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Internet Routing and Routing Protocols

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Helsinki Central Railway Station, Helsinki, Finland - Hsi-Pin Ma)
 


- Overview

Internet routing and routing protocols are fundamental to how data travels across the internet. Routing protocols dictate how routers communicate to determine the best path for data packets to reach their destination. 

These protocols enable routers to share information about network topology, allowing them to dynamically adjust to changing network conditions and ensure reliable data delivery. 

Key concepts: 

1. What is Routing?

  • Routing is the process of selecting a path for data packets to travel across networks.
  • On the internet, routers make routing decisions based on routing protocols.
  • Routing protocols help routers find the most efficient path for data to travel from source to destination.


2. What are Routing Protocols? 

  • Routing protocols are sets of rules and algorithms that routers use to exchange information about network topology and make routing decisions.
  • They enable routers to discover optimal paths for data transmission and adapt to network changes.
  • Examples include RIP, OSPF, EIGRP, and BGP.


3. Types of Routing Protocols: 

  • Distance Vector: These protocols share routing information with neighboring routers, relying on hop count or other metrics to determine the best path. RIP is a common example.
  • Link State: These protocols flood the network with information about network topology, allowing routers to build a complete map of the network and calculate the shortest path using algorithms like Dijkstra. OSPF and IS-IS are examples.
  • Path Vector: These protocols advertise paths to networks, allowing routers to make routing decisions based on path attributes. BGP is the primary example used for routing between different autonomous systems (ASs) on the internet.


4. Key Functions of Routing Protocols: 

  • Learning Routes: Routers use routing protocols to discover and learn about available paths to different networks.
  • Building Routing Tables: Routing protocols populate routing tables on routers, which contain information about the best paths to reach various destinations.
  • Dynamic Adaptation: Routing protocols enable routers to adapt to network changes, such as link failures or congestion, by recalculating routes and updating routing tables.


5. Importance of Routing Protocols: 

  • Fault Tolerance: Routing protocols enable the internet to be fault-tolerant by providing alternative paths when a link or router fails.
  • Efficiency: By choosing the most efficient paths, routing protocols minimize latency and ensure fast data delivery.
  • Scalability: Routing protocols allow networks to scale to accommodate increasing traffic and complexity.


6. Interior vs. Exterior Routing Protocols: 

  • Interior Gateway Protocols (IGPs): These protocols operate within a single autonomous system (AS), which is a network under the control of a single organization. Examples include OSPF, RIP, and EIGRP.
  • Exterior Gateway Protocols (EGPs): These protocols operate between different autonomous systems, such as on the internet. BGP is the primary example.

 

- Routers, Routing Protocols, and Routing Algorithms

A routing protocol specifies how routers communicate with each other, disseminating information that enables them to select routes between any two nodes on a computer network. 

The purpose of routing protocols is to learn of available routes that exist on the enterprise network, build routing tables and make routing decisions. Some of the most common routing protocols include RIP, IGRP, EIGRP, OSPF, IS-IS and BGP.

Routing algorithms determine the specific choice of route. Each router has a priori knowledge only of networks attached to it directly. 

A routing protocol shares this information first among immediate neighbors, and then throughout the network. This way, routers gain knowledge of the topology of the network.

 

- 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

Although there are many types of routing protocols, three major classes are in widespread use on IP networks:

 

- Major Internet Routing Protocols

Internet routing protocols are algorithms that determine how packets of data travel from source to destination. Some 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 Router (Internet Backbone Router) 

A core router is a router designed to operate in the Internet backbone, or core. The core router that resides within the middle of the network rather than at its periphery. The routers that make up the backbone of the Internet are core routers. 

To fulfill this role, a core router must be able to support multiple telecommunications interfaces of the highest speed in use in the core Internet and must be able to forward IP packets at full speed on all of them. It must also support the routing protocols being used in the core. A core router is distinct from an edge router.

 

- Edge Router

Edge routers sit at the edge of a backbone network and connect to core routers. Edge routers are gateways that accept inbound traffic into your network. Edge routers work to secure the network edge and protect the core by characterizing and securing IP traffic from other edge routers as well as core routers. They differ from core routers in that core routers forward packets between routers to manage traffic and prevent packet loss, often using multiplexing. 

Edge routers also referred to as access or branch routers, are specialized routers that act as gateways at the network edge. They enable connectivity between an enterprise network and an external network. They are typically used at the wide area network (WAN) or the Internet.

An edge router should support edge interconnect protocols: IPv4, IPv6, ISO, MPLS. It should also support routing protocols: Static routes, OSPF, OSPF-TE, OSPFv3, IS-IS, BGP.

 

 

[More to come ...]

  

 


 
 
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