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Re: Lookup zip by IP address [message #172975 is a reply to message #172974] Mon, 14 March 2011 13:54 Go to previous messageGo to previous message
The Natural Philosoph is currently offline  The Natural Philosoph
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Registered: September 2010
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Roy Smith wrote:
> In article <9iurn6pkg5iifq39ii9isstrqb7f8ncc95(at)mfesser(dot)de>,
> Michael Fesser <netizen(at)gmx(dot)de> wrote:
>
>> .oO(D. Stussy)
>>
>>> "Jerry Stuckle" <jstucklex(at)attglobal(dot)net> wrote in message
>>> news:ileocv$pkg$1(at)news(dot)eternal-september(dot)org...
>>>> IP addresses can change as often as every transmission, or as seldom as
>>>> almost never. They are not reliable.
>>> Every transmission: No.
>>> Every SESSION: Yes.
>>>
>>> One cannot have TCP sessions when it changes every transmission.
>> Every single request may come from a different IP address. Sessions have
>> nothing to do with TCP and are not bound to a particular IP address.
>
> The concept of "session" (in the context of the ISO 7-layer model) is
> somewhat vaguely defined, but in general I would agree with this
> statement.
>
> Most web applications maintain some state in a browser cookie which they
> use to establish session continuity across multiple HTTP requests. Each
> of those HTTP requests uses a new TCP connection.

Not always, as I understand it.

http://en.wikipedia.org/wiki/HTTP_persistent_connection

However, such connections time out fairly quickly. So if you take more
than a couple of minutes to read - say - a page before moving on, you
get a new connection.

I think the idea is that when you hit a site with - say - a load of
images and css files you use just one connection to pull the lot down,
rather than multiple ones.

Thus preventing massive spawning of parallel processes at the far end.

But that's guesswork.


> On a host with
> multiple interfaces (or a mobile host),

Or a DHCP client that goes 'off line' briefly..

> each of those TCP connections
> could come from a different IP address.
>
> Since HTTP sits on top of TCP, there is some logic to calling HTTP the
> ISO session layer, but that's a bit warped. Certainly, the maintaining
> of web application sessions via browser cookies is not something which
> is part of HTTP itself. If you were to try to crowbar it into the ISO
> model, it would really fall into some higher level, but such attempts
> are usually futile.
>
> As for the statement, "IP addresses can change as often as every
> transmission", it's hard to say whether that's correct or not without
> knowing how you're defining "transmission". If by "transmission", you
> mean "HTTP request", then yes, it's correct. If you mean "TCP packet",
> then no, it's not correct. If you mean something else, then I have no
> idea if it's correct or not until I know what that something else is :-)

I think that's pretty clear. :-)
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