I'm probably overthinking this.... Quick question.

Fernling306

So I am a little confused.
If I have 2 devices on the same network, do/will they always have the same subnet mask or can one of the devices be /26 and the other /28?

I just got done learning how to subnet and started going through some subnetting practices and came up with this question.
Thank you very much.

Edit.
I am really confused now because my question doesn't even make sense to me haha. I am going to post the picture with the question in a moment in hopes that someone will explain it to me.
There are two different masks in the network, so I am unsure of which to work with to find the subnet C info. Please bear with me here I am still very new to everything networking.



1. Take a look at the network diagram below. Which of the following IP addresses would be valid to assign to interface Fa0/2 on the router? (Choose all that apply)




Possible answers:
A. 172.16.12.14
B. 172.16.12.33
C. 172.16.12.152
D. 172.16.12.104
E. 172.16.12.95


Another edit.
I see that they are completely different networks now, didn't really pay attention to the router(haven't gotten into routers yet). I'm not entirely sure I understand how to do this and I have went through all the subnetting that is offered in ICND1 CBT. Is it possible that this question is a bit more advanced than that? Possibly ICND2 or CCNP?

ptilsen

I think you are overthinking it.

255.255.255.240 = 16 IPs, so 172.16.12.0 - 172.16.12.15
255.255.255.192 = 64 IPs, so 172.16.12.64 - 172.16.12.127

The question does not specify what subnet mask C should have. This means to have a "valid" subnet, it must simply not fall within the existing ranges. "A." falls within the range of subnet A, while "D." and "E." fall within the range of subnet B. "C." is well past the range of subnet B, and "B." is after subnet A and before subnet B. "B." could be using a /27 or a /28, and exist as a valid subnet. Similarly, "C." could be as low as /25 and exist as a valid subnet. Either "C." or "B." are valid answers.

Edit: To answer this question, you'll need to read up on variable length subnet masking. The answer to your question is yes, you can have two subnets on the same routed network with different subnet masks, so long as they don't have overlapping addresses.

Fernling306

Hmm I kind of see it now. Most definitely done a bit different than I have seen through CBT icnd1.
Thank you very much for the response.

Roguetadhg

Rep Earned!

I like questions like these. They help me, Im sure there's others that tried to do this problem in their head as well.

sizeon

The anwser could be B,C,E

ptilsen

sizeon wrote: »

The anwser could be B,C,E

E. falls within subnet B and as such is not a valid subnet.

ciscoman2012

I used to have trouble on questions like these as well.

What I do is find the Broadcast, Network #, and range of addresses for the Networks w/ Masks that they do give me. Then I cross off the answers that fall within those ranges.

sizeon

LMAO i didnt see the network address of the interfaces. My fault, i was looking at the ip address of the host only.

Fernling306

ciscoman2012 wrote: »

I used to have trouble on questions like these as well.

What I do is find the Broadcast, Network #, and range of addresses for the Networks w/ Masks that they do give me. Then I cross off the answers that fall within those ranges.

That sounds like a great way to do it, thanks!