1. Types of Routing Protocols
Routing protocols are mainly categorized into Static and Dynamic routing.
A. Static Routing
- Definition: The routes are manually configured by a network administrator.
- Advantages:No overhead in CPU/memory.More secure since no updates are exchanged.Works well in small networks.
- Disadvantages:Difficult to manage in large networks.Does not automatically adapt to network changes.
B. Dynamic Routing
Dynamic routing automatically adjusts to network topology changes using routing algorithms. It is further divided into IGP (Interior Gateway Protocol) and EGP (Exterior Gateway Protocol).
2. Interior Gateway Protocols (IGP)
Used for routing within an Autonomous System (AS).
a) Distance Vector Routing Protocols
- Definition: Routers share information with their directly connected neighbors.
- Key characteristics:Uses hop count as the primary metric.Periodic updates (which can lead to slow convergence).Prone to routing loops (fixed using split horizon, route poisoning).
- Examples:RIP (Routing Information Protocol):Maximum hop count = 15 (16 is considered unreachable).Updates every 30 seconds.Uses Bellman-Ford Algorithm.IGRP (Interior Gateway Routing Protocol):Cisco proprietary (deprecated in favor of EIGRP).Uses a composite metric (Bandwidth, Delay, Load, Reliability).
b) Link-State Routing Protocols
- Definition: Instead of sending complete routing tables, routers exchange topology information to build a complete network map.
- Key characteristics:Uses Dijkstra’s Shortest Path First (SPF) Algorithm.Faster convergence than Distance Vector protocols.Less prone to routing loops.
- Examples:OSPF (Open Shortest Path First):Open standard protocol (not vendor-specific).Uses Areas to divide large networks (Area 0 as Backbone).Uses Cost (based on bandwidth) as the metric.ISIS (Intermediate System to Intermediate System):Commonly used in large ISPs.Uses CLNS (Connectionless Network Service) instead of IP initially.Scalable for very large networks.
c) Hybrid Routing Protocol
- Definition: Combines features of both Distance Vector and Link-State.
- Example:EIGRP (Enhanced Interior Gateway Routing Protocol):Cisco proprietary.Uses DUAL (Diffusing Update Algorithm) for fast convergence.Uses a composite metric (Bandwidth, Delay, Load, Reliability).Supports VLSM (Variable Length Subnet Masking).
3. Exterior Gateway Protocol (EGP)
Used for routing between different Autonomous Systems (AS).
a) Path Vector Routing Protocol
- Definition: Maintains the path of each route (instead of just hop count or link-state information).
- Example:BGP (Border Gateway Protocol):The backbone of the Internet.Uses Path Attributes (AS Path, Next-Hop, Local Preference, MED, etc.).Supports policies for route selection.Works on TCP Port 179.
- Two types of BGP:iBGP (Internal BGP) – Used within an AS.eBGP (External BGP) – Used between different AS.
