blocking dhcp on bridge

Ron Peterson rpeterso at
Mon Feb 14 23:09:13 CET 2005

On Mon, Feb 07, 2005 at 01:57:11PM -0500, Ron Peterson wrote:
> On Sun, Feb 06, 2005 at 04:01:54PM -0500, Ron Peterson wrote:
> > I am running a dhcp server on a bridging firewall.  The dhcp server runs
> > on br0.  I have eth0 connected to my 'private' network, and eth1
> > connected to my 'public' network.
> > 
> > I only want this dhcp server to service dhcp requests from the private
> > network.  Any dhcp requests entering via eth1, or any dhcp replies being
> > sent via eth1 should be dropped.

I stopped using iptables, and used ebtables instead.  Seems to work.

Obviously, there is some overlapping functionality between these two
toolsets.  I'm learning the hard way when to use which tool.

$EBTABLES -A INPUT --in-interface $PUB --protocol IPv4 --ip-protocol udp --ip-source-port 68 -j DROP
$EBTABLES -A INPUT --in-interface $PUB --protocol IPv4 --ip-protocol udp --ip-destination-port 67 -j DROP
$EBTABLES -A FORWARD --in-interface $PRIV --protocol IPv4 --ip-protocol udp --ip-source-port 68 -j DROP
$EBTABLES -A FORWARD --in-interface $PUB --protocol IPv4 --ip-protocol udp --ip-destination-port 67 -j DROP

Ron Peterson
Network & Systems Manager
Mount Holyoke College

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