How do routers create a broadcast domain boundary?

How do routers create a broadcast domain boundary?
How do routers create a broadcast domain boundary?

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How do routers create a broadcast domain boundary?

Routers create broadcast domain boundaries by separating network segments based on IP addresses. They control the flow of broadcast traffic, like ARP requests, preventing it from spreading across different subnets. This segmentation helps manage network efficiency and security by confining broadcasts within specific local areas.

Want to know how routers create broadcast domain boundaries? Well, first we need to know what a router is. Second, we need to know the difference between a collision domain and a broadcast domain. And after we can look at how a broadcast domain boundary is created.


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Let’s start.


Even though PC networks have been around for a certain number of years, the advancement in this industry continues to develop every day. We can’t disregard the structure squares of networks, with correspondence models, for example, the OSI model, having 7 layers of activity.

For any individual who is curious about this model, all you want to know is that it fills in as basic language for network devices for conveying between them. Beginning from the top layer, which is the Application layer, down to the base layer, which is the physical layer, the OSI model is the essential mainstay of networking. The Data Link layer, which is otherwise called Layer 2, is the place where exchanging of frames happens. The Network layer, otherwise called Layer 3, is the place where packet routing is performed.

Routing and Switching fill in as the center parts of PC networks as we probably are aware of them today. Even though Layer 2 isn’t liable for steering bundles across networks, it is doubtlessly answerable for switching frames from one switch-port then onto the next, before shipping it off to the upper layers.


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What is a router?

A router is a device that associates at least two packet-switched networks or subnetworks. It serves two essential capacities: overseeing traffic between these networks by sending information data packets to their planned IP addresses and permitting various devices to utilize a similar Internet connection.

There are a few kinds of routers, however, most routers pass information between LANs (local area networks) and WANs (wide area networks).

A LAN is a gathering of associated devices confined to a particular geographic area. A LAN typically requires a single router. A WAN, conversely, is an enormous network fanned out over a tremendous geographic area.

Large organizations and companies that work in various areas, for example, will require separate LANs for every area, which then interface with different LANs to frame a WAN. Since a WAN is distributed over a large area, it regularly requires numerous routers and switches.


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What is a collision domain?

The “Collision Domain” portrays a network where packet collisions can happen when two devices on a common network medium send packets simultaneously.

The impacting bundles are disposed of and should be sent once more, which decreases network speed and efficiency.

For the most part, collisions happen in a hub environment, because each port on a hub is in the same collision domain.

Along these lines, all devices associated with the hub are in a similar crash area and just a single device can send at a time, and all different devices should pay attention to the network to keep away from impacts.

The total network transmission capacity is divided between all devices.

As opposed to hubs, each port on a bridge, switch, or router crash area decreases and takes out the chance of impacts and empowers the devices to utilize the full-duplex correspondence.

The full-duplex communication doubles the speed of the information limit.

What is a broadcast domain?

Single switch with two broadcast domains
Single switch with two broadcast domains | Source:

A broadcast domain is a layer 2 domain where one transmission and the message will be shipped off to everyone in a domain. So assuming that we talk about the broadcast domain. Each LAN network has 1 broadcast domain that is associated with the router.


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So assuming you associate 5 different LAN networks with 5 ports on the router it means that there are 5 broadcast domains. So for each broadcast domain, you can have various switches however have a single router with a port. Allow me to make sense of this with an example. 

Would you be able to tell me the number of broadcast domains there are?

broadcast domain example
broadcast domain example

Allow me to let you know that there are two Hubs associated with the clients and one switch in the middle. There is no Switch. I previously talked about how each port of the switch defines the broadcast domain so in the above model there are two distinct LAN networks associated with 2 different ports of the router. So you can say that there are 2 Broadcast domains in the above image shown.

Creating a broadcast domain boundary

In short, how routers create a broadcast domain boundary:

  • They do not forward broadcast traffic.
  • They only forward broadcasts that are intended for multiple subnets.
  • They forward broadcast only to necessary segments.
  • They listen to and direct broadcast traffic.

Now that we have that out of the way, let’s explain.

As referenced previously, Layer 3 Routers DO NOT advance broadcast. The image below shows how a router can go about as a limit for broadcast domains.

Explaining how Routers Create a Broadcast Domain Boundary
Explaining how Routers Create a Broadcast Domain Boundary | Source:

Although each Layer 2 switch in the image above is its broadcast domain, by associating the change to a switch there is a limit between the two broadcast domains. The situation above however gives Layer 3 routing between the two VLANs so that hosts in VLAN 10 can speak with hosts in VLAN 20 as well as the other way around.


In conclusion, routers do not forward broadcast traffic, and that is how they create a broadcast domain boundary. First, we looked at what routers are and how they work. After, we looked collision domain and broadcast domain. Lastly, we looked into how routers create a broadcast domain with an explanation through an image.