From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Re: ARP problem? Date: Wed, 16 Oct 2002 16:06:51 -0700 Sender: netdev-bounce@oss.sgi.com Message-ID: <3DADF10B.3080804@candelatech.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: "'netdev@oss.sgi.com'" Return-path: To: "Thompson, Ian" Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Thompson, Ian wrote: > Hi, > > I'm seeing some odd behavior in RedHat 7.3 when handling ARP packets. I > have two Intel NIC cards, eth0 and eth1, in one machine, connected to the > same switch. eth0 is set to IP0 and has MAC addr M0, and eth1 is at IP1 and > MAC M1. Now, if another machine connected to the switch sends an ARP > broadcast asking who is at IP0, I see two replies on the wire -- IP0 is at > M0, and IP0 is at M1. This result seems contradictory to me; could it be > some sort of feature that I'm not aware of? If so, can I disable it? > > I am trying to devlop some code to support an active failover case, so I > want two seperate devices on the same physical network. I have seen the > same result even if IP0 and IP1 are on different subnets, or even if one is > a class A and the other is a class C address. > > I'm sorry if this has already been discussed -- I haven't seen much relating > to it in the archives. You need arp-filtering: # Set up arp-filter magic. This, with source-based routing allows us # to have multiple NICs on the same subnet, on the same machine, connected # to the same switch... if [ -f /proc/sys/net/ipv4/conf/all/arp_filter ]; then echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter else echo "ERROR: kernel does not support arp_filter. Don't put more than" echo " one interface on the same subnet on the same machine." echo "" fi > > TIA, > -ian > > --- > Ian Thompson Firmware Engineer > Adaptec, Inc Storage Networking Group > 408.957.4909 408.957.6800 (fax) > ian_thompson@adaptec.com > > -- Ben Greear President of Candela Technologies Inc http://www.candelatech.com ScryMUD: http://scry.wanfear.com http://scry.wanfear.com/~greear