Interior Border Gateway Protocol (iBGP)

BGP Peering

• The blue routers are iBGP neighbors

iBGP Requirements

• Same AS (Autonomous system) number
• Full Mesh
  • 20 routers on our environment
  • If we wanted to add 1 more router, I have to update every single router and say, hey you got a lot of neighbor
• Explicitly define neighbors
• Must know how to reach neighbors
• Doesn't propagate local updates to local peers
  • If I receive an update and I am local I assume that the other routers also received the update.

iBGP Workarounds

• Loopback Interfaces
  • Software
• Interior Gateway Protocol (IGP)
  • We can advertise it through EIGRP
• Route reflectors
  • Breaks the rule.
  • Typically we assume that everything is full mesh, so they will never tell other routers what they hear from others
  • A Route Reflector we do not have to be full mesh
    • I am C (RR), whatever comes in from A I can propagate it to B.
    • Wait, that is a single point of failure, a terrible idea
      • Yes so you should use two Route Reflectors.

Router BGP Configuration

Router# configuration
router(config)# router bgp 64512
router(config-router)# neighbor 10.1.1.1 remote-as 64512
router(config-router)# network 192.168.254.0

• BGP will look at its local routing table and make sure that it knows how to get to that network before it goes out and it tells the whole world (kind of like a sanity check)

BGP Network Statement

• IGP vs. EGP
• Network is a precise announcement
• Router will verify network in routing table first
  • Hey BGP tell the world that this network is here!