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Subnetting Question

I am completely lost with question 5 and 6 as linked below.

https://i.imgur.com/tDittXt.png

I am not sure what a subnet broadcast is as well as how to find a subnet number and address.

Any help is very appreciated!

7 comments
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Hello! I'm going to start with question 6 because i'm still trying to figure out what they are asking with question 5. So... 6:

210.10.10.114 with a 30 bit subnet mask (that mask being 255.255.255.252). They are asking what is the subnet number and what addresses belong there.

For a /30 you increment the Network ID every 4 because you only got 2 bits for the host part, and therefore, 22 equals 4. So you start with 210.10.10.0 and keep adding 4:

210.10.10.0 - 210.10.10.4 - 210.10.10.8 - ... - 210.10.10.108 - 210.10.10.112 - 210.10.10.116

Right here you can already see that your IP belongs in between those 2 last network IDs. Therefore you got all the info you need. I assumed you were already familiar with subnetting mechanics, so let me know what else you need!

  • Network ID: 210.10.10.112

  • First available IP: 210.10.10.113

  • Last available IP: 210.10.10.114

  • Broadcast ID: 210.10.10.115

Does this help? Or you need help with the subnetting math to figure things out?

Original Poster1 point · 3 months ago

Thank you so much for this explanation it definitely makes sense!

And yes your assumption that I was familiar with subnetting mechanics is correct :)

This is an excellent sample to use as a reference if anyone is learning how to find the subnet range!

For 5.

255.224.0.0 on the subnet mask means we have 3 bits being used for the mask and 5 bits for hosts. Ignore the other 2 octets for now, the 224 is known as the interesting octet. The questions says 255.223.255.255 is our broadcast which is the very last address in the range before the start of the next subnet. Looking at the 5 host bits we get 2^5 hosts or 32 per subnet. Given that the next subnet is (dont confuse with the mask) 255.224.0.0 just take 224 and subtract 32 from it, this means our Subnetwork is 255.192.0.0

TLDR

Subnet 255.192.0.0 with mask 255.224.0.0

Range 255.192.0.0 -> 255.223.255.255

Host Range 255.192.0.1 -> 255.223.255.254

Original Poster1 point · 3 months ago

Thanks, wish my teacher was as good at explaining as you guys are haha

255.192.0.0-255.223.255.255 is the range on question 5, I think. But have been practicing subnetting for less than a month.

Now with more Cisco!
1 point · 3 months ago

5 Doesn't make sense. 240.0.0.0/4 is reserved, and so 255.223.255.255 can't be any address in any network.

Assuming you ignore that fact, however, a broadcast address is masked just like any other network address:

255.225.0.0 is a /11, so the network address is 255.31.0.0/11

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