netdev - Re: [RFC PATCH] dont create cached routes from ARP requests

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Message-ID: <4C9CC608.7010401@astaro.com>
Date:	Fri, 24 Sep 2010 17:38:48 +0200
From:	Ulrich Weber <uweber@...aro.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Ulrich Weber <ulrich.weber@...glemail.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [RFC PATCH] dont create cached routes from ARP requests

Yes, as I wrote before my Cable ISP is flooding me with
ARP requests from 10.0.0.0/8, which get a route
via the primary PPP link.

I know thats not a common setup but why do that
kind of routes have to be cached ? :)


steps to reproduce:
server:
 ip route add 1.0.0.0/8 dev dummy0

client:
 ip route add 1.0.0.0/8 dev eth0
 nmap --min-rate 500 -sP 1.0.0.0/8


On 09/24/2010 05:28 PM, Eric Dumazet wrote:
> Le vendredi 24 septembre 2010 à 17:00 +0200, Ulrich Weber a écrit :
>> Hi Eric,
>>
>> please find the output in the attached text file.
>>
>> Neighbor garbage collection wont't work because all
>> neighbor records are bound to cached routes.
>>
>> Forced route garbaged collections returns without freeing
>> any routes, probably because the route threshold is quite high
>> with 65536 compared to the small neighbor threshold of 1024,
>> resulting in a fixed amount of 1024 cached routes...
>>
>> Instead of running the garbage collection we could flush the route
>> cache completely if the neighbor cache overflows.
>> But why do we have to cache that routes in first place ?
>> See the previous patch which skips caching for that kind of routes.
> 
> What are the packets you receive ? A flood of ARP answers ?
> 
> a "tcpdump -X" of a few packets would help to understand.
> 
> 
> 


-- 
Ulrich Weber | uweber@...aro.com | Software Engineer
Astaro GmbH & Co. KG | www.astaro.com | Phone +49-721-25516-0 | Fax –200
An der RaumFabrik 33a | 76227 Karlsruhe | Germany
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