Why dynamic routing is preferred over static routing algorithm in a network which changes continuously?

In the Static routing, the table is set up and modified manually whereas in the Dynamic routing the table is built automatically with the help of the routing protocols. Dynamic routing is preferred over static routing because of the major issue in static routing where in case of link/node failure the system cannot recover. The dynamic routing overcomes from the static routing limitations.

Routing is the process of transferring the packets from one network to another network and delivering the packets to the hosts. The traffic is routed to all the networks in the internetwork by the routers. In the routing process a router must know following things:

• Destination device address.
• Neighbor routers for learning about remote networks.
• Possible routes to all remote networks.
• The best route with the shortest path to each remote network.
• How the routing information can be verified and maintained.

Content: Static and Dynamic Routing

Comparison Chart

Definition of Static Routing

Static routing does not involve any change in routing table unless the network administrator changes or modify them manually. Static routing algorithms function well where the network traffic is predictable. This is simple to design and easy to implement. There is no requirement of complex routing protocols.

The routing decisions are not made by current topology or traffic because the static routing systems can not react to network changes hence it doesn’t require extra resources to learn the changes. That is the reason, static routing is considered as inappropriate for large and constantly changing networks.

Static routing is also known as non-adaptive routing which enables a pre-computed route to be fed into the routers offline. The administrative distance is a metric to measure the trustworthiness of the information received from a router. The default administrative distance for static route is 1, consequently the static routes will only be covered in the routing table when there is a direct connection to that network. Static routes can be considered as an efficient method for a small and simple network that does not change frequently.

Definition of Dynamic Routing

Dynamic routing is a superior routing technique which alters the routing information according to the altering network circumstances by examining the arriving routing update messages. When the network change occurs, it sends out a message to the router to specify that change, then the routes are recalculated and sent as a new routing update message. These messages pervade the network, enabling the router to change their routing tables correspondingly.

The technique uses routing protocols to disseminate knowledge such as RIP, OSPF, BGP, etc. Unlike static routing, it does not require manual updation instead its automatic in manner and updates the routing table information periodically relying upon network conditions. For doing so, it requires extra resources for storing the information.

Dynamic routing or otherwise called as adaptive routing. The routing decisions are altered in these algorithms to mirror the changes in the topology or traffic. There are various adaptive algorithms which can be classified according to the source of information (from where router get the information, adjacent routers or from all routers), change in routes (whether the route is changing when load changes or when topology changes), optimization metrics used (distance, number of hops, residual bandwidth).

The routes on which dynamic routing is performed are known as dynamic routes where the information is responsive to changes in the network so that it is consistently being updated. Though, there is always a slack between the period that a network changes and when all the routers are informed about the change. The router tries to match the network change, and it causes a delay which is also known as convergence time. The convergence time must be shorter. The larger network requires dynamic routing because with static routing larger networks could not be manageable and result in loss of connectivity.

Key Differences Between Static and Dynamic Routing

1. The routers are configured manually, and the table is also created manually in static routing whereas in dynamic routing the configuration and table creation is automatic and router driven.
2. In static routing, the routes are user-defined while in dynamic routing the routes are updated as topology changes.
3. Static routing does not employ complex algorithms. As against, dynamic routing uses the complex algorithm for calculating shortest path or route.
4. Dynamic routing is suitable for large networks where the number of hosts is high. Conversely, static routing can be implemented in a small network.
5. When a link fails in static routing, the rerouting is discontinued and requires manual intervention to route traffic. In contrast, link failure in dynamic routing does not disrupt rerouting.
6. The message broadcast and multicast in dynamic routing makes it less secure. On the other hand, static routing does not involve advertisement which makes it more secure.
7. Dynamic routing involves protocols such as RIP, EIGRP, BGP, etc. Inversely, static routing does not require such protocols.
8. Static routing does not need any additional resources while dynamic routing requires additional resources such as memory, bandwidth, etc.

Advantages and Disadvantages Static Routing

Advantages 

• Easily implemented in a small network.
• No overheads are produced on router CPU.
• Secure because the routes are managed statically.
• It is predictable as the route to the destination is fixed.
• Extra resources (such as CPU and memory) are not required as update mechanisms are not needed.
• Bandwidth usage is not required between routers.

Disadvantages 

• Unsuitable for complex topologies and large networks.
• Large networks increase configuration complexity and time consumption.
• Link failure can hinder traffic rerouting.
• The administrator must be extra careful while configuring the routes.

Advantages and Disadvantages of Dynamic Routing

Advantages

• Suitable for all the topologies.
• Network size doesn’t affect the router operations.
• Topologies are adapted automatically to reroute the traffic.

Disadvantages

• Initially, it could be complicated to implement.
• The broadcasting and multicasting of routing updates make it less secure.
• Routes rely on current topologies.
• Additional resources are required such as CPU, memory and link bandwidth.

Conclusion

Routing is one of most important operation of computer networking in which the data packet is moved from source to destination using an optimized path with a low delay; the path is elected with the help of routing techniques. The difference between static and dynamic routing lies in the table entries updation. In static routing, the routing information is manually updated while in dynamic routing the information is automatically updated using protocols.