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Date:      Wed, 24 Jan 2001 00:30:24 -0500
From:      "C. Stephen Gunn" <csg@waterspout.com>
To:        Julian Elischer <julian@elischer.org>
Cc:        Patrick Bihan-Faou <patrick@netzuno.com>, Mitch Collinsworth <mitch@ccmr.cornell.edu>, freebsd-net@FreeBSD.ORG
Subject:   Re: How to send arp request with no other traffic
Message-ID:  <20010124003024.A231@waterspout.com>
In-Reply-To: <3A6E1499.D9578008@elischer.org>; from julian@elischer.org on Tue, Jan 23, 2001 at 03:32:41PM -0800
References:  <HJEEKLMFLKEOKHOKNPBMKEDBCJAA.patrick@netzuno.com> <3A6E1499.D9578008@elischer.org>

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On Tue, Jan 23, 2001 at 03:32:41PM -0800, Julian Elischer wrote:

> send a hand crafted arp packet out through the nergraph
> hook on the interface and let the response be put in the table.

This is a side-effect of the ARP packet processing mechanism
described in STD-0037.  All inbound ARP packets are processed and
inserted into the kernel table, before checking if a response is
solicited or appropriate.  The intention of the original designers
of ARP was to use this mechanism to minimize the need for broadcasts
on the network.

I bring this up to say this is only a valid assumption on the ARP
implementation in FreeBSD.  I have not compared the STD-0037
recommendations with the implementation in NetBSD, and I am fairly
certain that Linux _DOES_NOT_ note arp-updates from unsolicited
packets.  <sigh>

Sending spoofed ARP requests from the host in question will also
require root, which inspecting the kernel routing and arp table
currently doesn't. 

 - Steve

--
C. Stephen Gunn <csg@waterspout.com>   |   Waterspout Communications, Inc.


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