Network Routing and Communication

Routing Protocols – BGP, RIP, OSPF

Learning Outcome

Google Maps checks different roads and traffic conditions.

Google Maps selects the fastest and safest route.

At every turn, Google Maps guides the traveler.

The traveler safely reaches the destination.

 What are Routing Protocols?

A routing protocol enables routers to determine the most efficient path for forwarding data across a network. When a router receives a packet, it uses these protocols to decide the best route to reach the destination, ensuring data is delivered quickly and reliably. By dynamically managing routes, routing protocols help prevent issues like routing loops, where packets circulate endlessly and cause network congestion and delays.

Static vs Dynamic Routing

There are two ways to configure network routers to forward traffic: static or dynamic routing.

Static Routing

Static routing is a method where routes are manually configured by a network administrator and do not change automatically.

Routes are manually configured by a network administrator

Does not change automatically if the network changesa

Suitable for small, simple networks

Less overhead (no protocol traffic)

No automatic updates

Low CPU and bandwidth usage

Requires manual maintenance

Not scalable

Dynamic Routing
 

Dynamic routing uses routing protocols to automatically learn and update routes based on current network conditions.

Routes are learned automatically using routing protocols

Adjusts automatically when network changes occur

Suitable for large and complex networks

Requires more CPU and bandwidth

Adapts to network failures

Uses algorithms to find best path

More scalable than static routing

Interior Gateway Protocol (IGP) vs Exterior Gateway Protocol (EGP)

There are two types of routing protocols: interior and exterior.

IGPs are routing protocols used to exchange routing information within a single autonomous system (AS).

Used within a single network (Autonomous System.

Faster and optimized for internal routing

Examples:

1. RIP
2. OSPF

Interior Gateway Protocol (IGP) vs Exterior Gateway Protocol (EGP)

There are two types of routing protocols: interior and exterior.

Exterior Gateway Protocols (EGP) instead run on routers that belong to different organizations, or Autonomous Systems.

Used between different networks (Autonomous Systems)

Handles routing on the internet scale

Example: BGP

 Distance Vector vs Link State Protocols

Distance Vector

A routing method where routers share their routing tables with neighbors and choose paths based on distance (hop count).

Routers share routing information only with their immediate neighbors

Each router knows limited information (next hop and distance)

Updates are sent periodically

Slower and can sometimes create routing loops

Link State Protocol

A routing method where routers build a complete map of the network and calculate the best path using algorithms.

Routers share information with all routers in the network

Each router builds a full network map (topology)

Updates are sent only when changes occur

Faster and more accurate

Introduction to BGP

BGP is a dynamic routing protocol used to exchange routing information between different networks on the Internet. It is known as the “backbone of the Internet” because it connects large networks like ISPs.

BGP (Border Gateway Protocol) is a path vector routing protocol used to exchange routing information between different networks on the internet.

It is the main routing protocol of the internet, responsible for deciding how data travels between large networks.

Exterior Gateway Protocol (Internet-level routing)

An Exterior Gateway Protocol (EGP) is a type of routing protocol used to exchange routing information between different networks (Autonomous Systems). It operates at the internet level, connecting large networks like ISPs and enterprise networks.

EGPs help determine how data travels across the global internet, not just within a single network.

Works between networks, not inside one network

Uses Autonomous Systems (AS) to identify networks

Main example: BGP (Border Gateway Protocol)

It connects large entities like:

• ISPs - (Internet Service Providers)
• Data centers
• Enterprise networks

Each network (called an Autonomous System – AS) has its own routing

EGP shares route information between these AS

Routers decide the best path based on:

Policies

Path information

Data travels across multiple networks to reach its destination

How it Works?

Path Vector Concept

The Path Vector Concept is a routing method where the entire path to a destination network is stored and shared and used by BGP where each route includes the complete path (list of Autonomous Systems - AS) that data must travel through.

Instead of using only distance or cost, BGP includes a list of Autonomous Systems (AS) that the data must pass through. This helps routers make better decisions and avoid routing loops.

    A BGP router advertises a route with its AS number

    The route is passed along to other AS

   Routers check the AS path list to:

Choose the best path

Avoid loops

   Routers check the AS path list to:

Choose the best path

Avoid loops

How it Works?

BGP Path vector concept - Step by step

 Autonomous System (AS) in BGP

An Autonomous System (AS) is a group of networks and routers that are managed by a single organization and follow a common routing policy. Each AS is identified by a unique number called an Autonomous System Number (ASN).

In BGP, AS is the basic unit of routing on the Internet.

BGP uses these AS numbers to exchange routing information between different networks.

• One AS = one administrative control (like an ISP or large company)

• Each AS has a unique ASN

• BGP uses AS numbers to track and manage routing paths

• Helps organize the internet into manageable sections

• Allows routing decisions based on policies and rules

• Prevents routing loops using AS path checking

Every AS is identified by a unique AS Number (ASN).

Types:

1. Private ASN: Used inside organizations

2. Public ASN: Used on the Internet (assigned globally)

How BGP Controls Internet Routing

BGP controls internet routing by exchanging network paths between Autonomous Systems (AS) and selecting the best route based on policies and path attributes, not just distance. Unlike other protocols, BGP focuses on policy-based routing, not just the shortest path.

Exchange of Routing Information

• Routers share available network paths along with AS path information

• Each route includes attributes like:

1. AS Path

2. Next Hop

3. Origin

Best Path Selection

• BGP selects the best route based on:
• Shortest AS path

Example:

• Prefer cheaper routes

• Avoid certain networks

• Control incoming/outgoing traffic

Basic Working Idea of BGP

BGP works by connecting different networks (Autonomous Systems) and exchanging routing information to decide the best path for data.

Routers communicate with each other, share available routes, and select the most suitable one based on rules and path attributes.

It ensures data travels efficiently across the internet between multiple networks.

Neighbor Connection (Peering)

• BGP routers first establish a connection with other routers (called peers)

Route Exchange

• Routers share information about the networks they can reach

• This includes the AS path and other attributes

Path Storage

• A router may receive multiple paths to the same destination

• It stores all possible routes

Best Path Selection

• The router selects the best path based on:

  1. AS path length

  2. Policies (rules set by admin)

  3. Other attributes

Route Advertisement

• The selected best route is shared with other routers

• This spreads routing information across networks

Introduction to OSPF

OSPF (Open Shortest Path First) is a dynamic routing protocol used to find the best path in a network. It uses a more advanced method than RIP and is suitable for large and complex networks. OSPF is a link-state routing protocol used to find the most efficient path for data in a network.

It calculates the best path using an algorithm called Shortest Path First (SPF)

Works within a single organization (Interior Gateway Protocol)

   SENDER: Your Phone

5 - SESSION LAYER

• Creates, manages, and ends communication sessions between devices.
• Keeping chat session active.

3 - NETWORK LAYER

• Adds IP addresses and finds the best route to the destination.

• Routers forwarding packets across the internet.

1 - PHYSICAL LAYER

• Converts data into electrical, optical, or radio signals for transmission.

• Network cables, switches, radio waves.

   RECEIVER: Friend’s Phone

5 - SESSION LAYER

• Maintains and manages the communication session.

• Keeping chat sessions active.

3 - NETWORK LAYER

• Reads IP addresses and delivers packets to the correct device.

• Identifying destination IP address.

1 - PHYSICAL LAYER

• Receives raw signals and converts them back into bits (0s and 1s).

• Receiving signals through cables or Wi-Fi.

Advantages of OSI Model

Simplifies complex network communication

Helps in troubleshooting (identify the layer of Issue easily)

Allows different vendors and technologies to work together.

Each layer can be developed, tested, and updated independently.

Good learning model for students and beginners.

Summary

Which layer would you investigate if there is NO network signal at all?

Which layer would you investigate if there is NO network signal at all?