ca_ex_s2m10_link-state routing protocol.ppt [compatibility mode]

8/3/2019 CA_Ex_S2M10_Link-State Routing Protocol.ppt [Compatibility Mode]

http://slidepdf.com/reader/full/caexs2m10link-state-routing-protocolppt-compatibility-mode 1/34

Chapter 10: Link-State Routing

Protocols

CCNA Ex loration version 4.0



Objectives

• Describe the basic features & concepts of link-staterouting protocols.

• List the benefits and requirements of link-state routingprotocols.

Hc vin mng Bach Khoa - Website: www.bkacad.com 2



Link-State Routing




Link-State Routing Protocols

• Link state routing protocols

– Also known as shortest path first algorithms

– Built around Dijkstra’s SPF




Introduction to the SPF Algorithm

• Dikjstra’s algorithm also known as theshortest path first (SPF) algorithm. This

algorithm accumulates costs along eachpath, from source to destination.


destination in the topology.




• The shortest path to a destination is not necessarilythe path with the least number of hops




Link-State Routing Process

• How routers using Link State Routing Protocols reach convergence


. .

2. Link state routers exchange hello packet to “meet” other directlyconnected link state routers.

3. Each router builds its own Link State Packet (LSP) whichincludes information about neighbors such as neighbor ID, linktype, & bandwidth.

4. After the LSP is created the router floods it to all neighbors whothen store the information and then forward it until all routershave the same information.

5. Once all the routers have received all the LSPs, the routers thenconstruct a topological map of the network which is used to

determine the best routes to a destination.



• Link: this is an interface on arouter

• Information about the state of

those links is known as link-states.This informationincludes:

– The interface's IP addressand subnet mask.

1.Learning about Directly Connected Network


– The type of network, suchas Ethernet (broadcast) orSerial point-to-point link.

– The cost of that link.

– Any neighbor routers onthat link.



2.Sending Hello Packets to Neighbors


• Routers with link-state routing protocols use a Helloprotocol to discover any neighbors on its links. Aneighbor is any other router that is enabled with thesame link-state routing protocol.



• When 2 link-state routers learn that they areneighbors, they form an adjacency.

• These small Hello packets continue to beexchanged between two adjacent neighborswhich serve as a "keepalive" function to monitor



.

• If a router stops receiving Hello packets from aneighbor, that neighbor is consideredunreachable and the adjacency is broken.



• Each router builds its own Link State

Packet (LSP).• Contents of LSP:

3.Building the Link-State Packet


. link

2. Includes information about

neighbors such as neighbor ID,link type, & bandwidth.



3.Building the Link-State Packet




4.Flooding Link-State Packets to Neighbors

• Each router floods the LSP to all neighbors,who then store all LSPs received in a

database.• Each router floods its link-state information

-


area.

• Whenever a router receives an LSP from aneighboring router, it immediately sends thatLSP out all other interfaces except theinterface that received the LSP.




• LSPs are sent out under the followingconditions

1. During initial startup of the router orof the routing protocol process on


2. Whenever there is a change in the

topology, including a link going

down or coming up, or a neighboradjacency being established orbroken




• Unlike distance vector routing protocolsthat must first run the Bellman-Ford

algorithm to process routing updates before sending them to other routers, link-state


algorithm after the flooding is complete.

• As a result, link-state routing protocols

reach convergence much faster thandistance vector routing protocols.



5.Constructing a link state database

• Each router uses the database to constructa complete map of the topology and

computes the best path to each destinationnetwork.




• Each router in the topology determinesthe shortest path from its ownperspective.





Shortest Path First (SPF) Tree

ignore


• Building a portion of the SPF

tree:Process begins by examiningR2’s LSP informationR1 ignores 1st LSP: R1 alreadyknows it’s connected to R2





• Building a portion of the SPFtree:

R1 uses 2nd LSPReason: R1 can create a linkfrom R2 to R5. This informationis added to R1’s SPF tree





• Building a portion of the SPF

tree:R1 uses 3rd LSP

Reason: R1 learns that R2is connected to 10.5.0.0/16.

This link is added to R1’s

SPF tree.




• Determining the shortestpath

– The shortest path to a


est nat on eterm neby adding the costs &finding the lowest cost




• Once the SPF algorithm hasdetermined the shortest pathroutes, these routes areplaced in the routing table.




ImplementingLink-State Routing Protocols




Routingprotocol

BuildsTopological

map

Router canindependentlydetermine the

shortest path toConvergence

A periodic/ event driven

routing updates

Useof

LSP

Advantages of a Link-State Routing Protocol


Distancevector

No No Slow Yes/Yes No

Link State Yes Yes Fast No/Yes Yes



Advantages of a Link-State Routing Protocol




• Memory requirements

– Typically link state routing protocols usemore memory

• Processing Requirements

Requirements for using a link state routing protocol


– More CPU processing is required of linkstate routing protocols

• Bandwidth Requirements

– Initial startup of link state routing protocolscan consume lots of bandwidth





• Modern LSR protocols are designed to minimize the effects onmemory, CPU, and bandwidth. Multiple areas can reduce the size ofthe link-state databases. It limits the amount of link-state informationflooding in a routing domain and send LSPs only to those routers that

need them.




• 2 link state routing protocols used for routing IP – Open Shortest Path First (OSPF) – Intermediate System-Intermediate System (IS-IS)

Hc vin mng Bach Khoa - Website: www.bkacad.com 32Multi-areas OSPF and IS-IS are discussed in CCNP



Summary


ca_ex_s2m10_link-state routing protocol.ppt [compatibility mode]

Documents