netdev - Re: [PATCH 2/2] ipv4: flush ARP entries on device change

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Date:	Wed, 03 Mar 2010 16:39:36 +0200
From:	Timo Teräs <timo.teras@....fi>
To:	Patrick McHardy <kaber@...sh.net>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] ipv4: flush ARP entries on device change

Patrick McHardy wrote:
> Timo Teräs wrote:
>> Patrick McHardy wrote:
>>> Timo Teras wrote:
>>> It would be nice if we could restrict this to IFF_NOARP changes.
>> Yes. But I did not see any easy way to figure out which flags have changed.
>>
>> Should we just keep a copy of the previous IFF_NOARP bit somewhere
>> (where?).
>> Or did I miss something obvious?
> 
> We shouldn't have any arp entries for devices with IFF_NOARP set,
> so perhaps we can flush only in that case. The transition IFF_NOARP
> -> ~IFF_NOARP shouldn't need flushing.

IFF_NOARP devices do have neighbor entries with the nud NOARP.
Exactly those entries I want to flush when IFF_NOARP flag is
removed.

You can see those entries with "ip neigh show nud all". You have
them e.g. for loopback stuff and broad-/multicast stuff in general.
With IFF_NOARP you get them on all unicast addresses used.

- Timo
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