IP address range matching

[Thantos]

Running into this at work. I have IP address ranges like 209.85.128.0/17 and I'm trying to figure out how that matches 209.85.217.221

I thought the 0/17 only affected the last octet but it appears I'm wrong (via other documents) but even then I can't see how the 3rd octet matches.

Any one have some references they could point me to?

[tabstop]

The /17 means that only the first seventeen bits are used for the subnet mask -- which means, in the third octet, only the first byte must be matched. Your subnet goes from 209.85.128.0 to 209.85.255.255.

You can probably google "subnetting calculator" or something like that.

(Edit: first byte!?! first bit. Sorry.)

[Thantos]

Got to love how just a little bit more searching after asking finds you the solution

Turns out the IP is in CIDR notation - Wikipedia, the free encyclopedia where the /17 specifies the subnet mask.