Routing Design Principles (EIGRP, OSPF, BGP)

EIGRP design principles

• EIGRP works for arbitrary topologies for small to medium networks.
• A flat EIGRP network doesn’t really scale beyond 400 routers and will lead to performance issuse
  • How to solve this?
    • Stub areas, summerization, route filtering limits the query scope
• If EIGRP doesn’t have a feasible successor it will query all it’s neighbours.
  • “I don’t have a route anymore, don’t route through me, give me a viable route”.
• BFD to optimize convergence (100ms wtih 1000 routes).
• 2 second hello timer, 6 second hold timer ( recommended )

Multiple EIGRP design principles

• Used to merge two networks ( Acquisitions )
• Different administrative groups in a company
• a way to devide large networks ( and control queries )
• Routes are distributed between AS ( don’t loop! )

OSPF design principles

• Number of neighbouring routers ( no more than 60 ).
• Number of routers in an area ( no more than 50 ).
• Number of areas connected to a router ( no more than 3 ).
  • LSDB has to be maintained for all area’s
• The router acting as the DR ( best router).
• Ammount of data in an area impatcs OPSF performance
  • Summarize
  • Stub / Total stub
• Areas should be designed around geography and functional boundries
• Summarization minimizes route change (flapping) impact
• Large networks only have ARBS in AREA 0
• Contigious splitable adressing

BGP design principles

• BGP as IGP:
  • Advantages: 
    • Vendor interoperability
    • per-hop traffic engineering,
    • unequal-cost loadbalancing / anycast routing
    • simpler troubleshouting (as-path)
    • reduced flooding
    • Trust border controll
  • Disadvantages:
    • Default timers are very slow
    • Not available on low-end routers (layer 3 switches)
    • Not as dynamic
    • Full mesh requirement
• Route Reflector design
• Confederate design

All Routing protocols

All routing protocols must detect, propagate, process and update.