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Routing algorithm types: distance vector vs Link State

There are 3 main kinds of routing protocols. This post details them

Distance vector (e.g., RIP)

    • What is advertised is the path (vector) and its cost (distance, typically just the number of hops), hence, the name of this routing protocol category.
    • periodic flooding of routing tables (every 10 - 90s).
    • Thus, long convergence time and useless overhead in case of stable network
    • Adapted to only small networks. That's why RIP is limited to networks with less than 15 routers.

Link state (e.g., OSPF, IS-IS)

    • What is advertised is the link state (all links and their cost), hence, the name of this routing protocol category.
    • Floods only topology changes (link state advertisements): faster convergence time and less overhead than distance vector protocols. Uses keep-alive messages to keep connection to other routers.
    • All routers recalculate routes when topology changes: requires CPU and memory, need to partition the network into areas to avoid having 100 routers recalculating their routing table for every link state change (imagine the case of a flapping link...).

Path vector (e.g., BGP)

    • What is advertised is the path (vector), without distance. The decisions are made based on other elements (typically predefined policies) than a path cost.
The routing complexity of setting up VPNs accross the Internet

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