From: Henrik Nordstrom <hno@marasystems.com>
To: cranium2003 <cranium2003@yahoo.com>
Cc: kernelnewbies@nl.linux.org, netdev@oss.sgi.com,
netfilter-devel@lists.netfilter.org,
linux-kernel@vger.kernel.org
Subject: Re: netfilter query
Date: Mon, 22 Nov 2004 13:03:23 +0100 (CET) [thread overview]
Message-ID: <Pine.LNX.4.61.0411221245470.20973@filer.marasystems.com> (raw)
In-Reply-To: <20041121153354.99557.qmail@web41404.mail.yahoo.com>
On Sun, 21 Nov 2004, cranium2003 wrote:
> Also,which headers are added when packet
> reaches to netfilter hook NF_IP_LOCAL_OUT? I found
> TCP/UDP/ICMP ,IP. Is that correct?
Yes.
netfilter is running at the IP layer and only reliably have access to IP
headers and up. Lower level headers such as Ethernet MAC header is
transport dependent and not always available, and certainly not available
in NF_IP_LOCAL_OUT as it is not yet known the packet will be sent to an
Ethernet.
In some netfilter hooks it is possible to rewind back to the Ethernet MAC
header but one must be careful to verify that it really is an Ethernet
packet one is looking at when doing this. Unfortunately there is no
perfect solution how to detect this.. For an example of how one may try to
look at the Ethernet MAC header see ipt_mac.c. But be warned that it is
possible for non-Ethernet frames to pass the simple checks done there..
Regards
Henrik
next prev parent reply other threads:[~2004-11-22 12:04 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-11-21 15:33 cranium2003
2004-11-22 12:03 ` Henrik Nordstrom [this message]
2004-11-23 1:47 ` Stuart Macdonald
2004-11-23 6:00 ` cranium2003
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Pine.LNX.4.61.0411221245470.20973@filer.marasystems.com \
--to=hno@marasystems.com \
--cc=cranium2003@yahoo.com \
--cc=kernelnewbies@nl.linux.org \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@oss.sgi.com \
--cc=netfilter-devel@lists.netfilter.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®