From mboxrd@z Thu Jan  1 00:00:00 1970
From: Brian Haley <brian.haley@hp.com>
Subject: Re: [PATCH] ipv4/ipv6: check hop limit field on input
Date: Mon, 01 Jun 2009 14:55:20 -0400
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References: <4A23F027.3060907@dev.6wind.com> <20090601161917.GA29745@Chamillionaire.breakpoint.cc> <4A240681.2010300@6wind.com> <4A242161.3010609@cosmosbay.com>
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Cc: nicolas.dichtel@6wind.com, Florian Westphal <fw@strlen.de>,
	netdev <netdev@vger.kernel.org>
To: Eric Dumazet <dada1@cosmosbay.com>
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Eric Dumazet wrote:
> Nicolas Dichtel a =E9crit :
>> Le 01.06.2009 18:19, Florian Westphal a =E9crit :
>>> Nicolas Dichtel <nicolas.dichtel@dev.6wind.com> wrote:
>>>> when network stack receives a packet, it didn't check value of
>>>> ttl/hop limit
>>>> field. RFC indicates that a router must drop the packet if this fi=
eld
>>>> is 0.
>>> Whats wrong with the checks in ip(6)_forward?
>> It's on forward, not on input. Router must not process it.
>> For example, if you try to ping (with ttl set to 0) the router, you =
will
>> receive a reply.
>>
>=20
> You seem to mix requirements for routers and hosts. ttl processing
> is relevant for a gateway only, not for a host.
>=20
> (terminology : gateway / host in rfc 792)
>=20
> I would say : who sent this ttl=3D0 packet at first ?
>=20
> ping -t 0 host
> ping: can't set unicast time-to-live: Invalid argument
>=20
> So Linux is not able to do that, unless using tricks of course, or pa=
tching IP_TTL

'ping6 -t 0 host' does work however.  The problem I see is that if you =
ping a system,
if it's a host it will respond, if it's a router it won't - the RFCs do=
n't
explicitly state the host should drop the packet.  I don't know if that=
 difference
in behavior is desired.  Do we know how any other OSes behave?

-Brian