Module 3 : OSPF Part2

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Oct 29, 2013 (3 years and 7 months ago)

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Module 3 : OSPF


Part2

By Sang Gon Lee


Spring 2009

Contents

3.6 Multiarea OSPF Operation


Large OSPF Network Issues



With single area



calculations



Large routing



Large LSDB



Hierarchical area



Reduced frequency of SPF calculations

-

isolate route flapping



Smaller routing tables



Reduced LSU overhead


Question
: I understand the routing table is recalculated every time the router
receives an new version of an LSA.
Does OSPF recalculate its routing table
when their is a topology change in another area?

show ip ospf displays no
change in SPF execution, but show ip ospf database shows a change in the
topology?



Answer
: Good question! OSPF areas are designed to keep issues like flapping
links within an area.
SPF is
not

recalculated if the topology change is in
another area. The interesting thing is that OSPF distributes inter
-
area (between
areas) topology information using a distance
-
vector method.

OSPF uses link
-
state principles only within an area
.
ABRs do
not

announce topological
information between areas, instead, only routing information is injected into
other areas. ABRs relay routing information between areas via distance vector
technique similar to RIP or IGRP
. This is why show ip ospf does
not

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


Note
: It is still a good idea to perform route summarization between areas,
announcing multiple routes as a single inter
-
area route. This will hide any
changes in one area from affecting routing tables in other areas.

An advantage of Multiple Areas
-
FYI

OSPF LSA Types


OSPF LSA Types(
계속
)

OSPF LSA Types(
계속
)

OSPF LSA Types(
계속
)

OSPF LSA Types(
계속
)

OSPF LSA Types(
계속
)

LSA type

source

Flooding
범위





Link State
ID

1 (router LSA)

지역

router

Area
내부

직접

연결된

링크

이웃

router

2 (Network LSA)

DR

Area
내부

내부

네트워크를

구성
하는



router

IP of DR

3(summary LSA)

ABR

AS
내부
,

ABR


지역간

전파

지역

내의

소유

네트워

,
자동요약

안됨
.

network
number

4(summary LSA)


ABR

AS
내부
,

ABR


지역간

전파


ASBR


보내



type1 LSA

ASBR
라우터

ID

5(Extenal LSA)

ASBR

AS
내부
,

ABR


지역간

전파

routes to networks
outside the OSPF
autonomous system.

외부

네트워크

number

Interpreting the OSPF LSDB and Routing Table



Link ID: Identifies each LSA.


ADV Router: Advertising router


Age: The age in sec, maximum
age : 3,600 sec.


Seq#: Sequence number of the
LSA.


Checksum: Checksum of the
individual LSA .


Link count: Total number of
directly attached links,

Interpreting the Routing Table


OSPF LSA Types(
계속
)


Type 6


Multicast OSPF


Type 7


used in not
-
so
-
stubby areas (NSSAs),


originated by ASBRs, NSSA


한정


Type 8


used in internetworking OSPF and


Border Gateway Protocol (BGP)


Types 9, 10, 11
-

opaque LSAs,
향후

업그레이드용

Calculating Costs for E1 and E2 Routes



외부경로

타입

E1

:
다수의

ASBR
들이

외부경로를

동일

자치

시스템에

홍보할


.


외부경로

타입

E2

:
오직



개의

ASBR


자치

시스템에

외부
경로를

홍보할


.

Configuring OSPF LSDB Overload Protection


Changing the Cost Metric



Cost = 100 Mbps / (bandwidth in Mbps).

3.7 Stub, Totally Stubby, and
Not
-
So
-
Stubby Areas


Configuring OSPF Area Types


OSPF Area Types


Standard area
:
모든

종류의

LSA


수신
.(default).





Backbone area (transit area):

area


경로

정보

교환





Stub area
:


-

AS
외부

경로는

받지

않음
.


-

Type 4 and 5 LSAs are blocked, default
경로



알려


.



Totally stubby area
:


-

외부

AS
경로와

다른

area


summary routes
받지

않음
.


-

blocks type 4 and 5 LSAs as well as all summary LSAs (type 3)


-

Type 3 LSA (advertise the default route)


제외
.



Not
-
so
-
stubby area
:


-

외부

경로

유입

허용
.


-

ASBR Type 7 LSAs


flood

ABR. Type 5 LSA


AS
전파


Stub and Totally Stubby Areas Rules

Configuring Stub Area


OSPF Stub Area Configuration Example


Configuring Totally Stub Areas


Totally Stubby Area Configuration Example


Interpreting Routing Tables


Interpreting Routing Tables(
계속
)

Interpreting Routing Tables(
계속
)

Interpreting Routing Tables(
계속
)


No O IA code.


Configuring Not
-
So
-
Stubby Areas


NSSA :
제한된

형태로

외부경로

정보를

stub area


유입시킨다
.


Type 7 LSA in the routing table :



O N1 : an external type 1 metric



O N2 : an external type 2 metric



N stands for NSSA.



The default is O N2.


ASBR :
외부

routes


받아

들인다

Type 7
으로

redistribute.


ABR : Type 7


Type 5


변환하여

area 0


주입
.
요약한다
.

Configuring Not
-
So
-
Stubby Areas


Configuring Not
-
So
-
Stubby Areas

Configuring Not
-
So
-
Stubby Area Example



Configuring an NSSA Totally Stubby Area Example


Verifying All Stub Area Types


3.8 Virtual Links


OSPF Virtual Links



Hello : 10sec


LSA : does not age out


Configuring Virtual Links


Verifying a Virtual Link Configuration


3.9 Route Summarization

ABR and ASBR Implementation


area


route



ABR



연속적

서버





AS


route



ASBR



연속적

서버




OSPF Route Summarization Example


Configuring OSPF Route Summarization


Configuring Route Summarization at ABR



확인

해보기

Configuring Route Summarization at ASBR


Benefits of a Default Route in OSPF



디폴트

경로를

표준

area


홍보하는

방법

2
가지



(1) advertise 0.0.0.0 into the OSPF domain


홍보하는

router


이미

default route


라우팅

테이블에

가지고

있어야


.



(2) advertise 0.0.0.0 (default route
유무에

관계없이
)




default

info牭ation origination
command

Configuring a Default Route in OSPF



보통
:
디폴터

라우터가

라우팅

테이블에

있을때
, 〮〮〮〠
디폴터

홍보


Always :
디폴터

경로가

없더라도

〮〮〮〠
디폴터

홍보




Metric type : external type 1
혹은


디폴터는



Example of Configuring a Default Route in OSPF



multihomed to dual Internet service providers (ISPs).


Provider A : preferred, provider B : backup.

3.10 OSPF Authentication



OSPF Authentication Methods



Simple password authentication


(also called plain
-
text authentication)






Message Digest (MD) 5 authentication

OSPF Authentication Methods

Ex. Configuring Simple Password Auth.

Configuring MD5 Authentication



A key and key ID must be configured on each router.



Key
정의


인증방법

설정

-

MD5

Example of Configuring MD5 Authentication


Troubleshooting Simple Password
Authentication


Troubleshooting Simple Password
Authentication

Troubleshooting MD5 Authentication


Troubleshooting MD5 Authentication