Using a dynamic routing protocol in a network today is a common routing strategy for providing full network connectivity in enterprise environments. Simultaneously, it has many advantages over static routing and brings many additional benefits, especially in medium to large networks.
However, there are several dynamic routing protocols available on the market, and choosing the most appropriate one is essential. Which one you choose depends on many different criteria such as the size of the network, the topology used, the presence of redundant links and equipment, the types of applications running, and similar related criteria that might be crucial for the protocol selection.
Thankfully, the selection process is quite simple, but it requires a good background of the characteristics of each of the routing protocols. Once all that information is known, the selection of the dynamic routing protocol can begin.
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In this article, we will discover the characteristics of the internal routing protocols such as RIP, EIGRP, OSPF, and IS-IS. We will then compare these routing protocols to find out how you can use that information when choosing a routing protocol for your network.
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Before we dive into the characteristics, features, and behavior of each protocol, we must first understand the differences between the dynamic routing protocol types.
On one hand, we have the distance vector protocols such as RIP and EIGRP, while on the other, we have the link-state routing protocols, such as OSPF and IS-IS. There are also exterior gateway protocols such as path vectors, but we won't focus on those in this article.
Distance vector protocols determine the direction and distance to any link in the network. The way they learn about parts of the network is based on rumor because each router learns only from directly connected neighbors, instead of the source where the information originated.
Therefore, when a router sends data to a certain destination, it only knows the exit interface that should be used and how far the destination is but contains no knowledge about the full route that will be used.
In contrast, link-state routing protocols learn network information from the source, instead of from the neighbors and always know the exact route that will be used when packets are sent to a certain destination.
Even though EIGRP is based on the distance vector protocol type, it uses some link-state features, so it is considered to be an advanced distance vector protocol, also known as a hybrid protocol.
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Although all internal routing protocols have the same goal, which is learning about different parts of a network, they do not use the same approach or follow an identical behavior. For that reason, we will look at various individual characteristics of each protocol to determine the most suitable one in certain use cases.
Configuring RIP is a very easy process and does not require any special knowledge to implement. All you will have to do is configure a few commands on the Layer 3 devices (usually routers) and your network should become functional.
Likewise, EIGRP supports easy setup, but it is a little bit more difficult than RIP because of the additional features it supports and the more advanced approach it uses.
On the contrary, both OSPF and IS-IS use the same algorithm, so their procedure is quite similar. However, compared to RIP and EIGRP, the setup itself is more complicated, and additional recommendations must be followed to properly implement them.
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When using RIP and EIGRP you do not have to be afraid of new routers that are connected to the network. Their approach is very flexible, so you can add additional routers whenever and wherever you want.
To a certain point, IS-IS is similar to these two protocols, but not at the same level because of the more challenging implementation approach. OSPF is quite rigid regarding its design and, therefore, it is important to have a proper network design in place before implementing OSPF.
RIP is designed in a way that allows it to be used only in small and simple networks. At the same time, RIP is considered a legacy protocol according to today’s standards because of the limitations and drawbacks it has. After all, RIP was developed a very long time ago, when networks were extremely simple, and different criteria were sufficient for proper routing.
EIGRP and OSPF are the best choice for medium to large networks, even though OSPF is a better option because it has been a standard routing protocol for a longer period.
Although IS-IS is using the same algorithm as OSPF, it uses a different configuration approach and is designed for extremely large networks. Usually, you will see IS-IS implementation in large service providers.
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Updates play a key role in the learning process of the networks, so it is quite important how each protocol approaches this matter. RIP sends updates every 30 seconds by default and this method consumes a lot of unnecessary bandwidth and processing resources.
On the other hand, EIGRP, OSPF, and IS-IS send trigger updates only when there is a network change, and this results in more optimized routing. On top of that, OSPF routers exchange a summary of the routing table every 30 minutes, as additional database synchronization.
When a network change happens, routers must quickly adapt to those changes, so you will not experience any network connectivity problems. However, not all routing protocols react in the same way.
RIP, for example, is the slowest because of its old design. On the contrary, OSPF and IS-IS are considered to have fast convergence by default and with additional tuning, they can converge even faster.
By far, the winner in this category is EIGRP because of the diffusing update algorithm (DUAL) it uses and its unique approach that allows extremely short convergence times when some requirements are met.
For additional redundancy and bandwidth, you can always use load balancing. For that reason, all routing protocols support equal load balancing that allows several equally valued routes to a single destination network to be used in the routing table at the same time.
However, EIGRP goes one step further and supports unequal load balancing that allows routes with different metrics to the same destination to also be included in the routing table. By default, this feature is off, but you can enable it when needed.
Because of the IPv6 popularity, all routing protocols were either modified or evolved into new versions, so all of them can function within IPv6 networks.
However, there are some differences regarding the configuration approaches used by each of them, but in the end, they all function similarly as they do in IPv4 networks.
One of the disadvantages of using a dynamic routing protocol is the additional consumption of CPU, memory, and bandwidth. Therefore, it is important to be familiar with the resource efficiency of each type.
RIP is the least efficient protocol because of the way it functions when sending updates and performing convergence. OSPF and IS-IS are more efficient and satisfy today’s standards and can even be improved with additional tuning.
EIGRP is the most efficient routing protocol due to the way it was constructed to function when certain requirements are met.
RIP and EIGRP are routing protocols that you will seldom see being implemented in a service provider. OSPF is the common choice for internal routing inside service providers, while IS-IS is the preferable option for extremely large provider networks, where flexibility is important.
It is a fact that OSPF is the most popular routing protocol today, not just in enterprise networks, but in service providers as well. The big brother, IS-IS protocol, will most likely never have a chance against OSPF or EIGRP as a routing option for a production network.
RIP hand is rarely used because of its limitations, while EIGRP is the most popular in networks with Cisco equipment, although it has been standardized several years ago.
|
Characteristics |
RIP |
EIGRP |
OSPF |
IS-IS |
|
Implementation |
Very easy |
Easy |
Difficult |
Difficult |
|
Design |
Flexible |
Flexible |
Rigid |
Somewhat flexible |
|
Scalability |
Small networks |
Medium to large networks |
Medium to large networks |
Large to extremely large networks |
|
Updates |
Every 30 seconds |
Trigger updates |
Summary every 30 min and trigger updates |
Trigger updates |
|
Convergence |
Medium |
Extremely fast |
Fast |
Fast |
|
Load balancing |
Equal |
Equal and unequal |
Equal |
Equal |
|
IPv6 Support |
RIPng |
EIGRP for IPv6 |
OSPFv3 |
IS-IS for IPv6 |
|
Resource Efficiency |
Not efficient |
Most efficient |
Efficient |
Efficient |
|
Provider Support |
Not likely supported |
Less likely supported |
Most likely supported |
Most likely supported in large service provides |
|
Popularity |
Not popular |
Popular |
Very popular |
Popular only in large service providers |
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As you can see, prior research of a routing protocol is required before you can decide on the best option. OSPF will most likely be the winner for most use cases, but, depending on certain criteria, EIGRP might be implemented as well.
RIP is the least used protocol, and, except for being used in small networks or some unusual use cases, it will never be a preferred choice. Finally, IS-IS, with its unique approach and addresses that it uses, is an appropriate solution for extremely large networks, but not the best fit for everyday networking.
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