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From: Greg Smith <gsmith@gregsmith.com>
Cc: PostgreSQL Performance <pgsql-performance@postgresql.org>
Subject: Re: Best way to index IP data?
Date: Fri, 11 Jan 2008 21:56:38 -0500 (EST)
Message-ID: <Pine.GSO.4.64.0801112136430.23114@westnet.com> (raw)
In-Reply-To: <00045B34-A238-46B9-8641-C0A40C5CCCE5@blighty.com>
References: <36e682920801101541o7626bbddj428617144240c554@mail.gmail.com>
	<Pine.LNX.4.64.0801111025390.30762@localhost>
	<13179.1200064791@sss.pgh.pa.us>
	<20080111162747.GT5294@mathom.us>
	<24044.1200082058@sss.pgh.pa.us>
	<20080111212703.GU5294@mathom.us>
	<20080111213710.GD8260@alvh.no-ip.org>
	<20080111220235.GX5294@mathom.us>
	<20080111222403.GA7527@crankycanuck.ca>
	<1259C7B1-C948-4326-B827-849C64B61A16@blighty.com>
	<20080111230055.GB7618@crankycanuck.ca>
	<00045B34-A238-46B9-8641-C0A40C5CCCE5@blighty.com>

On Fri, 11 Jan 2008, Steve Atkins wrote:

> You may well need netmasks to configure your interface, but there's 
> absolutely no need for them to identify an IP endpoint, which is all you 
> need to identify the destination the packet is going to, and that is the 
> most common use of IP addresses.

Technically you can't ever send a packet unless you know both the endpoint 
and your local netmask.  As the sender, you're obligated to determine if 
the destination is on your local LAN (in which case you send it there) or 
if it goes to the gateway.  That's similar to a routing decision, but it's 
not quite--if you don't have to look in a routing table, it's not actually 
part of routing.

I believe this sort of detail is why subnet masks are considered required 
for some things even though it doesn't seem like they are needed. 
Regardless, the details of how the packets move aren't important to some 
applications, and arguing over what the RFCs do and don't require doesn't 
change that.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD



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