Route Redistribution Crib Notes

These are my ‘crib notes’ that I’ve made to serve as a last minute refresher. Please forgive the grammer / spelling as I did not develop these notes with publishing in mind.

Route Redistribution

***theory***

  • IGRP – Automatically redistributes with EIGRP under the same AS number
  • RIP – You must specify a seed metric other it takes it as 16 – invalid
    • E.g. Redistributed connected metric 2
    • OSPF – Default seed metric is 20 and type E 2, unless it BGP then the metric is 1
      • E.g. redistributed connected subnets
      • Must use subnets in order to get the subnets
      • Type 2 – fixed cost from ABR to destination (default)
      • Type 1 – Cost from local router
      • Default-Information Originate
        • Always – ASBR will always be Default route
        • Not always – ASBR will be default route only if default route is in routing table
        • EIGRP – When redistributing you must specify the 5 k or use default metric
        • Pitfalls – if you see a route in the table, it may not be able to reply if no 2-way redis
        • No seed metric on default for RIP, IGRP, EIGRP, ISIS is 0 – YOU MUST SPECIFY
        • Best Practice – redistribute connected
        • Sub optimal routing: Change AD, Route Metric and use distribute lists
        • Show IP protocols – best for route redistribution & verify on ASBR

  • Route Map: can be used for Policy Based Routing.  Andy DENY clause does not drop packets. If you want to drop it, match the IP address and set interface to null0
  • Passive Interfaces – Accepts routing updates but do not send them
    • OSPF – This will stop the interface from forming a relationship i.e. no hellos
  • Null0 – appear in routing table after manual route summarisation.
  • Distribute list – ACL used for route filtering
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