Re: [patch] 2.4 version of my duplicate IP and MAC detection patch

From: Marc MERLIN (marc@merlins.org)
Date: Wed Sep 27 2000 - 22:15:15 EST


On Sat, Sep 23, 2000 at 02:02:24PM +0000, Julian Anastasov wrote:
> > I didn't receive any negative comments, except for Alexey who believed the
> > check should be done in user space.
>
> Now you receive another negative comment, for the 2.2 version :)
 
Thanks for the feedback, it is appreciated.
 
> Currently, in Linux 2.2 there is a device flag "hidden" which
> is based on this statement: many host can configure same IP address
> but it is assumed that only one is advertised. Your patch now will

Yes, I know LVS and arp_invisible, later renamed arp_hidden

> print messages for all these hidden addresses. They are not advertised
> and there is no problem caused from duplication.

I thought about that, but isn't the shared IP just an IP alias and not the
primary IP? As far as I know, the machines which share the IP have a primary
IP and put that one in their ARP packets, so my patch should not complain.

That said, adding a flag that lets you disable the duplicate IP detection on
an interface basis wouldn't be a bad idea, I'll look into this.

> - sip=127.0.0.0/8, this address is shared but we "assume" it is not
> advertised from the neighbours
 
Are you saying that some machines would ARP with a source IP of localhost?
That'd be pretty broken, wouldn't it? Or you talking about a kind of DOS
that would trigger warnings on all the machines?
(the dupe check could ignore that)
 
> - you work with ifa_address and not with ifa_local and ifa_mask.

I'll look into this too.

Thanks for your feedback.
Marc

-- 
Microsoft is to software what McDonalds is to gourmet cooking
 
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