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From: Robert Hajime Lanning <lanning@lanning.cc> Subject: Re: [svlug] eth and BROADCAST flag To: dcopeland@linuxfan.com (Dan Copeland) Date: Tue, 26 Sep 2000 13:46:45 -0700 (PDT) Cc: svlug@svlug.org Dan Copeland wrote: > I have a Red Hat 6.1 machine which I use as a NAT box > for my DSL connection with ipchains packet filtering. > Obviously it has two physical network interfaces, one > facing my DSL provider and one facing my internal network, > which consists of 10.* addresses. > > I came across the following in the process of learning > ISC dhcpd, which I want to install on the firewall > machine: > > "If no interface names are specified on the command line dhcpd will > identify all network interfaces which are up, elimininating non-broadcast > interfaces if possible, and listen for DHCP broadcasts on each interface." > > My out-facing interface is not non-broadcast (that is, > it has the BROADCAST flag and a broadcast address set). > > 1) Should this interface be non-broadcast? What effect > does this have? Obviously I don't want dhcpd listening to > this interface - it this the correct way to accomplish > that? > > 2) If so, how do I make the interface persistently > non-broadcast (i.e. over a reboot)? It seems there > should be an option in > /etc/sysconfig/network-scripts/ifcfg-eth0. Is there one I > can add? > > Many thanks from a pseudo-newbie and long time lurker. You don't want to turn off BROADCAST on any of the ethernet interfaces. No one will be able to ARP the interface. Just tell dhcpd specificaly which interfaces to bind to. I do this on my machine at work. I have a private network in my cubicle with dhcp on it. So I start dhcpd with the command "dhcpd eth1". (eth0 is the company network)