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"Programmers can't get IPv6 thus that is why they do not have IPv6 in their applications"....



On Fri, Nov 30, 2012 at 9:45 AM, Ray Soucy <rps at maine.edu> wrote:
> I'll see your disagree and raise you another ;-)
>
> I would say you almost never want to store addresses as character data
> unless the only thing you're using them for is logging (even then it's
> questionable).  I run into people who do this all the time and it's a
> nightmare.
>
> It's easy to store a v6 address as a string, but when you want to select a
> range of IPv6 addresses from a database, not having them represented as
> integers means you can't do efficient numerical comparisons in your SQL
> statements, it also makes indexing your table slower; to put it simply, it
> doesn't scale well.

Hi Ray,

If you've stored them in the string format I suggested, the string
comparison *is* an efficient numerical comparison. On a CISC processor
it may even be implemented with a single instruction byte string
comparison. Go test. You may be surprised at the results.

The one useful function you can't do directly from a string format is
apply an AND mask (netmask). More often than not this is irrelevant:
you don't want to load the data and then apply the mask, you want the
mask to constrain the data which you load from the database. You'd
need the database software to understand the address type and index it
with a radix tree, something it can do with neither a string format
nor your split 64-bit format.

In either case you substitute query by range for query by netmask.

WHERE IP>='A' AND IP<='B'

WHERE (IPHigh>AHigh AND IPHigh<BHigh) OR (IPHigh=AHigh AND
IPHigh!=BHigh IPLow>=ALow) OR (IPHigh!=AHigh AND IPHigh=BHigh AND
IPLow<=BLow) OR (IPHigh=AHigh AND IPHigh=BHigh AND IPLow>=ALow AND
IPLow<=BLow)

Which version looks more efficient to you?

Regards,
Bill Herrin


-- 
William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
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