Dynamic Routing Protocols

Routing protocols is based on where they are used between two solutions:

  1. Interior Gateway Protocols  (IGP)
  2. Exterior Gateway Protocols (EGP)
Interior Gateway Protocols :
  • Open Shortest Path First (OSPF),
  • Enhanced Interior Gateway Protocol (EIGRP, Cisco proprietary protocol),
  • Intermediate System to Intermediate System (IS-IS).
  • Routing Information Protocol (RIP),
Exterior Gateway Protocols
  • Border Gateway Protocol  (BGP)

IGPs are designed to work in private networks.
EGPs are used to provide paths in the public network (Internet).

We can also classify routing protocols based on the algorithm they use to distribute and maintain information (routing table). There are three major algorithms supported by Cisco routers:
  1. Distance Vector (DV, aka Bellman-Ford) RIP , EIGRP ( using DUAL  Diffusing Update ALgorithm )
    Routers do not know the topology of the network
    Routers advertise their full routing table periodically
    Routers perform automatic summarization
    No VLSM support
    Routers are slow to converge
    Routers use simple metric
    The Distance Vector algorithm uses techniques to prevent rooting loops and infinity count :

    • Triggered Update (aka flash update)
    • Route Poisoning
    • Maximum Metric (RIP considers max 15 hops ,16 hops as inaccessible)
    • Poison Reverse
    • Hold-Down Timer
    • Split-Horizon
  1. Link-StateOSPF ( Dijkstra’s algorithm ), IS-IS.
  2. Path Vector  BGP

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