Dynamic Routing Protocols Types and their Details

In my previous post, we discussed what routing is and who does it work. In this article, we will focus on understanding Dynamic Routing Protocols types. How many commonly used routing protocols are out there, and how can they be grouped. We will also examine their functions, advantages, and disadvantages. In the upcoming posts, we will dive deep into each type of routing protocol separately.

What are the Routing Protocols in Computer Networks?

Routing protocols are the protocols used by routers to exchange routing information with other routers. This information is further used to build a routing table used by the router to find the best path to use and make appropriate forwarding decisions. A routing protocol also defines how routers communicate with each other, how they share information about the network, and how they update their routing tables.

There are mainly two types of routing protocol: static and dynamic. In Static routing, the network administrator manually configures the route information. However, in Dynamic routing, the routers exchange routing information with each other and automatically update their routing tables.

What is the purpose or role of Routing Protocols?

Routing protocols are rules governing how routers communicate with each other. Routing protocols allow routers to find the best path for data packets to travel automatically by exchanging information about the network. This makes routing more efficient and reduces the chance of errors.

Routing protocols enable routers to exchange information about remote networks and automatically incorporate it into their routing tables.

Routing protocols help to select the most efficient path or route to each destination network. This route is then registered in the routing table. When there is a change in network topology, routers share routing information, which is one of the primary advantages of dynamic routing protocols. This sharing allows routers to learn about new networks automatically and identify backup paths when there is a problem with the current network.

In contrast to static routing, dynamic routing protocols require less attention from administrators. However, using dynamic routing protocols comes at the cost of devoting some of a router’s resources to protocol operation, including CPU time and network link bandwidth. However, there are situations when static routing is more appropriate than dynamic routing; for example, putting a default route is sometimes easier than configuring a dynamic routing protocol. In reality, you can find static and dynamic routing configured in networks that are not too complex.

How do Routing Protocols Work?

By using routing protocols, routers can communicate with each other and share routing data. No matter how varied the routing protocols may be on a granular level, they all serve the same purpose of routing packets from one point to another.

Routers learn about new destinations and discard old information by exchanging routing information with other routers using a routing protocol. A routing protocol defines the format of the messages that are exchanged between routers and the procedures that determine how these messages are exchanged. This way, all routers can keep their routing tables up-to-date and know how to reach all destinations on the network.

Routing protocols build a routing table that is stored in each router and provide information about how to get to various network destinations. Each time a packet is received, a router first checks the packet’s destination address and then consults its routing table to determine how it should be sent.

If the router knows how to reach the destination, it will send the packet to another router that it knows about until the packet eventually reaches its destination. If it does not know how to reach the destination, either it will drop the packet or send it towards the default route or gateway (if one is configured). Then is default gateway’s job is to route the packet or drop the packet further.

Goals of Routing protocols:

The primary goal of routing protocols is to ensure that all routers have accurate and up-to-date information about the network to make the best decisions about how to route traffic.

Routing protocols also aim to reduce network traffic by determining the most efficient path between two points.

Common Routing Protocols Categories:-

Depending on factors like the algorithm used to calculate the best route and how much of the network a routing protocol can span, etc.

You can categorize routing protocols into three groups, each with its own set of common protocol types.

Distance vector, link-state, and Hybrid Protocols

Distance vector protocols use the Bellman-Ford algorithm and measure distance in hops to calculate the shortest path to a destination. The number of hops is equivalent to the number of routers the data passes through before it reaches its destination. The Routing Information Protocol (RIP) is the most common distance vector protocol.

Link-state protocols, on the other hand, use the Dijkstra algorithm and create a map of the network with nearby routers running the same routing protocol. Link-state protocols calculate the shortest path to a destination by measuring the speed of the links and the total cost of the path to a destination. In Addition, Link-state protocols calculate the best path to a destination by considering all available paths. The most common link-state protocol is Open Shortest Path First (OSPF).

Lastly, Hybrid protocols are designed to take advantage of the best features of both distance vector and link-state routing protocols. One example is EIGRP, which uses a combination of these two methods and it is a Cisco proprietary protocol.

Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP)

We can select routing protocols based on the Administrative domain in this category. IGP exchanges routing information between hosts within a single network or administrative domain. On the other hand, EGP is used to exchange routing information between different networks or administrative domains.

Interior gateway protocols connect routers in the same autonomous system; this might be a single routing network or a group of networks under the control of a single company or authority. IGP permits information exchanges within the same internal network without exterior routers. RIP, OSPF, IS-IS, EIGRP are IGPs.

Exterior gateway protocols (EGPs) facilitate communication between routing networks in different autonomous systems. This process is typically more complex than communication between networks within the same system, as it often requires computer networks to communicate outside their default systems. As a result, EGPs are less commonly used than other protocols that only communicate within the same system. Common EGP is BGP.

Classful and Classless protocols

Classful and classless protocols are two different ways of allocating IP addresses. Classless routing protocols do not make assumptions about the network based on the IP address class, while classful routing protocols do. As a result, classless routing protocols can support variable-length subnet masks (VLSM), while classful routing protocols are not.

• Classful protocols update routing tables without subnet masks. Because they identify entire networks and not IP addresses, they omit subnet mask information. 
• Classful protocols presume that all networked devices share the same subnet mask. 
• Classful protocols also use more bandwidth since they update routing frequently. 
• This classification is obsolete nowadays because it supports fewer protocol types.

On the other hand, 

• Classless protocols transfer more detailed data by including subnet mask information in routing updates, which results in better route manipulation by routers. 
• For example, you can create a /24 subnet for all hosts and a /26 subnet for all servers. This would allow you to route traffic more efficiently because you would not have to send as much data in routing updates. 
• Classless protocols also utilize less bandwidth because they only send updates when there is a change in data.
•  Classful protocols are the standard and are used everywhere.

Examples of routing protocols – Dynamic routing protocols types explained

Routing protocols are used to exchange routing information between network devices.

Some common types of routing protocols are:-

• RIP (Routing Information Protocol)
• IGRP (Interior Gateway Routing Protocol)
• EIGRP (Enhanced Interior Gateway Routing Protocol)
• OSPF (Open Shortest Path First)
• EGP (Exterior Gateway Protocol)
• BGP (Border Gateway Protocol)
• IS-IS (Intermediate System to Intermediate System)

Let us look at them briefly in this post.

Routing Information Protocol (RIP)

RIP stands for Routing Information Protocol, an early Interior gateway protocol. RIPv2 helps smaller networks or LANs because it only supports 15 hops or fewer. RIPv1 and RIPv2 are their two versions.

Below are some of the Characteristics of RIP:-

• RIPv1, the initial version, estimates network routes based on hops (not more than 15) to a pre-determined destination.
• RIPv1 broadcasts its IP address to other networks.
• RIPv1 is obsolete.
• On the other hand, RIPv2 shares its routing table using a multicast address to identify the main computer network.
• RIPv2 incorporates data security methods like plain text and md5 authentication.

Advantages and Disadvantages of RIPv2:-

Advantages of RIPv2:

• RIPv2 is an enhanced version of RIPv1 and supports classless inter-domain routing (CIDR).
• It also supports variable-length subnet masks (VLSM).
• Unlike RIPv1, it does not broadcast the entire routing table but only sends updates about changed routes. This reduces network traffic.
• It uses authentication to prevent malicious updates from being accepted.

Disadvantages of RIPv2:

• RIPv2 is slower than other dynamic routing protocols such as OSPF because it uses periodic updates instead of triggered updates.
• It has a limited hop count of 15, which limits its usefulness in large networks.

I will be writing an entire post on RIP and other protocols in upcoming posts.

Interior Gateway Routing Protocol (IGRP)

IGRP is Cisco proprietary.

Below are some of the Characteristics of IGRP:-

• It employs RIP’s core functionalities but supports 100 hops. It can support larger networks when compared to RIP.
• IGRPs are classful, distance-vector protocols.
• IGRP also compares network capacity, reliability, and load.
• Like other dynamic protocols, it updates its routing table automatically when route changes occur, preventing routing loops.
• IGRP is also obsolete and not used anymore in networks.

Enhanced Interior Gateway Routing Protocol (EIGRP)

EIGRP is a hybrid routing protocol and combines aspects of both link-state and distance vector routing protocols.

Characteristics of EIGRP Include:-

• It is a Cisco proprietary protocol, meaning you can only use it on Cisco routers.
• EIGRP is a very efficient and scalable routing protocol that can be used in small to large network environments.
• EIGRP is an enhanced version of IGRP.
• EIGRP is a hybrid, an interior gateway, and a classless protocol.
• EIGRP supports 255 hops.
• EIGRP uses the Diffusing Update Algorithm (DUAL) to calculate the shortest path to a destination.

Advantages and Disadvantages of EIGRP:-

Advantages of EIGRP:-

• EIGRP is a fast protocol and uses the Diffusing Update Algorithm (DUAL) to find the best path to a destination network.
• EIGRP is a very scalable protocol. It can support up to 16,000 routes in a single autonomous system.
• EIGRP uses minimal bandwidth and CPU resources. It sends only updates when there is a change in the network topology.
• EIGRP supports multiple network protocols such as IP, IPX, and AppleTalk.

Disadvantages of EIGRP:-

• EIGRP has a complex configuration and is difficult to troubleshoot.
• EIGRP uses more network resources than other routing protocols.
• EIGRP is proprietary to Cisco and is not compatible with other vendors’ equipment.

Open Shortest Path First (OSPF)

Open Shortest Path First (OSPF) uses a link-state routing algorithm and is widely considered to be one of the most robust and scalable routing protocols. As a result, OSPF is often used in large enterprise networks.

Characteristics of Open Shortest Path First (OSPF) include:-

• OSPF is a link-state routing protocol and an IGP.
• OSPF uses the shortest path first (SPF) algorithm to calculate the best route for data packets.
• OSPF is also a classless routing protocol that can support multiple network masks and address ranges.
• OSPF sends updates only when there is a change in the network topology.
• OSPF converges quickly after a change in the network topology.
• OSPF is capable of load balancing across equal-cost paths.

Advantages and Disadvantages of OSPF:-

Advantages of OSPF:-

• OSPF is a link-state routing protocol that uses the shortest path first algorithm to calculate the best route for data packets; this ensures that data packets are routed efficiently and quickly.
• OSPF supports multiple equal-cost paths, which provides load balancing and redundancy.
• OSPF has low overhead and is therefore efficient.
• OSPF is scalable and can be used in small and large networks.

Disadvantages of OSPF:-

• OSPF requires more configuration and setup than other routing protocols such as RIP.
• OSPF uses more network resources than other routing protocols, such as RIP.
• OSPF can be complex to configure and troubleshoot.
• OSPF converges slowly after a network change.

Border Gateway Protocol (BGP)

The Border Gateway Protocol (BGP) is the core routing protocol of the Internet. It is the exterior gateway protocol (EGP) used to exchange routing and reachability information among autonomous systems (AS) on the Internet. 

Characteristics of Border Gateway Protocol (BGP) include:-

• BGP is a path vector protocol that uses AS numbers to identify the path that traffic should take to reach its destination.
• BGP is a policy-based routing protocol, so administrators can configure it to prefer certain routes over others.
• BGP is a scalable protocol, which means you can use it in small and large networks.
• BGP is a robust protocol which means it is designed to be resistant to outages and other problems.
• BGP has two types namely – External BGP (eBGP) , Internal BGP (iBGP)
• eBGP – External BGP is used to exchange routing information between different autonomous systems.
• iBGP – Internal BGP is used to exchange routing information within the same autonomous system.

Advantages and Disadvantages of BGP:-

Advantages of BGP:-

There are many advantages of BGP, some of which are listed below:

• BGP allows for more specific routing than other protocols, meaning you can direct traffic more efficiently.
• BGP is less likely to experience routing loops than other protocols.
• BGP supports multiprotocol routing, meaning that you can use it to route traffic for multiple protocols (such as IPv4, IPv6, VPNV4, and VPNV6).
• BGP is designed to scale to large networks, making it suitable for use in enterprise environments or on the Internet.

Disadvantages of BGP:-

Some of the main disadvantages of BGP include:

• BGP can be complex to configure and troubleshoot.
• BGP requires more memory and CPU resources than other routing protocols.
• BGP is not well suited for small networks.
• BGP is vulnerable to certain types of attacks.

Intermediate System to Intermediate System (IS-IS)

IS-IS is a link-state protocol that uses a topological map of the network to determine the best route for data packets.

Characteristics of Intermediate System to Intermediate System (IS-IS) include:-

• IS-IS is a link-state routing protocol.
• IS-IS uses the shortest path first algorithm to calculate the best route to a destination network.
• IS-IS supports variable-length subnet masks (VLSM).
• It is capable of load balancing across equal-cost paths.

Advantages and Disadvantages of IS-IS:-

There are several advantages to using IS-IS:

• IS-IS is designed specifically for use in large networks, making it more scalable than other protocols.
• IS-IS uses a link-state routing algorithm, which provides faster and more accurate routing than Distance Vector protocols.
• IS-IS supports multiple network layer protocols, making it more versatile than other protocols.
• IS-IS can run over various media types, including Ethernet, Token Ring, and ATM.

There are a few disadvantages of IS-IS, which include:

• IS-IS does not scale well in very large networks.
• IS-IS is not as widely adopted as other routing protocols, such as OSPF or BGP.
• IS-IS can be complex to configure and troubleshoot.
• IS-IS does not fully support equal-cost multi-path routing (ECMP), so load balancing across multiple paths is not very effective.

What is the difference between forwarding and routing?

The main difference between forwarding and routing is that forwarding is the process of moving packets from one network node to another or one router’s interface to another. While routing is the process of gathering all the known networks and their destinations and then finding the best path for those packets to take to reach the destination.

Routing Protocols and Administrative Distance

You can refer to the below table for routing protocols and their Administrative Distance (AD).

Lower AD is preferred in Cisco Devices.

Conclusion

In conclusion, types of dynamic routing protocols can be broadly grouped into IGP and EGP; IGP is further divided into distance-vector, link-state, and hybrid routing protocols, and EGP has only one protocol which is BGP. Each routing protocol has its own advantages and disadvantages, but the choice of protocol is ultimately up to the network administrator.

Frequently Asked Questions (FAQs)

• About
• Latest Posts

Afroz Ahmad

I'm Afroz, a Network Engineer and CCIE with 17 years of experience in Computer Networking, Data Centers, Telecom, Internet Services and ISPs. Currently, I work as a Network Designer for a leading ISP equipment vendor. I share my expertise through my blog and courses, aiming to share my knowledge and simplify complex networking concepts for both beginners and experienced professionals.

Latest posts by Afroz Ahmad (see all)

• Netgear Router Red Light: Causes & Fixes[With Infographic] - April 5, 2024
• Modem vs Router: Understanding the Key Differences - April 5, 2024
• 10 Best Routers for Large Homes: Ultimate Coverage & Speed (2024 Guide) - April 4, 2024