Single-Area OSPF

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Routers that use link-state routing protocols have the following features:
Routers that use link-state routing protocols have the following features:
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Use the hello information and LSAs received from other routers to build a database about the network  
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*Use the hello information and LSAs received from other routers to build a database about the network.
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Use the SPF algorithm to calculate the shortest route to each network  
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*Use the SPF algorithm to calculate the shortest route to each network.
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Store the route information in the routing table
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*Store the route information in the routing table.
===How routing information is maintained===
===How routing information is maintained===

Revision as of 21:28, 14 September 2006


Link State and Distance Vector Routing Protocols
Protocol Examples Characteristics
Distance Vector RIP v1 & Rip V2
  • Copies Routing table to neightbors
  • Updates frequentlu
  • RIP v1 & v2 use hop count as metric
  • View the network from the perspective of the neighbors
  • Slow to converge
  • Susceptible to routing loops
  • Easy to configure and administer
  • Consumes a lot of bandwith
Link-State OSPF IS-IS
  • Uses shortest path
  • Updates are event triggered
  • Sends Link-state packets to all network routers
  • Has common view of network
  • Fast to converge
  • Not as susceptible to routing loops
  • Harder to configure
  • Requires more memory and processing power than distance vector.
  • Consummes less bandwith than distance vector.

Link State Routing Protocols Features

Link state protocols collect routing data from all other routers in the network or within a defined area of the network. Once the information is collected each router calculates the best paths to all destinations in the network. Each router has it own map of the network so it is less likelly to propagate incorrect information.

The following are some link-state routing protocol functions:

  • Respond quickly to network changes
  • Send triggered updates only when a network change has occurred
  • Send periodic updates known as link-state refreshes
  • Use a hello mechanism to determine the reachability of neighbors.

Each router multicast an hello packets to keep tracks of the state of the nighbor routers. Each router LSAs to keep track of all the routers in its area of the network. The hello packets contain information about the networks that are attached to the router.

Routers that use link-state routing protocols have the following features:

  • Use the hello information and LSAs received from other routers to build a database about the network.
  • Use the SPF algorithm to calculate the shortest route to each network.
  • Store the route information in the routing table.

How routing information is maintained

  • LSAs
  • Topological Database
  • SFP Alogarithm
  • SPF Tree
  • Routing table of paths and ports to determine the best path for packets.

===Link states routing alogarithms




Advantages & Disadvatages of Link State routing
Advantages Disadvantages
  • Fast Convergence times, as changes are reported immediatelly by the source affected
  • It provides robustness againts routing loops
  • Routers known the topology
  • Link-state packets are sequenced and aged
  • The link-state database sizes can be minimized with carefull network design.
  • Significant demands on memory and processing resources
  • Requires very strict network design
  • Requires a knowledgeable network administrator
  • Initial flooding can impede network performance.
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