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From: Marek Lindner <lindner_marek@yahoo.de>
To: Vasiliy Kulikov <segooon@gmail.com>,
        Linus =?utf-8?q?L=C3=BCssing?= <linus.luessing@web.de>
Subject: Re: batman-adv: design suggestions
Date: Sat, 14 Aug 2010 16:59:13 +0200
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Cc: "Greg Kroah-Hartman" <gregkh@suse.de>, Andrew Lunn <andrew@lunn.ch>,
        Sven Eckelmann <sven.eckelmann@gmx.de>,
        Simon Wunderlich <siwu@hrz.tu-chemnitz.de>, devel@driverdev.osuosl.org,
        linux-kernel@vger.kernel.org
References: <20100809203403.GA16183@albatros> <20100813181833.GA5632@albatros>
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On Friday 13 August 2010 20:18:33 Vasiliy Kulikov wrote:
> d) Why do you send icmp TTL exceeded for the icmp itself? E.g. in case
> of loop or/and small default TTL you'll probably get a storm of icmps.
> Exactly in this case IP silently drops TTL exceeded icmps ;)

These layer2 icmp packets are not ordinary icmp packets. We needed to provide 
a mechanism to make the network topology visible to debug tools like ping or 
traceroute which normally "see" no more than one hop as they operate on 
layer3. Hence, batman-adv does not send an icmp packet for each payload TTL 
exceeded but for traceroute only. I recommend reviewing the traceroute code to 
understand how this is supposed to work:
http://www.open-mesh.org/browser/trunk/batctl/traceroute.c

I'd be interested to learn about a problematic scenario in which this 
mechanism breaks.

Regards,
Marek
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