| From: | Thom Brown <thom(at)linux(dot)com> |
|---|---|
| To: | Zhidong <zhidong(dot)she(at)gmail(dot)com> |
| Cc: | Ondrej Ivanič <ondrej(dot)ivanic(at)gmail(dot)com>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: IP range in pg_hba.conf? |
| Date: | 2011-11-08 13:44:15 |
| Message-ID: | CAA-aLv6ZYPOTbgqZugmPk1oZj_AWdf+-3sLr8krDnZJX3QdzFg@mail.gmail.com |
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| Lists: | pgsql-general |
2011/11/8 Zhidong <zhidong(dot)she(at)gmail(dot)com>:
> Can you guys explain why it is 10.17.64.0/20? Thanks!
11111111 = 255 in binary
11110000 = 240 in binary
So a CIDR mask of 8 would cover the first 8 bits, 16 the next 8, but
when we reach 20 we've covered 20 bits.
The first 255 is the first 8 bits. The next 255 is bits 9-16. Bits
17-20 brings it up to 240. The rest are zeros.
0.0.0.0 = /0
255.0.0.0 = /8
255.255.0.0 = /16
255.255.255.0 = /24
255.255.255.255 = /32
And inbetween you get:
255.255.240.0 = /20
255 255 240 0
11111111 11111111 11110000 00000000
First 20 binary digits are masked.
--
Thom Brown
Twitter: @darkixion
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