IGP and EGP

Question 1

AS (Autonomous System)

Answer 1

• Autonomous
  
  • Existing as an independent entity

• Group of IP routes under common control

• RFC 1930, Section 3: Definitions
• “An AS is a connected group of one or more IP
prefixes run by one or more network operators
which has a SINGLE and CLEARLY DEFINED routing
policy.”

• Important point of reference for discussing Interior
Gateway Protocols and Exterior Gateway Protocols

Question 2

IGP (Interior Gateway Protocol)

Answer 2

• Used within a single autonomous system (AS)
• Not intended to route between AS
• That’s why there’s Exterior Gateway Protocols
(EGPs)

• IPv4 dynamic routing
  
  • OSPFv2 (Open Shortest Path First)
  • RIPv2 (Routing Information Protocol version 2)
  • EIGRP (Enhanced Interior Gateway Routing Protocol)
• IPv6 dynamic routing
  
  • OSPFv3
  • EIGRP for IPv6
  • RIPng (RIP next generation)

Question 3

EGP (Exterior Gateway Protocol)

Answer 3

• Used to route between autonomous systems
  
  • Leverages the IGP at the AS to handle local routing
• BGP (Border Gateway Protocol)
  
  • Many organizations use BGP as their EGP