| When you're studying to pass the CCNA exam | | | | a switch will forward a broadcast out every |
| and earn your certification, you're | | | | single port on that switch except the one |
| introduced to a great many terms that are | | | | upon which it was received. However, Cisco |
| either totally new to you or seem familiar, | | | | switches allow the creation of Virtual Local |
| but you're not quite sure what they are. The | | | | Area Networks, or VLANs, that are logical |
| term "broadcast domain" falls into the latter | | | | segments of the network. A broadcast sent by |
| category for many CCNA candidates. | | | | one host in a VLAN will not be forwarded out |
| | | | every other port on the switch. That |
| A broadcast domain is simply the group of end | | | | broadcast will be forwarded only out ports |
| hosts that will receive a broadcast sent out | | | | that are members of the same VLAN as the host |
| by a given host. For example, if there are | | | | device that sent it. |
| ten host devices connected to a switch and | | | | |
| one of them sends a broadcast, the other nine | | | | The good news is that broadcast traffic will |
| devices will receive the broadcast. All of | | | | not be forwarded between VLANs. The bad news |
| those devices are in the same broadcast | | | | is that no inter-VLAN traffic at all is |
| domain. | | | | allowed by default! You may actually want |
| | | | this in some cases, but generally you're |
| Of course, we probably don't want every | | | | going to want inter-VLAN traffic. This |
| device in a network receiving every single | | | | requires the use of a router or other Layer 3 |
| broadcast sent out by any other device in the | | | | device such as a Layer 3 Switch. (Layer 3 |
| network! This is why we need to know what | | | | Switches are becoming more popular every day. |
| devices can create multiple, smaller | | | | Basically, it's a switch that can also run |
| broadcast domains. Doing so allows us to | | | | routing protocols. These switches are not |
| limit the broadcasts traveling around our | | | | tested on the CCNA exam.) |
| network - and you might be surprised how much | | | | |
| traffic on some networks consists of | | | | That router we just talked about also defines |
| unnecessary broadcasts. | | | | broadcast domains. Routers do not forward |
| | | | broadcasts, so broadcast domains are defined |
| Using the OSI model, we find devices such as | | | | by routers with no additional configuration. |
| hubs and repeaters at Layer One. This is the | | | | |
| Physical layer, and devices at this layer | | | | Knowing how broadcasts travel across your |
| have no effect on broadcast domains. | | | | network, and how they can be controlled, is |
| | | | an important part of being a CCNA and of |
| At Layer Two, we've got switches and bridges. | | | | being a superior network administrator. Best |
| By default, a switch has no effect on | | | | of luck to you in both of these pursuits! |
| broadcast domains; CCNA candidates know that | | | | |