Subnetting a Subnet

[DistraughtSysop]

just wanting to see if I am correct..255.255.255.240

That would equate to 11111111.11111111.11111111.11110000. The first 28 bits belong to the network and the remaining 4 belong to the host. Converting the network bits to 1s and the host bits to zero, that would equate to 255.255.255.240. Is that correct?

Correct. If you can get that, then it's not hard to get any of them. Consider that any value in an octect is exactly 8 bits away from the same value in the next octet. Compare the subnet masks of /25, /17, and /9. What do you notice?

The rule seems to state that an address beginning with 129 is in the Class B range but when I try to subnet it into 16 networks (2 to the power of 5 or 32), i dont know which part constitutes the beginning of the host part of the address. Does it begin at the 112 (01110000) part of the address or the 0 (00000000) part of the address.

The thing to keep in mind is that, even though it is still referenced, classful addressing is no longer used since it was replaced by CIDR. We still refer to the classes out of convenience and familiarity, but the network and host bits are determined by the subnet mask. This means that, as an example, 10.10.10.0 /24 would not behave as a traditional class A network.

Find the subnet mask of 129.33.112.0/20 and look at it - can you identify which bits are reserved for the network?

Thanks for that. The address I've been given is 129.33.112.0/20. I need to make 16 subnets from this. So if I begin taking bits at the 112 part of the address, I would need to take 5 bits as 2 to the power of 5 is 32-2 = 30. That would allow me to make my 16 networks. Is that correct?

The /20 means that your network is already divided into 16 subnets. The question is to find the parameters - network id, broadcast address, and valid hosts.

 

[I am confused2]

Also, bare in mind that 129.33.112.x = IP address/range. A subnet is 255.xxx.xxx.xxx.

Their is a whealth of ip/subnet information on the web.

Here is a couple that will get you started.

IP address classes

https://learningnetwork.cisco.com/thread/21527

Google IP ADRESSING and then google subnetting. You will be over loaded with information.

 

[S0ULphIRE]

i dont know whether to treat that address as Class B type or a Class C type. If I knew this, I might be able to correctly align it for subnetting.

You can't go below /24 in a class C network, so your teacher must have meant class B.
Class C means XXX.XXX.XXX.000, where only the 000 part can be your host part. Anything below a /24 mask would mean you're cutting into the 3rd octet (because 3 sets of 8 bits = 24)

Again though, don't know why they're bothering to teach you classful addressing. It's useless now