From: Ulisses <ra993482@ic.unicamp.br>
To: Kohei OHTA <kohei@cysols.com>
Cc: netdev@oss.sgi.com
Subject: Re: IP-ID field of ICMP echo request
Date: 07 Jul 2003 15:40:36 -0300 [thread overview]
Message-ID: <1057603237.1001.18.camel@ryback> (raw)
In-Reply-To: <3F095B7B.5090203@cysols.com>
On Mon, 2003-07-07 at 08:37, Kohei OHTA wrote:
> I found a strange packet, which is generated by ping of Linux.
> It is observed ID field of IP header in ping packet (Echo request) is always 0.
>
> I confirmed this on kernel 2.4.18 and 2.4.21.
> My colleague also confirmed this is fixed in kernel 2.5.74.
>
> I hope this is fixed in next next 2.4.x release.
Hi, Kohei,
I guess this behaviour is to prevent Idle scanning, that is based on
predictable IPID numbers [1]. Therefore, the Linux TCP/IP stack uses 0
as IPID when the DF (Don't Fragment) bit is set. I'm not sure, but I
think that Linux also uses peer-specific IPID numbers to make the
prediction harder.
-- Ulisses
[1] http://www.insecure.org/nmap/idlescan.html
next prev parent reply other threads:[~2003-07-07 18:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-07-07 11:37 IP-ID field of ICMP echo request Kohei OHTA
2003-07-07 12:29 ` Maciej Soltysiak
2003-07-07 12:39 ` YOSHIFUJI Hideaki / 吉藤英明
2003-07-07 12:48 ` Maciej Soltysiak
2003-07-07 13:11 ` YOSHIFUJI Hideaki / 吉藤英明
2003-07-07 18:40 ` Ulisses [this message]
2003-07-08 1:59 ` Kohei OHTA
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