Comments on: Do subnet math in your head

By: Steven

Steven — Sun, 20 Mar 2011 22:16:11 +0000

Found this really useful so thanks!

By: Gregg

Gregg — Wed, 10 Nov 2010 08:08:40 +0000

Quiz – for subnet masking – http://mochabomb.com/main/node/262
I’ll add more questions in time..

By: arnie

arnie — Fri, 11 Jun 2010 04:08:00 +0000

great, very clear, better than my cisco class teacher

By: gregg

gregg — Sat, 24 Apr 2010 05:58:13 +0000

Thanks – fixed – and some other edits also.

By: John

John — Fri, 23 Apr 2010 18:57:19 +0000

This is a great site, thanks for taking the time to post this.

I think there is one error:

Summary:
8 addresses: First is network, 6 in the middle for hosts, last is the broadcast address:

192.168.1.16 network
192.168.1.17 to 192.168.0.22 hosts
192.168.1.23 broadcast
255.255.255.248 subnet mask

Shouldn’t it be:

192.168.1.17 to 192.168.1.22 hosts
^

Thx!

By: Yogesh

Yogesh — Wed, 07 Oct 2009 04:47:54 +0000

thanks bro……..
it is very good calculation from you.
i was trying last one month but your post helped me. keep it on.

By: gregg

gregg — Wed, 29 Jul 2009 05:55:31 +0000

subnet mask – 23 bits – 255.255.254.0, /23 netmask on all parts of the network. Note there will be issues only crossing boundaries – an old machine with /24 netmask I expect will not see machine on 192.168.2.0 – without going through the router. The packet will arrive – can be funky and depend I think on the switch, but need to really verify this…

By: Jude

Jude — Tue, 28 Jul 2009 05:58:40 +0000

My network was initially 192.168.1.0 but i have more than 250 hosts and now my DHCP server has given me the network 192.168.2.0 of which my new hosts cant recieve HTTP information , what do i do

By: Richard Ward

Richard Ward — Sun, 07 Jun 2009 23:12:49 +0000

Dude.. Thanks! I am going to take my CCNA in about two more weeks. I have been taking network related classes for the past 2.5 years. We went over all of this in the very beginning but I never really got a firm grasp on it. This should help – GREATLY!

By: gregg

gregg — Thu, 13 Nov 2008 01:36:42 +0000

.. great idea – I’ll start working on it and that has a good question – please feel free to contribute suggestions.

By: emmanuel

emmanuel — Wed, 12 Nov 2008 14:11:20 +0000

could we also get some online objective questions after which an evaluation score is given. thanx.

By: jon

jon — Thu, 16 Oct 2008 23:32:19 +0000

nice……
this helped me to understand. just starting out.

just like the mult.table, this is now in my back pocket!

By: aq

aq — Tue, 07 Oct 2008 00:35:00 +0000

I like this. This site is far easier than other sites, once you get past the binary numbers.

By: gregg

gregg — Fri, 05 Sep 2008 01:12:27 +0000

Fixed – thanks for stopping by and the comment!

By: Ran

Ran — Thu, 04 Sep 2008 11:13:21 +0000

I noticed a minor error in your calculation that may confuse some folks while perusing your web site…

How to easily remember this:
Mentally I think this: I see 192.168.1/24 – then
1. an IP address has 32 bits for address
2. 32 – 24 = 4; 2^8 = 256;
3. 256 addresses – first one is network; last one is broadcast, the rest in the middle are hosts.

#2. 32 – 24 = 8…not 4