Re: [PATCH] net/ipv4/arp.c: Fix arp reply when sender ip 0 (was: Strange behavior in arp probe reply, bug or feature?)

Alexey Kuznetsov
2007-11-19T13:06:27Z

Hello!

> Is there a reason that the target hardware address isn't the target
> hardware address?

It is bound only to the fact that linux uses protocol address
of the machine, which responds. It would be highly confusing
(more than confusing :-)), if we used our protocol address and hardware
address of requestor.

But if you use zero protocol address as source, you really can use
any hw address.

> The dhcp clients I examined, and the implementation of the arpcheck
> that I use will compare the target hardware field of the arp-reply and
> match it against its own mac, to verify the reply. And this fails with
> the current implementation in the kernel.

1. Do not do this. Mainly, because you already know that this does not work
with linux. :-) Logically, target hw address in arp reply is just
a nonsensial redundancy, it should not be checked and even looked at.

2. What's about your suggestion, I thought about this and I am going to agree.

Arguments, which convinced me are:

- arping still works.
- any piece of reasonable software should work.
- if Windows understands DaD (is it really true? I cannot believe)
and it is unhappy about our responce and does not block use
of duplicate address only due to this, we _must_ accomodate ASAP.
- if we do,we have to use 0 protocol address, no choice.

Alexey