eBGP vs. iBGP: What’s the Difference?

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eBGP vs. iBGP: What’s the Difference?

Border gateway protocol, or BGP, is one of the cornerstones of modern networking. The modern internet as it is known would not function without BGP behind the scenes, allowing for communication between systems. BGP is a routing protocol, and it has two separate versions of the protocol. However, eBGP and iBGP are similar in that they provide ideal routing paths for network communications. There are some notable differences between the two protocols as well.

If you’re new to the world of computer networking, it is worth exploring the differences. Understanding the differences between eBGP and iBGP isn’t too difficult, thankfully. Let’s take a closer look at how these protocols function, where you would use them, and which one is better for certain use cases.

eBGP vs. iBGP: Side-By-Side Comparison

Full NameExternal Border Gateway ProtocolInternal Border Gateway Protocol
Route AdvertisementRoutes are advertised to other peers, this is advertised to either eBGP or iBGP neighborsNo routes are advertised
Time-To-LiveTTL is set to 1TTL is set to 255
Use CaseUsed to communicate with external networks, either other organizations or internet service providersUsed for internal communications on a local area network for an organization
Administrative Distance20200
Next Hop BehaviorHop is changed to default to the host router when advertised by an eBGP neighborHops remained unchanged regardless of the route
Topology RequiredNo specific topology necessary to functionRequires local area network to have a full mesh topology
Safeguards for Loop ProtectionUtilizes AS path to prevent loopbacksUses Split Horizon to prevent loopback

As you can tell, these protocols have very different purposes. Keeping this in mind, you can see how they fit into an enterprise network environment and where people might implement them.

eBGP vs. iBGP: What’s the Difference?

These two routing protocols aren’t intended as direct replacements for one another. Instead, they function as partners of sorts when considering routing for an organization. There are some very stark differences in their overall function and their intended usage.

Use Case

Communicating with external networks is eBGP’s primary goal. You won’t be configuring eBGP to communicate between other computers on your organization’s local network. Some of the behaviors you’ll see with eBGP further reinforce its intention to communicate with your ISP. Also, eBGP shares the most effective route for the flow of data between peers sharing the same origin.

Computers on local area networks are going to communicate with each other, think about things like internal emails and the like. This is where iBGP shines, as it provides quick and effective communication between endpoints on local area networks. It has stricter network requirements, but this does come with the added bonus of fewer chances for network collision. Since an organization using iBGP requires a full mesh topology, peers won’t advertise routes to each other. Instead, the point of communication is going to change from computer to computer. As a result, iBGP devises efficient routes for every new point of contact.

Types of network topology
iBGP delivers fast and dependable communication between endpoints on local area networks.

How They Work

With all this in mind, how do these two protocols work? Well, eBGP only functions if the two points of communication are separate autonomous systems, or networks if you’re not hip to the jargon. If you’re looking to communicate with your ISP, or just go on the web, then eBGP is the routing protocol used. There are a few tricks eBGP uses to effectively communicate with external networks. Peers on the same network advertise efficient routes to each other. Clients don’t need to be in a full mesh topology to communicate, which would be a nightmare to configure for the entire internet as it stands. Each hop, or when data flows from one location to another, advertises the route to all peers. Clients from different points of origin will end up sharing the most efficient route if they have the same destination.

Internal communication between machines is another matter. It’s clear that iBGP is excellent for internal communication, but there are strict requirements on how to implement it. Engineers will need to integrate all clients and devices into a mesh topology. A mesh topology is different from a mesh network, instead of providing higher availability it just means all clients and devices are connected. Due to the topology requirements, routes aren’t shared between peers. Instead, entirely new routes are devised on the fly.

Which One to Use and When

If you’re looking to have your clients interact with the web, then eBGP is the only logical choice. This is also true if you’re looking to communicate between different sites, like campus area networks communicating with one another. Note that eBGP works best when communicating between remote sites, rather than an internal network.

If you’re looking to set up a local area network, then iBGP is the only suitable option. The stricter network requirements are likely part of the overall design of the internal network as it sits. While there are a multitude of network topologies any networking student will learn, the mesh topology is the most ubiquitous for good reason.

Types of network topology
A mesh topology means all clients and devices are connected.

eBGP vs. iBGP: 6 Must-Know Facts

  • eBGP has a shorter administrative distance
  • eBGP has a far shorter Time-to-Live for packets once transmitted
  • eBGP allows for communication between Metro Area Networks and Campus Area Networks
  • iBGP allows for communication between clients on a business campus
  • iBGP has no provisions for external communication
  • iBGP has the maximum set value for Time-to-Live when transmitting packets

eBGP vs. iBGP: Which One is Better? Which One Should You Choose?

With these routing protocols, there isn’t necessarily a better or a worse one. Instead, if you are an engineer designing a network you’ll end up using both. They both have their specific place within modern networking and serve as the backbone of inter-device communication. However, eBGP is the only option to speak of when considering external communications between networks. Clients can easily communicate between separate external networks or even just go on the web.

Of course, iBGP is the best choice for internal networks. No one in an organization works in a vacuum, as every effort is collaborative. As such, you’ll need quick and effective communication between all of your clients to directly address their needs. Although iBGP has stricter network requirements, chances are you are implementing those rules by default.

Modern networking requires elegant solutions, and both eBGP and iBGP allow for efficient routes. If you’re new to networking, it helps to learn the different protocols. In practice, however, you’re going to be leaning on these two protocols a great deal when designing networks for an organization.

Frequently Asked Questions

How does eBGP impact scalability?

eBGP is built with scaling in mind, and as such handles it quite well. If you’re connecting between multiple campuses and the web at large, then eBGP is built to handle this multitude of connections coming your way.

iBGP can also scale, but given the network requirements, you are going to have a far larger workload when implementing it.

Is iBGP used for external communications?

iBGP is strictly used for communications between clients on a local area network. If you’re looking for connectivity and efficient routing between external sites, then eBGP is the protocol of choice for that. Given iBGP’s requirement for a mesh network topology, it would be exceedingly difficult to implement it for external communication in any meaningful way.

Can you use eBGP for internal communication?

It can work internally in the sense that you can communicate between separate campuses for the same organization. As for communication within the same local area network, that isn’t really the overall aim of eBGP. It is better suited for external communications and does raise some other concerns given its advertisement of routes to peers in the same domain.

Which protocol is best for my organization?

You aren’t picking and choosing with eBGP or iBGP. If you’re looking to implement efficient routing between endpoints, you’ll end up using both. Your organization is likely going to communicate with external resources, just like it is likely that it’ll communicate with other clients and devices on the same network. As such, these protocols will go hand-in-hand rather than having a choice of the routing protocols.

Why do we need routing protocols?

Having safe and efficient routes enables greater overall communication. If you aren’t having to worry about timed-out connections, packet collisions, and other former ills of networking, then everything is running smoothly. Having a routing protocol handles the dirty work of creating effective communication paths for the devices on your networks, rather than an engineer having to do it all by hand.

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