Routing protocols are used by routers to determine the best path to route packets through a network. They facilitate the exchange of routing information between routers, allowing them to build and maintain routing tables dynamically. There are several types of routing protocols, each with its own method of determining the best path for data.

Here’s a breakdown of some common routing protocols:

  1. Interior Gateway Protocols (IGPs) – Used within a single autonomous system (AS). a. RIP (Routing Information Protocol):
    • Distance-vector protocol.
    • Uses hop count as its metric, with a maximum of 15 hops.
    • Version 2 supports VLSM (Variable Length Subnet Masking).
    • Slow convergence and not scalable for large networks.
    b. EIGRP (Enhanced Interior Gateway Routing Protocol):
    • Cisco proprietary.
    • Advanced distance-vector protocol.
    • Uses bandwidth and delay by default to calculate the metric.
    • Supports fast convergence.
    c. OSPF (Open Shortest Path First):
    • Link-state protocol.
    • Uses Dijkstra’s algorithm to calculate the shortest path.
    • Divides the large networks into areas for scalability.
    • Supports VLSM.
    d. IS-IS (Intermediate System to Intermediate System):
    • Link-state protocol similar to OSPF.
    • Used mainly in large networks, such as ISPs.
  2. Exterior Gateway Protocols (EGPs) – Used between different autonomous systems. a. BGP (Border Gateway Protocol):
    • Path vector protocol.
    • Most commonly used for routing between ISPs.
    • Uses a list of AS paths to determine the route.
    • Very scalable and can handle thousands of routes.
  3. Hybrid Protocols:
  • EIGRP is often referred to as a hybrid protocol because it incorporates features of both distance-vector and link-state protocols.

Key Features and Concepts in Routing Protocols:

  • Convergence: The time it takes for the protocol to recognize a network change and update all routers in the network with the new routing information.
  • Metric: A value used by routing protocols to determine the best path to a destination. Different protocols use different metrics, such as hop count, bandwidth, delay, etc.
  • Distance Vector: Protocols that use the distance (metric) and direction (vector) to determine the best path. They periodically send updates to neighbors with their view of the network.
  • Link-State: Protocols that build a complete topology of the network. Routers have a full picture of the network and run algorithms to determine the best path.
  • Scalability: How well the protocol can handle larger networks.
  • Autonomous System (AS): A collection of IP networks and routers under the control of a single organization that presents a common routing policy to the Internet.

In conclusion, the choice of routing protocol often depends on the specific requirements and design considerations of the network, such as its size, convergence requirements, and administrative boundaries.