1. What Are Routing Protocols?

Routing protocols are rules and algorithms used by routers to:

• Discover available networks.

• Exchange routing information with other routers.

• Build and maintain routing tables.

• Select the best path for data packets.

Routing protocols work at Layer 3 (Network Layer) of the OSI model.

2. Types of Routing Protocols

3. Routing Protocols Overview

A. RIP (Routing Information Protocol)

Overview

• Type: IGP, Distance Vector

• Metric: Hop count (max 15 hops)

• Algorithm: Bellman-Ford

• Versions: RIP v1, RIP v2

• Best for: Small networks

How RIP Works

• Routers send routing updates every 30 seconds.

• Uses hop count to choose the shortest path.

• If more than 15 hops, the network is unreachable.

Example Command (Cisco)

Router(config)# router rip
Router(config-router)# network 192.168.1.0
Router(config-router)# network 192.168.2.0

Advantages

• Simple to configure.

• Works well for small networks.

Disadvantages

• Slow convergence.

• Limited scalability.

• Uses more bandwidth due to frequent updates.

B. OSPF (Open Shortest Path First)

Overview

• Type: IGP, Link State

• Metric: Cost (based on bandwidth)

• Algorithm: Dijkstra’s Shortest Path First (SPF)

• Best for: Medium to large enterprise networks

How OSPF Works

• Divides a network into areas for efficiency.

• Uses a link-state database to calculate the best path.

• Sends updates only when topology changes, not periodically.

Example Command (Cisco)

Router(config)# router ospf 1
Router(config-router)# network 192.168.1.0 0.0.0.255 area 0
Router(config-router)# network 192.168.2.0 0.0.0.255 area 0

Advantages

• Fast convergence.

• Scalable for large networks.

• Supports VLSM and CIDR.

Disadvantages

• More complex configuration.

• Consumes more memory and CPU.

C. BGP (Border Gateway Protocol)

Overview

• Type: EGP, Path Vector

• Metric: AS-Path, policy-based

• Best for: Internet routing between Autonomous Systems (AS)

How BGP Works

• BGP connects different organizations or ISPs.

• Chooses the best path based on multiple attributes like:

  • AS-path length

  • Local preference

  • MED (Multi-Exit Discriminator)

• Ensures global routing stability.

Example Command (Cisco)

Router(config)# router bgp 65001
Router(config-router)# neighbor 192.168.1.2 remote-as 65002
Router(config-router)# network 203.0.113.0 mask 255.255.255.0

Advantages

• Highly scalable.

• Can handle thousands of routes.

• Used on the Internet backbone.

Disadvantages

• Complex configuration.

• Slower convergence than OSPF or EIGRP.

D. EIGRP (Enhanced Interior Gateway Routing Protocol)

Overview

• Type: IGP, Hybrid (Distance Vector + Link State)

• Metric: Composite (Bandwidth, Delay, Reliability, Load)

• Algorithm: DUAL (Diffusing Update Algorithm)

• Best for: Medium to large Cisco-based networks

How EIGRP Works

• Uses DUAL algorithm to ensure loop-free and fast convergence.

• Supports VLSM and CIDR.

• Sends partial updates instead of entire routing tables.

Example Command (Cisco)

Router(config)# router eigrp 100
Router(config-router)# network 192.168.1.0
Router(config-router)# network 192.168.2.0

Advantages

• Faster convergence than RIP and OSPF.

• Uses multiple metrics for better path selection.

• Less bandwidth usage due to partial updates.

Disadvantages

• Cisco proprietary (not fully supported on all devices).

• More complex than RIP.

4. Comparison of RIP, OSPF, BGP, and EIGRP

5. Diagram: Routing Protocols

      [LAN A] -------- Router 1 --- OSPF --- Router 2 -------- [LAN B]
                            \                       /
                             \---- EIGRP ---------/
                              \
                               \------ BGP ------- Internet Backbone

• RIP → For very small LANs.

• OSPF → Inside organizations.

• EIGRP → Cisco-heavy networks.

• BGP → Internet-wide routing.

6. Summary

• RIP → Simple, but limited (15 hops max).

• OSPF → Best for large enterprise networks.

• BGP → Backbone of the Internet.

• EIGRP → Fast, efficient, and Cisco-optimized.