4 Replies Latest reply: Mar 27, 2018 5:42 PM by ciscodaze1 RSS

    Subnetting question

    Danny

      Hi guys,

      I have a subnetting question that hope you can help me with. The question is the following:

       

      I am given IP address 192.168.15.30 and subnet mask 255.255.255.252 and I need to find out what is the subnet id for this IP.

       

      Before anything else, I'd like to explain that the method I am using for practising subnetting (and which I am pretty comfortable with) focuses on the use of 8, 16 and 32 values to find out what the increments are for the subnets.

       

      In this example, 255.255.255.252 is /30 in CIDR notation. This means that my increment would be 2^ (32-30) = 2^2= 4.

       

      Based on that increment, I would list the network ranges (adding the increment on the last octet) as follows:

       

      192.168.15.0

       

      192.168.15.4

       

      192.168.15.8

       

      ..................

       

      192.168.15.224

       

      192.168.15.228 (192.168.15.231)

       

      192.168.15.232

       

      Based on my results, the subnet id for 192.168.15.30 would be 192.168.15.228.

       

      I see this method very easy to understand and to implement to get fast results in most of the examples. However, in a case like this example (where you have to increment all the way from 0 to 228) is not fast enough for me). I tried to say "ok, 4 times 50 is 200, 4 times 60 is 240 so my subnet is somewhere around those limits". From there, I keep looking for the right multiple of 4 to get to my value between 50 and 60.

       

      This makes me spend a lot of time in trying to find this number.

       

      In order to get accurate at subnetting with this method, I have learned by heart the mutliples for 128, 64,32 and 16 up to 256 (well, really easy for 128 as there's only 0 and 128) but for increments with values 8,4 and 2 I struggle when the increment for the subnet is far away from 0.

       

      Do you guys have any method or technique that might help for these types of scenarios?

       

      Thanks all in advance.

       

      Regards,

       

      Daniel