Static and Dynamic Routing

Routing
  • Send IP packets across the network
    • Forwarding decisions are based on destination IP address
  • Each router only knows the next step
    • The packet asks for directions every hop along the way
    • The list of directions is held in a routing table
Routing
  • Different topologies use different data link protocols
    • Ethernet, HDLC, etc.
  • Each router rewrites the frame to add its own data-link header
    • The IP packet remains intact
Static routing
  • Administratively define the routes - You're in control
  • Advantages
    • Easy to configure and manage on smaller networks
    • No overhead from routing protocols (CPU, memory, bandwidth)
    • Easy to configure on sub networks (only one way out)
    • More secure - no routing protocols to analyze
  • Disadvantages
    • Difficult to administer on larger networks
    • No automatic method to prevent routing loops
    • If there's a network change, you have to manually update the routes
    • No automatic rerouting if an outage occurs
Dynamic routing
  • Routers send routes to other routers
    • Routing tables are updated in (almost) real-time
  • Advantages
    • No manual route calculations or management
    • New routes are populated automatically
    • Very scalable
  • Disadvantages
    • Some router overhead required
    • Requires some initial configuration to work properly
Default route
  • A route when no other route matches
    • The "gateway of last resort"
  • A remote site may have only one route
    • Go that way -> rest of the world
  • Can dramatically simplify the routing process
    • Works in conjunction with all other routing methods

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