Re: DHCP and iptables

[lkml]

> On 10/12/2009 02:50 PM, lkml@xxxxxxxxx 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

So iptables uses the in-kernel IP stack and because of that fact, it  
is not able to filter the DHCP packets?

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