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CCNA Recap: Border Gateway Protocol (BGP)


Singled Homed Exterior Border Gateway Protocol

  • show ip bgp summary
  • show ip bgp
  • show ip bgp neighbors



BGP
  • distance vector
    • advertises all or a portion of its route table to its neighbors.
    • Route exchange
      • internal
        • discovers connectivity among a set of IP subnets
          • RIP
          • IGRP
          • OSPF
          • EIGRP
      • external
      • Route updates contain AS path, network, attributes
        • network statement advertises network dynamically, statically, or through redistribution.
        • attributes inluence best path selection.
        • Autonomous systems define boundaries.
          • They’re a collection of routers under common administrative control w/ a common policy displayed to the world. Tells other routers in other ASes what is has with advertising. Listens to reachability.
  • VLSM support
  • Classless
  • Summarizes any BGP router
    • improves scalability
  • Various metrics
  • No hierarchy
    • traffic between diff. BGP ASes can take different paths.
  • Autonomous building blocks
  • TCP port 179
  • Neighbors are specifically configured
    • Only exchanges routes with neighbors
    • Neighbors can be in the same AS (internal BGP) or not (external BGP)
      • You have to make sure they know they’re neighbors internally.
  • synch. database for initial update
    • incremental updates
  • 60 sec. Hello
  • 180 Hold

  • Route reflectors
  • Unicast traffic

Customer network ————— [          you           ] ———— ISP
  you need
* AS numbers
yours, remotes, must be different
* neighbors involved
* networks that should be advertised.
1, Define BGP
config t
router bgp [AS #, 1  - 65535]

2, establish neighbor relationships
neighbor x.x.x.x remote-as [AS #]

3, advertise
network x.x.x.x mask c.c.c.c



EMPLOYERS: This is me putting new skills into practice.

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