Router Router Age Age Seq# Seq# ChecksumChecksum 172.16.1.0

172.16.1.0 192.168.3.1 192.168.3.1 848 848 0x80000005 0x80000005 0xD3390xD339 172.16.51.1 192.168.3.1 843

172.16.51.1 192.168.3.1 843 0x80000001 0x80000001 0xB3290xB329

Internal#

Internal# shshow ow ipip roroututee

172.16.0.0/16 is variably subnetted, 4 subnets, 3 172.16.0.0/16 is variably subnetted, 4 subnets, 3 masksmasks

O

O IA IA 172.16.51.1/32 172.16.51.1/32 [110/783] [110/783] via via 172.16.10.5, 172.16.10.5, 00:13:48, 00:13:48, Serial0Serial0

C

C 172.16.20.0/24 172.16.20.0/24 is is directly directly connected, connected, FastEthernet0FastEthernet0 C

C 172.16.10.4/30 172.16.10.4/30 is is directly directly connected, connected, Serial0Serial0

O

O IA IA 172.16.1.0/24 172.16.1.0/24 [110/782] [110/782] via via 172.16.10.5, 172.16.10.5, 00:13:53, 00:13:53, Serial0Serial0

192.168.4.0/32 is subnetted, 1 subnets 192.168.4.0/32 is subnetted, 1 subnets C

C 192.168.4.1 192.168.4.1 is is directly directly connected, connected, Loopback0Loopback0 O E2

O E2 11.0.0.0/8 [110/20] via 172.16.10.5, 00:14:41, Serial011.0.0.0/8 [110/20] via 172.16.10.5, 00:14:41, Serial0 O E2

O E2 12.0.0.0/8 [110/20] via 172.16.10.5, 00:14:41, Serial012.0.0.0/8 [110/20] via 172.16.10.5, 00:14:41, Serial0 O E2

O E2 13.0.0.0/8 [110/20] via 172.16.10.5, 00:14:42, Serial013.0.0.0/8 [110/20] via 172.16.10.5, 00:14:42, Serial0

56 56

•

• Using the Multi-area

Using the Multi-area OSPF Lab

OSPF Lab Handout:

Handout: “Lab 1. –

“Lab 1. –

OSPF Norma

OSPF Normal Areas”

l Areas” verify the

verify these results

se results..

•

• Look at the link state database summary (show ip

Look at the link state database summary (show ip

ospf

ospf database) c

database) commands an

ommands and the

d the Summary Net

Summary Net

Links States (LSA3s) for each router.

•

• Look at the

Look at the routing tables

routing tables (show ip

(show ip route) and notice

route) and notice

the Int

the Interare

erarea

a (IA) rou

(IA) routes.

tes.

•

• Why do some routers have more than one set of

Why do some routers have more than one set of

Summary Net Links States?

Your Turn -Discuss in groups (LSA 3s)

(29)

57 57

•

• LSA 4 –

LSA 4 –

ASBR S

umma

ry LSA

•

• Originated by the ABR

Originated by the ABR..

•

• Flooded throughout the backbone area to the

Flooded throughout the backbone area to the other

other

ABRs

ABRs..

•

• Describes the

Describes the reach

reach

abili

ability

ty

to the A

SBRs

•

• Advertises an ASBR (Router ID) not a network

Advertises an ASBR (Router ID) not a network

•

• Included in routing table as an “

Included in routing table as an “IA

IA”” ro

rout

ute.

e.

•

• Same f

Same format a

ormat as a LSA

s a LSA 3 -

3 - Summa

Summary LSA

ry LSA, exce

, except LSA 4

pt LSA 4

ASBR Summary LSA the Network Mask field is always 0

Exceptions

•

• Not

Not

flooded to Stub and Totally

Stubby networks.

•

• More on this later

More on this later

LSA 4

–

ASBR

Summar

y Link

States

58 58 0 1 2 3 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| LS LS age age | | OptiOptions ons | | 3 3 oror 4 4 || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| Link Link State State ID ID || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| AdvertisinAdvertising g Router Router || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| LS LS sequence sequence number number || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| LS

| LS checksum checksum | | length length || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| Network Network Mask Mask ||

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | 0 0 | | metric metric || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |

| TOS TOS | | TOS TOS metric metric || +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| ... |

LSA 4