netdev - Re: [iproute PATCH] iproute: restrict hoplimit values to be in range [1;255]

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Date:	Mon, 23 Nov 2015 15:48:44 -0800
From:	Stephen Hemminger <shemming@...cade.com>
To:	Phil Sutter <phil@....cc>
CC:	<netdev@...r.kernel.org>
Subject: Re: [iproute PATCH] iproute: restrict hoplimit values to be in
 range [1;255]

On Tue, 10 Nov 2015 13:54:09 +0100
Phil Sutter <phil@....cc> wrote:

> Technically, the range of possible hoplimit values are defined by IPv4
> and IPv6 header formats. Both define the field to be eight bits in size,
> which leads to a value range of [0;255]. Setting a packet's hoplimit
> field to 0 though makes not much sense, as the next hop would
> immediately drop the packet. Therefore Linux uses 0 as a special value
> indicating to use the system's default hoplimit (configurable via
> sysctl). In iproute, setting the hoplimit of a route to 0 is equivalent
> to omitting the hoplimit parameter alltogether, so it is not necessary
> to allow that value to be specified.
> 
> Signed-off-by: Phil Sutter <phil@....cc>

Even though it doesn't make much sense to set hoplimit of 0;
I am concerned that some user is doing that now, and changing this
would break a working (but not optimum or sane) configuration.
Especially if actual config is auto-generated.
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