Sorry for the noob question. Just some clarification.

[johnpaulohernaez]

Hello everyone. I just have a question regarding this tutorial I'm watching.. There are 2 ip address in the screenshot, 192.168.2.0 & 192.168.3.0/30.. My question would be, can the two of them exist in 1? Like 192.168.2.0 then the other would be 192.168.2.1 or so on.. I'm sorry for this noob question. 

[Jon Marshall]

Not really sure what you are asking. 

192.168.2.0/30 - 

the subnet is 192.168.2.0,  then you have two useable IPs 192.168.2.1 and 192.168.2.2 and the broadcast is 192.168.2.3. 

Same for the 192.168.3.0/30 subnet. 

Perhaps you can clarify what you mean ? 

Jon

[johnpaulohernaez]

I was just curious on the 192.168.3.0.. Why didn't he just use 192.168.2.1 or other addresses in 192.168.2.0 network?

Why did he make it 192.168.3.0 where in he could just use 192.168.2.1,.2,.3,.4,.5.. 

[Jon Marshall]

Because he needed two subnets for the connections ie. - 

router0  (192.168.2.1)  -> (192.168.2.2) router1 (192.168.3.1)  -> (192.168.3.2) router2 

he could have used a different subnet than 192.168.3.0/30  but he couldn't have used 192.168.2.1/2 because they are in the 192.168.2.0/30 subnet and they are needed as above. 

He could however have used 192.168.2.4/30 and the IPs in that subnet to connect the routers as above would be 192.168.2.5 and 192.168.2.6. 

Jon

[Martin L]

The Rule is that router interfaces must be on different networks /subnets. Or each of L3 interfaces belongs to different network.

You cannot have 192.168.2.1 and 192.168.2.2 on /24 on the same router; it will give you an "overlapping"  error.  Try it to see error.  The goal is to route traffic via different networks or connect networks.  This is main reason for any router.

Another thing is /30 is more of recommendation or good practice rather then a rule itself.  To save address space and IPs Subnetting was born. you do not need to do it in small to medium corporation/design but for any point to point connections (router to router) you only need 2 IPs so /30 is perfect while /24 is too much.  even some uses /31 but I do not know if any Cisco CCNA exam let you do /31.

Regards, ML
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