In networking, a broadcast means that we send something that everyone receives, whether they need/want it or not. Switches will certainly forward broadcast website traffic on all your interfaces, except the one they obtained the transfer on. Here’s one illustration to visualize this:


Above you deserve to see that the destination MAC deal with is FF:FF:FF:FF:FF:FF.

You are watching: How many broadcast domains are in the topology?

Switches will additionally broadcast Ethernet frames if lock haven’t learned the location MAC deal with yet.

A broadcast domain is a repertoire of network tools that obtain broadcast web traffic from each other. Because that example, here’s our network with three switches again:


Broadcast website traffic is not really efficient. Because that example, let’s say the that ARP inquiry is sent by H2 to figure out the MAC resolve of H1. The details in the ARP request is useless because that SW2, SW3, and also H3 yet they execute receive it. SW2 and SW3 have to waste bandwidth forwarding the broadcast frame and H3 has to waste part CPU cycles come look in ~ an ARP request that it doesn’t treatment about.

Nowadays, CPUs room fast and also we use quick (Gigabit) interfaces therefore the affect of broadcast website traffic is no so bad. About two decades ago, having a network with a lot of devices could impact your performance because of transfer traffic. Older operation systems additionally used a many broadcast traffic for their applications.

Broadcast domains with 1-1000 tools are common nowadays.

Still, a single an equipment that sends out a the majority of broadcast web traffic does impact the entire broadcast domain for this reason it’s a good idea to limit the dimension of her broadcast domains.

How execute we produce multiple broadcast domains? One method to perform this is by adding a router to your network:


Routers, unlike switches, execute not forward broadcast traffic. Once H2 sends that broadcast frame, it will certainly be forwarded by SW2 come R1 yet that’s it. This does median that website traffic from H2 to H1 will need to be routed but that’s another story. Below are the broadcast domains we have actually now:


We now have actually three broadcast domains, one on every side that the router.

Is there any kind of option to produce multiple broadcast domain names on a switch? There sure is, it deserve to be done with VLANs (Virtual LAN).

Normally ~ above a Cisco switch, all interfaces belong to VLAN 1 which way all interfaces are able to communicate with every other. Through a VLAN, we have the right to separate this. For example, we deserve to put interface 1-9 in one LAN and also interface 10-19 in an additional LAN. These two VLANs won’t have the ability to communicate with each other, creating two different broadcast domains.

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We will take a closer look in ~ VLANs in an additional lesson but for now, store in mind that it’s a possibility:



You have learned what a broadcast domain is:

A transfer domain is a arsenal of devices that get broadcast web traffic from each other.Switches will forward broadcast website traffic to every interfaces, except the one where it source from.A the majority of broadcast traffic might affect your network performance so to reduce the size of the transfer domain is something to consider.Routers carry out not forward broadcast traffic, castle break transfer domains.VLANs on switches also enable you to break transfer domains.