Internet Routing and Routing Protocols

- Types of Routing

Routing is a process which is performed by layer 3 (or network layer) devices in order to deliver the packet by choosing an optimal path from one network to another. 

There are 3 types of routing:

• Static routing – Static routing is a process in which we have to manually add routes in routing table.
• Default Routing – This is the method where the router is configured to send all packets towards a single router (next hop). It doesn’t matter to which network the packet belongs, it is forwarded out to router which is configured for default routing. It is generally used with stub routers. A stub router is a router which has only one route to reach all other networks.
• Dynamic Routing – Dynamic routing makes automatic adjustment of the routes according to the current state of the route in the routing table. Dynamic routing uses protocols to discover network destinations and the routes to reach it. RIP and OSPF are the best examples of dynamic routing protocol. Automatic adjustment will be made to reach the network destination if one route goes down. A dynamic protocol have following features: The routers should have the same dynamic protocol running in order to exchange routes. When a router finds a change in the topology then router advertises it to all other routers.

- Major Classes of Internet Routing Protocols

The three major classes of internet routing protocols are: link-state (IGP type 1), distance-vector (IGP type 2), and exterior gateway protocols. 

Link-state and distance-vector protocols are used within autonomous systems (internal routing), while exterior gateway protocols are used between autonomous systems (external routing). 

1. Link-State Routing Protocols:

• These protocols, like OSPF and IS-IS, flood the network with link-state advertisements (LSAs), allowing each router to build a complete map of the network topology.
• Routers then independently calculate the best paths to destinations based on this map.
• They are generally more scalable and efficient than distance-vector protocols.

2. Distance-Vector Routing Protocols:

• These protocols, like RIP, RIPv2, and IGRP, share routing tables with their neighbors, updating each other on the best routes based on hop count or other metrics.
• They are simpler to implement but can suffer from slow convergence (the time it takes to reach a stable state after a topology change) and potential routing loops.

3. Exterior Gateway Protocols:

• These protocols, like BGP, are used to exchange routing information between different autonomous systems.
• BGP is the dominant protocol for routing on the internet and is used to determine the best paths for traffic to flow between different networks (autonomous systems).

- Major Internet Routing Protocols

Internet routing protocols are algorithms that determine how packets of data travel from source to destination. S

ome common routing protocols include:

• Routing Information Protocol (RIP): RIP is one of the oldest distance vector routing protocols that uses hop count as a routing metric. RIP limits the number of hops allowed in the path from source to destination to prevent routing loops.
• Border Gateway Protocol (BGP): A high-level protocol that determines routing based on other factors such as weight and local preferences. Network administrators can bypass automatic routing decisions made by protocols.
• Open Shortest Path First (OSPF): The link-state IGP uses the Shortest Path First (SPF) algorithm to calculate the shortest path spanning tree.
• Enhanced Interior Gateway Routing Protocol (EIGRP): Popular choice for routing within campus networks. Many network engineers consider EIGRP to be the best choice of routing protocol for private networks.
• Interior Gateway Protocol (IGP): IGP was established to overcome the shortcomings of RIP and is more suitable for large networks. The IGP automatically updates itself when routing changes occur within a particular network.
• Exterior Gateway Protocol (EGP): From the mid-1980s to the mid-1990s, it was used to connect autonomous systems on the Internet. EGP is replaced by BGP.

- Core Routers (Internet Backbone Routers) 

A core router, also known as an Internet backbone router, is a specialized router designed to handle the high-speed traffic within the core of a network, such as the internet backbone or the core network of a large organization. 

Core routers are distinct from edge routers, which connect to the network periphery. 

In essence, core routers form the backbone of the internet, connecting different networks and handling the massive flow of data within these networks. 

Key characteristics of a core router include: 

• High-speed connectivity: Core routers must support multiple high-speed telecommunication interfaces and be able to forward IP packets at their maximum capacity.
• Routing protocol support: They must be compatible with and support the routing protocols used in the core network.
• Location in the network: Core routers are situated in the middle of the network, not at the edges.
• Distinction from edge routers: Core routers are designed for the high-capacity traffic of the network core, while edge routers connect users or smaller networks to the core network.
• Examples of core router usage: Core routers are typically used by large internet service providers (ISPs), large corporations, and cloud providers.

- Edge Routers

Edge routers act as gateways connecting a private network to an external network like the internet, managing traffic flow and security at the network's edge. 

They are distinct from core routers, which focus on internal network traffic management and forwarding. 

Edge routers support various protocols for connectivity and routing, including IPv4, IPv6, MPLS, and routing protocols like OSPF and BGP. 

Key Differences between Edge and Core Routers: 

• Location: Edge routers are at the edge of a network, connecting to external networks, while core routers are within the network's backbone, forwarding traffic between internal networks.
• Function: Edge routers act as gateways, securing and managing traffic entering and leaving the network, while core routers focus on internal traffic forwarding and preventing packet loss.
• Complexity: Edge routers are often simpler devices, while core routers may be more complex with features like multiplexing.
• Security: Edge routers play a crucial role in network security by inspecting and filtering traffic from external sources.
• Protocols: Edge routers support edge interconnect protocols (IPv4, IPv6, MPLS) and routing protocols (Static, OSPF, BGP), according to a technology resource.

Edge Router Characteristics: 

• Gateway Function: They facilitate connectivity between a private network and external networks like the internet or WANs.
• Security: Edge routers employ security measures to protect the network from external threats.
• Traffic Management: They handle traffic flow, ensuring efficient and secure communication.
• Scalability: Edge routers need to support the size and growth of the network, including various link types like 5G.
• Examples: Edge routers can be found at the internet edge or at the edge of a wide area network.

[More to come ...]