BGP Routing

Injecting routes into BGP.

  • Use the network command.
    • Different than the network command in iGP; it isn’t used to listen/active interfaces.
    • the BGP network command looks for the prefix in the routing table and originates that into the BGP table.
    • If no mask is defined, IOS assumes a classful network.
    • Classful route is added if:
      • the exact route is in the ip routing table
      • Any subset of routes are in the routing table (only with auto-summery)
    • create a null0 route
      • ┬áip route null0
router bgp 20
 bgp log-neighbor-changes
 network mask
 neighbor remote-as 10
 neighbor ebgp-multihop 255
 neighbor update-source Loopback1

  • Route redistribution.
    • redistribute iGP into BGP.
    • Internal routes are prefered over external routes.
R2(config)#router bgp 20
R2(config-router)#redistribute ? 
    bgp            Border Gateway Protocol (BGP)
    connected      Connected
    eigrp          Enhanced Interior Gateway Routing Protocol (EIGRP)
    isis           ISO IS-IS
    iso-igrp       IGRP for OSI networks
    lisp           Locator ID Separation Protocol (LISP)
    mobile         Mobile routes
    odr            On Demand stub Routes
    ospf           Open Shortest Path First (OSPF)
    ospfv3         OSPFv3
    rip            Routing Information Protocol (RIP)
    static         Static routes
    vrf            Specify a source VRF
  • Route summarization/aggregation
    • aggregate-address [summary-only]

BGP for outbound routing

  • Single homed ( 1 link per ISP, 1 ISP ).
    • Default route will suffice.
    • BGP probably not necessary.
  • Dual homed ( 2+ links per ISP, 1 ISP ).
    • BGP is useful.
    • Static route can also be used:
      • Load share traffic between both circuits
      • prefer one link over the other
  • Single multihomed ( 1link per ISP, 2+ ISPs ).
    • same concept as dualhomed.
  • Dual multihomed (2+ link per ISP, 2+ ISPs).
    • Using BGP takes full advantage

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