Exterior Border Gateway Protocol (eBGP)

eBGP Fundamentals

• Connecting to a different AS (Autonomous System)
• Directly attached (no more than 1 hop)
• Advertising Router is set to next hop
• Next hop must be reachable
• Advertising router perform AS-prepending
  • An AS path set is included in your router.
  • We are performing calculations to find the fastest way to get somewhere inside an AS
• AS path ensure loop-free topology

Directly Attached Peers

• Going from a physical interfcae to another physical interface

• eBGP packets use a TTL of 1

• eBGP multihop feature extend this

• BGP metrics are often set on neighbor basis

• No manual neighbor discovery

  • It is hard-coded

• Authentication supported

eBGP Multihop

• TTL > 1

AS Path Prepending

BGP Looking Glass

• Visit www.bgp4.as
• Type 1 Looking glass = Web Interface
• Type 2 looking glass = CLI Interface

• Run: show ip bgp summary