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Routing Protocols & Routing Daemons: RIP, OSPF, and BGP

Study material and explanations for Unit 5

Routing Protocols, Gateway Information, and Routing Daemons: RIP, OSPF, and BGP

The global Internet is not one single giant network. It is a network of networks—divided into thousands of independent administrative domains called Autonomous Systems (AS) (e.g., Reliance Jio AS, Airtel AS, Google AS).

1. Interior vs. Exterior Gateway Protocols

Classification of Gateway Protocols
🏢 Interior Gateway Protocols (IGP)
  • Used for routing packets INSIDE a single Autonomous System (inside a university or company).
  • Focuses on speed and shortest path metrics.
  • Examples: RIP (Routing Information Protocol), OSPF (Open Shortest Path First).
🌍 Exterior Gateway Protocols (EGP)
  • Used for routing packets BETWEEN different Autonomous Systems across the global Internet.
  • Focuses on business agreements, country policies, and security rules.
  • The Standard: BGP (Border Gateway Protocol).

2. The 3 Major Internet Routing Protocols

1. RIP (Routing Information Protocol)

  • Type: Distance Vector IGP.
  • Metric: Simple Hop Count (number of routers along the path).
  • Hop Limit: Maximum 15 hops (16 = unreachable infinity). Unsuitable for large networks.
  • Update Frequency: Broadcasts full routing table every 30 seconds over UDP port 520.

2. OSPF (Open Shortest Path First)

  • Type: Link State IGP.
  • Metric: Cost based on link bandwidth (10^8 / Bandwidth in bps).
  • Key Features: Divides large networks into hierarchical Areas (with Area 0 as the Backbone Area). Fast convergence with zero routing loops.

3. BGP (Border Gateway Protocol - BGP-4)

  • Type: Path Vector EGP.
  • The Glue of the Internet: Connects major telecom giants (Jio, AT&T, Vodafone) together.
  • Instead of hop count, BGP stores the complete list of Autonomous System numbers (AS-Path) that a packet must traverse to reach a destination network.

3. What are Routing Daemons? (routed and gated)

In Unix, Linux, and FreeBSD server operating systems, routing protocols are managed by background service programs called Daemons:

  1. routed (Routing Daemon):
    • The original Unix network daemon that implements the RIP protocol.
    • Listens on UDP port 520, collects route broadcasts, and updates the kernel routing table.
  2. gated (Gateway Routing Daemon):
    • A modern, unified routing daemon that replaced routed.
    • Supports multiple routing protocols simultaneously: RIP, OSPF, and BGP all inside one single configurable program.

💡 DAVV Exam Tip

Question (10 Marks): “Explain the difference between Interior and Exterior Gateway Protocols. Compare RIP and OSPF. What is a routing daemon?”

  • Contrast IGP (inside AS) vs EGP (between AS).
  • Compare RIP (Hop count, max 15 hops) vs OSPF (Cost/Bandwidth, unlimited hops, areas).
  • Explain routed (RIP only) vs gated (Multi-protocol: RIP + OSPF + BGP).