11. Route

Router

• connect multiple networks

• determine the best path to send packets

  • longest match

  • the path with the lowest metric

    • hop count

    • cost

    • bandwidth, delay, load, reliability

  • administrative distance (AD)

    • the lower, the more trustworthy

• forward packets toward their destination (routing table)

  • process switching

  • fast switching

  • express forwarding

• forwarding decision

  • Forwards the Packet to a Device on a Directly Connected Network

  • Forwards the Packet to a Next-Hop Router

  • Forwards the Packet to default route

  • Drops the Packet - No Match in Routing Table

Routing Table

• Directly connected routes

  • Local Route interfaces

• Remote routes

• Default route

• Each Route Entry

  • Route source

  • Destination network

  • Administrative distance

  • Metric

  • Next-hop

  • Outgoing interface

  • timestamp

Routing Protocol

• Static

  • manually configured

    • Stub networks

      • ip route dest-network subnet-mask next-hop

      • ip route dest-network subnet-mask exit-interface

      • ipv6 route dest-network/prefix-length next-hop

      • ipv6 route dest-network/prefix-length exit-interface

    • summarizing route

    • backup route

      • higher administrative distance than primary route

    • default route

      • ip route 0.0.0.0 0.0.0.0 next-hop

      • ip route 0.0.0.0 0.0.0.0 exit-interface

      • ipv6 route ::/0 next-hop

      • ipv6 route ::/0 exit-interface

• Dynamic

  • automatically updated routing table

    • network discovery

    • maintaining routing tables

  • components

    • Data structures

    • Routing protocol messages

    • Algo

  • classification

    • Purpose

      • Interior Gateway Protocol (IGP)

        • RIP, OSPF, eIGRP

      • Exterior Gateway Protocol (EGP)

        • BGP

    • Operation

      • distance vector

        • RIPv1, RIPv2, EIGRP

      • link-state

    • OSPF

    • behavior

      • classful

      • classless