From: "H. Peter Anvin" <hpa@zytor.com>
To: lkml@makubi.at
Cc: arndbergmann@googlemail.com, linux-kernel@vger.kernel.org
Subject: Re: DHCP and iptables
Date: Mon, 12 Oct 2009 15:45:58 -0700 [thread overview]
Message-ID: <4AD3B1A6.10508@zytor.com> (raw)
In-Reply-To: <20091012235013.16174ciovvwpw70g@www.kundendienste.net>
On 10/12/2009 02:50 PM, lkml@makubi.at wrote:
> Well, I just looked for "ethernet protocol" and read some things about
> DHCP again.
>
> What's an ethernet protocol?
>
> I also read, that "DHCP is built directly on UDP and IP" (RFC 2131).
>
> It uses Ports (UDP 67/68) and the source address of the DHCP server is
> an IP address.
>
> Could you answer me more in detail, why I get an IP, but block
> everything with iptables?
>
The reason is that the DHCP client bypasses the Linux IP stack
completely (because it has special requirements.)
> | | DHCP is an ethernet protocol, not an IP protocol, so you have to use
> | | ebtables instead of iptables to filter it.
> | |
> | | Arnd <><
This is actually incorrect -- DHCP is an IP (UDP, in fact) protocol. It
just has very special requirements (such as being able to use
src=0.0.0.0 dst=255.255.255.255) that aren't needed in normal operation,
so rather than slowing down the in-kernel IP stack it synthesizes raw
packets.
-hpa
next prev parent reply other threads:[~2009-10-12 22:46 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-12 21:50 DHCP and iptables lkml
2009-10-12 22:08 ` Arnd Bergmann
2009-10-12 22:41 ` lkml
2009-10-12 22:45 ` H. Peter Anvin [this message]
2009-10-12 22:53 ` lkml
2009-10-12 23:45 ` H. Peter Anvin
2009-10-12 23:59 ` Mathias Kub
-- strict thread matches above, loose matches on Subject: below --
2009-10-12 17:04 Mathias Kub
2009-10-12 16:34 lkml
2009-10-12 16:48 ` Arnd Bergmann
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