What are dynamic routing protocols

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Routing is a procedure of making decisions in which the router (which is a hardware device used in networking to receive and send data in the form of packets on a network) selects the best path to make data transfer from source to destination. A router exists in the network layer in the OSI as well as TCP/IP model. Some functions of a router are:

1. Building an optimal path on a network to reach its destination (in which static and dynamic routing take place).
2. Taking routing decisions.
3. Balancing load.

Types of Routing:

1. Static routing
2. Default routing
3. Dynamic routing

Static and Default routing has some drawbacks, due to which Dynamic Routing was introduced.

• It is a burdensome task to sum up or add-on each route manually to the routing map in a large network.
• Managing its ordering is time-consuming.
• It cannot reroute traffic in case some link fails.

• If the network is complex then it is more difficult to set up.

To overcome the shortcomings of static and default routing, Back in the 1980s, the first-ever Dynamic routing was used in a computer and the protocol which was used in it was the RIP(routing information protocol). 

Dynamic Routing

Dynamic routing is known as a technique of finding the best path for the data to travel over a network in this process a router can transmit data through various different routes and reach its destination on the basis of conditions at that time of communication circuits.

Dynamic Routing

Dynamic routers are smart enough to take the best path for data based on the condition of the present scenario at that time of the network. In case one section fails in the network to transfer data forward dynamic router will use its algorithm (in which they use routing protocols to gather and share information of the current path among them) and it will re-route the previous network over another network in real-time. And this amazing capability and functionality to change paths in real-time over the network by sharing status among them is the key functionality of Dynamic Routing. OSPF (open shortest path first) and RIP are some protocols used for dynamic routing.

In the image above the upper image depicts the path R1->R2->R5->R9->R10 to take data from R1 (source) to R10 (destination) but, then due to some reason R9 fails to process its work then it dynamically builds a new path which is R1->R2->R5->R8->R10.

Unlike the static routers in which the admin was there to reconfigure the change in the router, here it itself changes the route and finds the best network/path.

Working of Dynamic Routing

Working of Dynamic Routing

First, A routing protocol (a protocol that states how the information is going to share between routers and how are they going to communicate with each other to share/distribute information between nodes on a network) must be installed in each router in the network to share information among each other. 
Second, it is started manually to go to the first routing table of the router with router information, and then after that it goes on automatically with the help of a dynamic routing algorithm and dynamically forms the routing table for the rest of the routers in the network. 
Third, then the routing information is exchanged among the routers so in case if the network goes down or the router fails to work and share information with its connected routers then the routing table of each router is modified correctly to that present condition so that it never fails to deliver information to the destination. 
Fourth, hosts are present to check or match the default gateway address to the IP addresses of the local router.

Purpose 

Dynamic protocols were introduced to:

1. Explore every single path and choose the best path.
2. Sharing of information about the network with each other router present in the network.
3. Updating the path on its own and rerouting the best possible path.

Components

There are three main components that were used in dynamic routing:

1. Data structure ( to structure information )
2. Algorithm ( to construct or re-update path )
3. The routing protocol ( to share information about the network )

Advantages

1. Beneficial in Performance as well as scalable networking with a high frequency of data on nodes.
2. Makes fewer mistakes as it reroutes itself compared to other routing protocols.
3. No need to be manually configured by the admin.
4. Shares information about the network with each other makes them more reliable to work efficiently.

Disadvantages

1. Requires more heavy and reliable powerful hardware.
2. Higher maintenance compared to static protocol

Dynamic routing protocols play an important role in today’s networks. The following sections describe several important benefits that dynamic routing protocols provide. In many networks, dynamic routing protocols are typically used with static routes.

The Evolution of Dynamic Routing Protocols (3.1.1.1)

Dynamic routing protocols have been used in networks since the late 1980s. One of the first routing protocols was Routing Information Protocol (RIP). RIP version 1 (RIPv1) was released in 1988, but some of the basic algorithms within the protocol were used on the Advanced Research Projects Agency Network (ARPANET) as early as 1969.

As networks evolved and became more complex, new routing protocols emerged. The RIP routing protocol was updated to accommodate growth in the network environment, into RIPv2. However, the newer version of RIP still does not scale to the larger network implementations of today. To address the needs of larger networks, two advanced routing protocols were developed: Open Shortest Path First (OSPF) and Intermediate System-to-Intermediate System (IS-IS). Cisco developed the Interior Gateway Routing Protocol (IGRP) and Enhanced IGRP (EIGRP), which also scales well in larger network implementations.

Additionally, there was the need to connect different internetworks and provide routing between them. The Border Gateway Protocol (BGP) is now used between Internet service providers (ISPs). BGP is also used between ISPs and their larger private clients to exchange routing information.

Table 3-1 classifies the protocols.

Table 3-1 Routing Protocol Classification

With the advent of numerous consumer devices using IP, the IPv4 addressing space is nearly exhausted; thus, IPv6 has emerged. To support the communication based on IPv6, newer versions of the IP routing protocols have been developed, as shown by the IPv6 row in Table 3-1.

RIP is the simplest of dynamic routing protocols and is used in this section to provide a basic level of routing protocol understanding.

Purpose of Dynamic Routing Protocols (3.1.1.2)

Routing protocols are used to facilitate the exchange of routing information between routers. A routing protocol is a set of processes, algorithms, and messages that are used to exchange routing information and populate the routing table with the routing protocol’s choice of best paths. The purpose of dynamic routing protocols includes:

• Discovery of remote networks
• Maintaining up-to-date routing information
• Choosing the best path to destination networks
• Ability to find a new best path if the current path is no longer available

The main components of dynamic routing protocols include:

• Data structures: Routing protocols typically use tables or databases for their operations. This information is kept in RAM.
• Routing protocol messages: Routing protocols use various types of messages to discover neighboring routers, exchange routing information, and perform other tasks to learn and maintain accurate information about the network.
• Algorithm: An algorithm is a finite list of steps used to accomplish a task. Routing protocols use algorithms for facilitating routing information and for best path determination.

Figure 3-1 highlights the data structures, routing protocol messages, and routing algorithm used by EIGRP.

Figure 3-1 Components of Routing Protocols

The Role of Dynamic Routing Protocols (3.1.1.3)

Routing protocols allow routers to dynamically share information about remote networks and automatically add this information to their own routing tables.

Routing protocols determine the best path, or route, to each network. That route is then added to the routing table. A primary benefit of dynamic routing protocols is that routers exchange routing information when there is a topology change. This exchange allows routers to automatically learn about new networks and also to find alternate paths when there is a link failure to a current network.

Compared to static routing, dynamic routing protocols require less administrative overhead. However, the expense of using dynamic routing protocols is dedicating part of a router’s resources for protocol operation, including CPU time and network link bandwidth. Despite the benefits of dynamic routing, static routing still has its place. There are times when static routing is more appropriate and other times when dynamic routing is the better choice. Networks with moderate levels of complexity may have both static and dynamic routing configured.

Page 2

Routing tables can contain directly connected, manually configured static routes and routes learned dynamically using a routing protocol. Network professionals must understand when to use static or dynamic routing. This section compares static routing and dynamic routing.

Using Static Routing (3.1.2.1)

Before identifying the benefits of dynamic routing protocols, consider the reasons why network professionals use static routing. Dynamic routing certainly has several advantages over static routing; however, static routing is still used in networks today. In fact, networks typically use a combination of both static and dynamic routing.

Static routing has several primary uses, including:

• Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly.
• Routing to and from a stub network, which is a network with only one default route out and no knowledge of any remote networks.
• Accessing a single default route (which is used to represent a path to any network that does not have a more specific match with another route in the routing table).

Figure 3-2 provides a sample static routing scenario.

Figure 3-2 Static Routing Scenario

Static Routing Scorecard (3.1.2.2)

Static routing is easy to implement in a small network. Static routes stay the same, which makes them fairly easy to troubleshoot. Static routes do not send update messages and, therefore, require very little overhead.

The disadvantages of static routing include:

• They are not easy to implement in a large network.
• Managing the static configurations can become time consuming.
• If a link fails, a static route cannot reroute traffic.

Table 3-2 highlights the advantages and disadvantages of static routing.

Table 3-2 Static Routing Advantages and Disadvantages

Using Dynamic Routing Protocols (3.1.2.3)

Dynamic routing protocols help the network administrator manage the time-consuming and exacting process of configuring and maintaining static routes.

Imagine maintaining the static routing configurations for the seven routers in Figure 3-3.

Figure 3-3 Small Dynamic Routing Scenario

What if the company grew and now has four regions and 28 routers to manage, as shown in Figure 3-4? What happens when a link goes down? How do you ensure that redundant paths are available?

Figure 3-4 Large Dynamic Routing Scenario

Dynamic routing is the best choice for large networks like the one shown in Figure 3-4.

Dynamic Routing Scorecard (3.1.2.4)

Dynamic routing protocols work well in any type of network consisting of several routers. They are scalable and automatically determine better routes if there is a change in the topology. Although there is more to the configuration of dynamic routing protocols, they are simpler to configure in a large network.

There are disadvantages to dynamic routing. Dynamic routing requires knowledge of additional commands. It is also less secure than static routing because the interfaces identified by the routing protocol send routing updates out. Routes taken may differ between packets. The routing algorithm uses additional CPU, RAM, and link bandwidth.

Table 3-3 highlights the advantages and disadvantages of dynamic routing.

Table 3-3 Dynamic Routing Advantages and Disadvantages

Notice how dynamic routing addresses the disadvantages of static routing.