EGP vs. IGP

Attribute	EGP	IGP
Definition	Exterior Gateway Protocol	Interior Gateway Protocol
Scope	Operates between autonomous systems (AS)	Operates within a single AS
Routing Protocol	Distance Vector or Path Vector	Distance Vector, Link-State, or Hybrid
Routing Table	Contains routes to other AS	Contains routes within the same AS
Metrics	Usually based on hop count or AS path length	Varies based on the specific IGP used
Administrative Distance	Usually higher than IGP	Usually lower than EGP
Examples	BGP (Border Gateway Protocol)	OSPF (Open Shortest Path First), RIP (Routing Information Protocol)

Introduction

Exterior Gateway Protocol (EGP) and Interior Gateway Protocol (IGP) are two fundamental routing protocols used in computer networks. While both protocols serve the purpose of exchanging routing information, they differ in various aspects. In this article, we will explore and compare the attributes of EGP and IGP, shedding light on their functionalities, scope, scalability, and routing algorithms.

Functionality

EGP, as the name suggests, is primarily designed for exchanging routing information between autonomous systems (AS) in the Internet. It enables the communication between different ASs, allowing them to share information about the best paths to reach specific destinations. On the other hand, IGP is used within an AS to facilitate routing between routers within the same network. It focuses on the internal routing of packets within a single organization or network.

Scope

EGP operates at the network layer (Layer 3) of the OSI model and is responsible for exchanging routing information between different ASs. It is used to connect multiple networks and ensure efficient routing across the Internet. In contrast, IGP operates at the interior gateway level within an AS, providing routing information to routers within the same network. It is responsible for determining the best paths for packets to travel within the organization's network.

Scalability

When it comes to scalability, EGP has limitations due to its design. As EGP is an inter-domain routing protocol, it requires each AS to maintain a full routing table, which can become unmanageable as the number of ASs in the Internet grows. On the other hand, IGP is more scalable as it operates within a single AS. It allows for hierarchical routing, where routers are organized into areas or domains, reducing the size of routing tables and improving overall scalability.

Routing Algorithms

EGP uses a path vector routing algorithm, which takes into account various factors such as the number of AS hops, AS path length, and policies to determine the best path for routing packets between ASs. This algorithm ensures that packets are routed efficiently across different ASs while considering the policies set by each AS. In contrast, IGP employs various routing algorithms, such as OSPF (Open Shortest Path First) and RIP (Routing Information Protocol), to determine the best paths within an AS. These algorithms consider factors like link costs, network congestion, and network topology to make routing decisions.

Convergence Time

Convergence time refers to the time it takes for the network to reach a stable state after a change in the network topology or a link failure. EGP generally has a longer convergence time compared to IGP. This is because EGP relies on the exchange of routing information between ASs, which can introduce delays and increase the time required for the network to converge. IGP, operating within a single AS, can achieve faster convergence as it only needs to update routing information within the organization's network.

Security

Security is a crucial aspect of any routing protocol. EGP provides better security features compared to IGP. EGP supports authentication mechanisms, such as MD5 authentication, to ensure the integrity and authenticity of routing information exchanged between ASs. This helps prevent unauthorized entities from injecting false routing information into the network. On the other hand, IGP protocols like OSPF and RIP have limited built-in security mechanisms, making them more vulnerable to attacks like route poisoning or spoofing. Additional security measures, such as IPsec or Virtual Private Networks (VPNs), are often required to secure IGP-based networks.

Conclusion

In summary, EGP and IGP are two distinct routing protocols with different functionalities, scopes, scalability, routing algorithms, convergence times, and security features. EGP is designed for inter-domain routing, facilitating communication between different ASs in the Internet, while IGP focuses on intra-domain routing within a single AS. While EGP provides better security features, IGP offers improved scalability and faster convergence times. Understanding the attributes of these protocols is essential for network administrators and engineers to make informed decisions when designing and managing complex networks.