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Re: Very slow change of IP in kernel (slow socket?).

To: Andrea G Forte <andreaf@xxxxxxxxxxxxxxx>
Subject: Re: Very slow change of IP in kernel (slow socket?).
From: Martijn van Oosterhout <kleptog@xxxxxxxxx>
Date: Wed, 22 Dec 2004 17:26:32 +0100
Cc: netdev@xxxxxxxxxxx, linux-net@xxxxxxxxxxxxxxx
In-reply-to: <41C895D6.2040001@xxxxxxxxxxxxxxx>
References: <41C895D6.2040001@xxxxxxxxxxxxxxx>
Reply-to: Martijn van Oosterhout <kleptog@xxxxxxxxx>
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Seems long, but have you condered other possible delays, like ARP,
routing daemons, etc. BTW, I don't quite understand what you mean by
changing IPs, because "ip route add" adds routes, not IPs. Presumably
you're using an unbound UDP socket. You need to be a bit clearer about
what you're actually trying to do...

On Tue, Dec 21, 2004 at 04:29:58PM -0500, Andrea G Forte wrote:
> Hi all,
> after some talking I decided to try again and post a specific thread for 
> this problem.
> I noticed that when I change IP address for the same wireless card 
> (since I am moving to a different subnet I need a new IP), the actual 
> change in the kernel happens between 300 to 500 ms later. In particular, 
> after changing the IP (ip route add...) and updating route table and 
> default gw, the actual data packets are sent using the new IP only after 
> 300 to 500 ms after setting all the above.
> Does anyone of you know what this could be related to? Or, does anyone 
> of you know where in the kernel code I could start looking for some answers?
> I have already had some feedback with suggestions to look into the 
> route_cache, however this does not seem to me as a route problem but 
> more as a socket problem and perhaps some kind of timer that is set to 
> refresh the socket info in the kernel.
> Any help would be really appreciated.
> Thanks all,
> Andrea
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Martijn van Oosterhout   <kleptog@xxxxxxxxx>
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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