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Date:      Sun, 2 Sep 2001 02:30:27 +0100 (BST)
From:      Joshua Goodall <joshua@roughtrade.net>
To:        Paul Chvostek <paul@it.ca>
Cc:        <net@freebsd.org>
Subject:   Re: Gratuitous ARP (summary)
Message-ID:  <Pine.LNX.4.33.0109020130240.20276-100000@elm.phenome.org>
In-Reply-To: <20010901124938.A41615@gahch.it.ca>

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On Sat, 1 Sep 2001, Paul Chvostek wrote:

> FWIW, on aliased IPs, I seem to be unable to generate the who-has arps
> unless I specify the netmask.  Just doing "ifconfig if0 a.b.c.d alias"
> does not seem to be sufficient.  But the actual value of the netmask
> should not affect ARP, since ARP doesn't know about CIDR.

I see the same behaviour (as predicted by Ruslan). A full
ifconfig <interface> inet <address> netmask <mask> alias is required.

> I'd still like to know how to generate a gratuitous is-at.  I mean,
> besides forging it in dsniff's arpspoof.

I think the base system lacks the tools. You may be able to roll-your-own
with appropriate ioctls, this being all ifconfig does in practise.
However, none of them seem documented to perform any immediate ARP
functions, this being a side-effect of their functionality at best.

I think, ultimately, the only guaranteed way is to construct your own ARP
packet and write it at the link layer. arping uses libnet for this.

Joshua




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