Problem with subnetting in interfaces between routers

[elker_7777777]

I have been asked to configure a network in packet tracer using the network address 192.168.10/24

The given network has 4 routers connected in a square, each with a network of PCs/Servers connected to it.

I was asked to create a "separate subnet for each of the following groups:

-network A- 100 PCs

-network B- 60 PCs

-network C- 15 servers

-4 segments for the backbone links between the routers

"

So I tried using subnets of 255...128, ...192, ...224, and ...240 for those 4 groups

but when I try to give 2 interfaces on the same router an IP address within the same subnet (i.e. ...240) it tells me it "overlaps" with the other one.

(I don't understand why this is happening, and that could be my first question)

so I thought about giving each link between the routers 2 IP addresses in a separate subnet, but as far as I know, I can only create 6 different subnets within the given network.. (...128, ...192, ...224, ...240, ...248, ...252) or am I wrong? (because I assume you cannot use the network/broadcast address in each subnet, and packet tracer also gives me an error for that if I try)

How should I approach this problem? Any help/explanation would be greatly appreciated. I am a student and still learning

Thank you.

[Mark Malone]

Hi

you cant have overlapping subnets that's a general rule as it confuses the router , what you need to do is VLSM and break down the /24 into smaller subnets so there not overlapping

192.168.10.1 - .127 /25 is  for a 126 hosts subnet 192.168.10.0/25

192.168.10.129 - 190 subnet 192.168.10.128/26 62 hosts

192.168.10.193 - 192.168.10.206  subnet 192.168.10.192 /28 15 hosts

https://www.tutorialspoint.com/ipv4/ipv4_vlsm.htm

[elker_7777777]

Yeah, so I've done that already,

I realize now I wasn't very clear in my question

I configured the 3 networks alright, and I didn't have a problem with that. My issue at the moment is with the "4 segments for the backbone links between the routers"

I'm not sure how exactly to set that up... How can I create 4 separate backbones if I cannot use different subnet masks (because I only have 3 subnets available) and can't use the same subnet for all the interfaces?

[Mark Malone]

do you mean the interlinks between the routers ?

you would use /30 subnets taken from the /24 too and then route all the subnets between the routers

[elker_7777777]

Wait.......

So you can create multiple /30 subnets?

I was under the impression you could only have /25, /26, /27, /28, /29, /30
and that they would automatically take (for example /25) x.x.x.1-x.x.x.127 or (/26) x.x.x.129-x.x.x.191

Is that not the case? and if I understand correctly, and I could take multiple /30 subnets, how would the network know the range of the subnet?

So I have /25, /26, and /27 all set up... let's say I configure a /30 subnet in one of the interfaces of one of my routers; does it take the range... x.x.x.225-x.x.x.230?(with .224 network address and .231 broadcast?)

[Mark Malone · Accepted solution]

yes you can split the /24 into whatever you want   , so when you have your host subnets , say whatever is left can be broken down into /30s if you want as long as there not overlapping whats already been used

so if your last subnet was .192 /28 your next subnet would be starting at .208 that could then be used as a /30 with 192.168.10.208/30 as subnet with .209 and 210 as the useable addresses or you could use any other free address space right up to the 254

the whole 24 can be divided up how you want once you don't overlap

[elker_7777777]

OKAAAYY,

Now it makes sense, wow, that was actually a HUGE clear up for me
I had no idea that's how it worked.

Thank you so much for your help, it is GREATLY appreciated.

[Julio E. Moisa]

Hi

After you have used VLSM  to obtain subnets for the hosts, you could use the rest (spare) of subnets to create /30 subnets, you can create many how your subnet allows. if you subnetted for the first /30 (like VLSM), the rest available can be used for the same purpose /30, you dont need to subnetting again.

Also you could use /31 subnets, it is supported on some devices. 

:-)

[Julio E. Moisa]

Please see this document I created previously. It is just an example. Hope it is useful.

:-)