Routing With a Link-State Protocol

thoughtlessskytopNetworking and Communications

Oct 29, 2013 (3 years and 11 months ago)

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© 2006 Cisco Sy stems, Inc. All rights reserv ed.

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ITE I Chapter 6

1

Routing With a
Link
-
State Protocol


Introducing Routing and Switching in the Enterprise



Chapter 6

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2

Objectives


Describe and plan a network using OSPF.


Design and configure a network using single
-
area
OSPF.


Work with multi
-
protocol environments.


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3

Planning a Network Using OSPF


Link
-
state routing protocol


Open standard developed by IETF


Classless interior gateway protocol


Divides the network into areas for scalability



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Planning a Network Using OSPF


Bandwidth determines the cost of a link


Higher bandwidth = lower cost = desirable route


Cost = 100,000,000 / bandwidth of link in bps


Manual cost configuration at an interface: ip ospf cost


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Planning a Network Using OSPF


SPF algorithm (Diijkstra’s Algorithm)


Each router has a topological tree


SPF tree information stored in topology database

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Planning a Network Using OSPF


Adjacencies: neighbor relationships


Hello protocol


Router ID


Role of loopback interfaces



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Planning a Network Using OSPF


Designated router (DR)


Backup designated router (BDR)


DROther

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Planning a Network Using OSPF


Area 0


Roles of routers in an OSPF Autonomous System:

Area Border Router (ABR)

Autonomous System Border Router (ASBR)



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Design and Configuring a Network Using
Single
-
Area OSPF


OSPF configuration steps:


Enable OSPF + process ID


Advertise networks + wildcard mask and area ID


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Design and Configuring a Network Using
Single
-
Area OSPF



Authentication protects integrity of routing information


Simple password authentication


Message Digest 5 (MD5)




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Design and Configuring a Network Using
Single
-
Area OSPF


Tune OSPF parameters:


Interface priority


Router ID


Loopback and interface addresses


Bandwidth (cost )



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Design and Configuring a Network Using
Single
-
Area OSPF


Verification and troubleshooting commands:


show ip ospf neighbor


show ip protocols, show ip route


show ip ospf, show ip ospf interface



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13

Working with Multi
-
Protocol Environments



Default route configured on ASBR


ASBR distributes the route into the OSPF network



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Working with Multi
-
Protocol Environments


Benefits of OSPF summarization:


Reduces number of networks advertised


Reduces memory requirements


Reduces number of entries in router updates


Isolates flapping and other problems to their location



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Working with Multi
-
Protocol Environments


OSPF limitations:


Increased router memory and processing demands


Strict design requirements


Knowledgable administrator required


Initial discovery process takes up network bandwidth



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Working with Multi
-
Protocol Environments



Administrative distance (AD) determines routes that
appear in routing table




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Summary


OSPF is a classless interior link
-
state routing protocol
used in enterprise networks


OSPF uses bandwidth to generate the cost metric


OSPF routers elect a DR and BDR on multi
-
access
networks


Router ID or router priority can be used to dictate the
selection of DR and BDR


The OSPF network command uses a wildcard mask


Default route distribution and inter
-
area route
summarization are used in OSPF networks


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18