In networking, a broadcast means that us send something the everyone receives, even if it is they need/want the or not. Switches will forward broadcast traffic on all their interfaces, except the one they got the transfer on. Here’s an illustration come visualize this:


H2 top top the left side sends out a broadcast which is forwarded to all various other switches and also computers. There space a variety of applications and protocols that usage broadcast traffic. A good example is ARP (Address Resolution Protocol). Switches will recognize it as broadcast web traffic by looking at the destination MAC address. Here’s an instance of an ARP request:


Above you have the right to see the the destination MAC resolve is FF:FF:FF:FF:FF:FF.

You are watching: Routers do not forward broadcast packets.

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

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


Broadcast web traffic is not an extremely efficient. For example, let’s say the that ARP inquiry is sent out by H2 to figure out the MAC deal with of H1. The info in the ARP request is useless for SW2, SW3, and also H3 but they execute receive it. SW2 and also SW3 have to waste bandwidth forwarding the transfer frame and also H3 has to waste some CPU cycles come look in ~ an ARP request that it doesn’t treatment about.

Nowadays, CPUs space fast and also we use quick (Gigabit) interfaces therefore the impact of broadcast website traffic is not so bad. About 20 years ago, having a network through a lot of of gadgets could influence your performance because of broadcast traffic. Older operating systems also used a lot of broadcast traffic for their applications.

Broadcast domains with 1-1000 tools are usual nowadays.

Still, a single device that sends a the majority of broadcast web traffic does impact the entire broadcast domain so it’s a great idea to limit the size of her broadcast domains.

How do we develop multiple transfer domains? One means to execute this is by including a router to your network:


Routers, uneven switches, do not front broadcast traffic. As soon as H2 sends out that broadcast frame, it will be forwarded through SW2 come R1 however that’s it. This does typical that traffic from H2 come H1 will have to be routed but that’s another story. Here are the broadcast domain names we have actually now:


We now have actually three transfer domains, one on each side the the router.

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

Normally ~ above a Cisco switch, every interfaces belong to VLAN 1 which means all interfaces are able to communicate with each other. With a VLAN, we have the right to separate this. Because that example, we deserve to put interface 1-9 in one LAN and also interface 10-19 in one more LAN. These two VLANs won’t be able to communicate with each other, producing two various broadcast domains.

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



You have learned what a transfer domain is:

A broadcast domain is a collection of tools that get broadcast web traffic from every other.Switches will forward broadcast website traffic to all interfaces, except the one whereby it originated from.A the majority of broadcast web traffic might impact your network performance so to reduce the dimension of the broadcast domain is something come consider.Routers perform not forward transfer traffic, they break transfer domains.VLANs on switches also allow you to break transfer domains.