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


On Thu, 21 Sep 2000, Marc MERLIN 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 :)

You claim that it is not possible two hosts to configure same IP
address. Why? The problem is when this IP address is advertised
using ARP not when it is configured.

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

May be you can add device flag that will allow these messages
to be printed and the problem detected.

So, the lookup for the local address depends on many
conditions. May be not all of them can be accessed from user space
but the current kernel implementation must be corrected. I agree with
you that for the user implementation it will be very difficult to
detect which address is local considering the advanced routing rules.
I have never tried such lookups from user space yet.

Other problems:

- sip=, this address is shared but we "assume" it is not
advertised from the neighbours

- you work with ifa_address and not with ifa_local and ifa_mask.


Julian Anastasov <>

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