Subnetting

MJK9550

I am trying to get this stuff down, tell me if I am doing it correctly or if there is an easier/better way please.

192.168.10.0=Network
255.255.255.240/28=Mask

256-240=16
Subnets-0,16,32,48,64,80,96,112,128,144,160,176,192,208,224,240
Hosts per Subnet=14
Broadcast address- 15,31,47,63,79,95,111,127,143,159,175,191,207,223,239
Valid Hosts- 1-14, 17-30, 33-46, 49-62, 65-78, 81-94, 97-110, 113-126, 129-142, 145-158, 161-174, 177-190, 193-206, 209-222, 224-238

Am I missing anything?

Advice or tips much appreciated.

Cisco Inferno

Yes this is correct.

I would suggest this, with the mask of /28, just do 32-28=4. Then 2^4 = 16.

From there you have your block size. This magic number method is quite easier when starting out than remembering 240 etc. Those will come in time.


Just know your powers of 2, and learn to subtract from 32. super easy.

MJK9550

Okay thanks, so are there big difference in doing so for class b and class a subnets or is it just a matter or adding 0s basically.

Example: 255.255.240.0/28
subnets- 240=11110000=2^4=16?
hosts per subnet= ? 4 bits in the first octet and 8 in the second so 2^12-2=4094?
valid subnets= 0.0 - 16.0 - etc etc 0.255 - 16.255 - 32.255 etc etc ?

rob42

MJK9550 wrote: »

I am trying to get this stuff down, tell me if I am doing it correctly or if there is an easier/better way please. 192.168.10.0=Network 255.255.255.240/28=Mask 256-240=16 Subnets-0,16,32,48,64,80,96,112,128,144,160,176,192,208,224,240 Hosts per Subnet=14 Broadcast address- 15,31,47,63,79,95,111,127,143,159,175,191,207,223,239 Valid Hosts- 1-14, 17-30, 33-46, 49-62, 65-78, 81-94, 97-110, 113-126, 129-142, 145-158, 161-174, 177-190, 193-206, 209-222, 224-238 Am I missing anything? Advice or tips much appreciated.

A couple of things I’d like to comment on, if I may; using your example, you’d express the IP as 192.168.10.0/28 (CIDR notation), which means (as you know) “an IP address using a 28 bit Network Mask”. The mask 255.255.255.240 speaks for it’s self; it doesn’t need the /28. Also you’ve missed the 16^th Network (240) valid host rage and broadcast; 241-254: 255

james43026

You seem to have a good grasp on subnetting.

rob42

james43026 wrote: »

You seem to have a good grasp on subnetting.

Thank you very much! One day (I hope) I'll be ready to sit the CCNA exam (it's what I'm aiming at) and subnetting is (so I believe) a large part of that exam, so I'm pleased that you think I've a good grasp on the subject; it's comments such as yours that boost my confidence. Cheers buddy.