forwarding with ttl=1

Dancho Penev dpenev at
Thu Feb 5 12:05:23 PST 2004

On Thu, Feb 05, 2004 at 03:17:04PM +0200, Alexander Botov wrote:
>From: "Alexander Botov" <alexb at>
>To: <freebsd-questions at>
>Date: Thu, 5 Feb 2004 15:17:04 +0200
>Subject: forwarding with ttl=1
>Hi All 
>I am newbie with configuring networks under FreeBSD . I have small network with gateway running on FreeBSD 5.2 Release .My ISP offers me pppoe service for connecting to Internet . I didn't have problems with configuring ppp with pppoe . I used nat option wchich works fine for masquerading the local network from the world . The problem is that the ISP's gateway returns every time packets with ttl=1 which makes further forwarding impossible . My gateway returns icmp error mesage "time exceeded" and discards packets . I want to know if I made some mistake with configuring nat service or if not what is the solution of the problem ? Is there any service that can increment ttl and process the packet ? I tried to avoid the checking of ttl in the ip_forward() function in ip_input.c and skipping the decrement of ttl and everything works fine but i think that this is very ugly kernel hack . Probably there is an easy and elegant solution . Any ideas ?

You don't need to hack the kernel because this was already did.

options		IPSTEALTH

in your kernel configuration file, build the new kernel and
set net.inet.ip.ipstealt sysctl variable to 1.
For more information see /usr/src/sys/conf/NOTES and

>please excuse my English
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Dancho Penev

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