How many broadcast domains? Diagram Question CCNA

okay let's look at the dreaded how many broadcast domains question this is a typical question that you'll see in networking tests I mean yeah networking test networking certification exams things like that they're gonna ask you how many broadcast domains well you look at the diagram and you go oh and a lot of people have a hard time with this question so we're gonna we'll break it down and we'll start with a simpler example and we'll show you that actually answering a question like that's pretty easy alright so we'll look at this one we'll look at this one and maybe we should even start with just this one okay so we'll start here first of all when they ask you how many broadcast domains what they're really asking you is how many networks a broadcast domain is a network all right broadcasts are sent throughout a network they oh they don't pass through the network to other networks in other word broadcasts stay stay behind the network or stay behind the firewall or are bound by the router so a router is what contains broadcast domains if you look at this example right here you've got a switch this is a symbol for a switch and a switch right and you've got all these computers right and you have let's say these servers here and let's say let's say this scenario actually looked a little bit more like this right let's say it looked more like this and we were talking about hubs instead of switches right and you know in a scenario like this with hubs if you have broadcasts you could end up with a broadcast storm which is broadcast going just everywhere and even in a such a scenario like this even with the switches broadcasts you could have a broadcast storm so too many broadcasts on the network would decrease performance that's it in the question they always say is well how would you improve performance on this network well first of all if you had hubs right here right one way to improve the network would be to change the hubs into switches and then the other way to improve the network and actually would be to take this single broadcast domain right one broadcast I mean there's no routers it's one network they're all let's say on the 192 168 1 network one way to improve it would be to bring out a router and turn it into 2 separate networks or to broadcast domains now these broadcasts generated by these clients will stay on this network over here and then the broadcast by these servers will stay on this network over here so now instead of one broadcast domain you have to broadcast domains now on the tests they'll confuse you with that because they'll say routers break up broadcast domains well what does that mean routers break up broadcast domains well quite simply what it means is routers create broadcast domains if you have a router you have now have 2 networks and you have to broadcast domains all right so how many broadcast domains in this example 2 how many how many now 1 all right so we go to the next network right another problem that we'll see is people will say well you know if this last example there was two networks right and the router has two interfaces so the number of broadcast domains equals the number of interfaces on the router and yes each interface on the router signifies the network but it doesn't always work out in other words if you have this scenario this router has two interfaces ethernet serial right and you have a scenario where this is a broadcast domain right that land ok this interface this switch this computer they're all in the same network that's a broadcast domain and you have this scenario over here right and that's a broadcast domain this router interface this switch this server right this is a network right but you can't simply count the interfaces because this router is connected to another router and in between the two routers is a third network right if you simply count how many interfaces on the routers one two three four you'll come up with four networks but that's not correct in this case there's only three networks one one in between the two routers and one over here and what does that mean it means that these routers they're on the same network they need to be in the same network address space right if this is 10 0 dot 0 dot 1 this needs to be 10.0.0.0 and look at this example and we can answer it a lot easier and we can get the correct answer so we just count the networks all right this router has an interface right here connected to a switch connected to a client we'll draw a circle and we'll say that's one network one broadcast domain and then we say this router has a interface right here connected to a switch I don't see any clients but still that is let's say a network in between the two routers we've got a network right okay now we've got three networks now what about over here well this router has connected to a hub which is connected to a server and that is a network so there's a fourth broadcast domain or fourth network and now we look at the hard part of the diagram this router is connected to a switch but this switch is connected to another router and this switch is connected to another router well that means that all the devices connected to this switch are on a land in other words they all need the same address space so this is one broadcast domain right in here that's one network these routers would all need the same network address space they'd all need to be on the 192 168 1 Network for instance right or something like that so that's one broadcast domain and now coming off of this router we have a hub and a printer right that's another broadcast domain and then coming off directly connected to this routers Ethernet interface as a server server directly connected to the Ethernet is a crossover cable will say that is a broadcast domain so in this diagram there is one two three four five six seven broadcast domains or seven networks all right I hope this example helps you out a lot on your tests and your certification trials

Channel: danscourses

Views: 106,879

Rating: 4.9405942 out of 5

Keywords: network, diagram, broadcast, domains, examples, Cisco, CCNA

Id: s3pq0bdZMz8

Length: 7min 7sec (427 seconds)

Published: Wed Sep 14 2011