CCNA 3.6: Compare and contrast distance-vector and link-state routing protocols


Dynamic routing protocols are categorized as either distance-vector protocols or link-state protocols


Study Notes:

Distance-Vector Routing Protocols

  • The full routing table is sent in periodic updates to neighbors, which requires more bandwidth
  • Distance is the main metric used to calculate routes
    • RIP uses hop count
    • IGRP uses bandwidth and delay
  • Slower to converge because it has to wait for the periodic updates
  • More susceptible to loops
  • Distance-Vector Protocols - RIP, IGRP
  • Routers rely on neighbors for route information - routing by rumor


Link-State Routing Protocols

  • Created to avoid the convergence and loop issues of Distance-Vector protocols
  • Routers send updates that advertise the state of their links. The full routing table is not sent, which saves on bandwidth.
  • Cost is the metric used to calculate routes
  • Areas are used to define which routers share updates with each other
  • Routers know the state of all links within their area
  • Routers use different tables to maintain an understanding of the Link-States
    • Neighbor table - list of neighbor routers and the interface
    • Topology table - the Link-State table, map of all links within an area and their status
    • Shortest-Path table - best rotues to each particular destination - this is the routing table
  • Convergence is quick
  • Loops are avoided
  • Because of the three tables needing to be maintained, it could use more RAM and CPU resources
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