11-26-2008 12:55 PM - edited 03-04-2019 12:30 AM
Okay,
How do I get the subnet ID if I have an address and mask only?
I always use a calculator (Advanced IP Address Calculator is good), but I've been trying to figure this out.
172.20.13.27 255.255.255.240
I *know* what the subnet id is (the beginning of the block), but how would I figure this out quickly?
Thanks,
John
Solved! Go to Solution.
11-26-2008 01:07 PM
John
256 - 240 (240 because of the last octet in 255.255.255.240) = 16 so subnets go up in 16
172.20.13.0
172.20.13.16
172.20.13.32
so subnet is 172.20.13.16
Jon
11-26-2008 01:11 PM
Hello John,
make the conversion in binary of ip address and subnet mask
let's concentrate on 4th byte
27 = 00011011 binary
240 = 11110000 binary
then you put zeros in the host position of the mask
that leave you:
16 = 10000 binary
so the subnet address is:
172.20.13.16/28
Hope to help
Giuseppe
11-26-2008 01:07 PM
John
256 - 240 (240 because of the last octet in 255.255.255.240) = 16 so subnets go up in 16
172.20.13.0
172.20.13.16
172.20.13.32
so subnet is 172.20.13.16
Jon
11-26-2008 01:11 PM
Hello John,
make the conversion in binary of ip address and subnet mask
let's concentrate on 4th byte
27 = 00011011 binary
240 = 11110000 binary
then you put zeros in the host position of the mask
that leave you:
16 = 10000 binary
so the subnet address is:
172.20.13.16/28
Hope to help
Giuseppe
11-26-2008 01:14 PM
Giuseppe, he said quickly :-)
11-26-2008 01:19 PM
hello Jon,
I was going to edit my post ...
because of course John is not so a beginner to need a full binary lesson !
Excuse me John !
Best Regards
Giuseppe
11-26-2008 01:23 PM
Giuseppe
I was just making a joke, no offense intended at all. The joke being that converting backwards and forwards from binary is not that quick ! or at least it isn't for me.
Once again no offense intended.
Jon
11-26-2008 01:43 PM
Hello Jon,
I understood your joke -))
no offense at all
Best Regards
Giuseppe
11-26-2008 02:55 PM
Thanks Jon and Giuseppe! Yeah, after I had posted this I decided to write it out in binary and I got the same thing. Jon I seem to remember asking you this a couple of weeks ago though. Sorry if this is the same exact question! :-)
Thanks!
John
11-26-2008 03:01 PM
Hello all,
I normally follow a mixture of both procedures to find subnets or things like that, depending on what fits me best at a particular time. The binary might not be quick for some people, but for me it's good when I am too tired to think of shortcuts. I think binary is a definite method, unless one really hates binary.
Always nice to see people having fun here :-)
Kind Regards,
M.
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