From owner-freebsd-net@FreeBSD.ORG Thu Mar 15 00:16:16 2012 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 6E294106566C for ; Thu, 15 Mar 2012 00:16:16 +0000 (UTC) (envelope-from cswiger@mac.com) Received: from asmtpout028.mac.com (asmtpout028.mac.com [17.148.16.103]) by mx1.freebsd.org (Postfix) with ESMTP id 5390D8FC16 for ; Thu, 15 Mar 2012 00:16:16 +0000 (UTC) MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: text/plain; CHARSET=US-ASCII Received: from cswiger1.apple.com (unknown [17.209.4.71]) by asmtp028.mac.com (Oracle Communications Messaging Server 7u4-23.01 (7.0.4.23.0) 64bit (built Aug 10 2011)) with ESMTPSA id <0M0W006FWDYCAX40@asmtp028.mac.com> for freebsd-net@freebsd.org; Wed, 14 Mar 2012 16:15:49 -0700 (PDT) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.6.7498,1.0.260,0.0.0000 definitions=2012-03-14_06:2012-03-14, 2012-03-14, 1970-01-01 signatures=0 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 ipscore=0 suspectscore=0 phishscore=0 bulkscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=6.0.2-1012030000 definitions=main-1203140258 From: Chuck Swiger In-reply-to: <5E4F49720D0BAD499EE1F01232234BA87438162FAE@AVEXMB1.qlogic.org> Date: Wed, 14 Mar 2012 16:15:48 -0700 Message-id: References: <5E4F49720D0BAD499EE1F01232234BA87438162F95@AVEXMB1.qlogic.org> <1AB6F524-B4F4-4718-96C5-DB2951A02D59@mac.com> <5E4F49720D0BAD499EE1F01232234BA87438162FAE@AVEXMB1.qlogic.org> To: Adarsh Joshi X-Mailer: Apple Mail (2.1084) Cc: "freebsd-net@freebsd.org" Subject: Re: Zero MAC address X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 15 Mar 2012 00:16:16 -0000 On Mar 14, 2012, at 4:05 PM, Adarsh Joshi wrote: > Thank you for the quick replies. > > I am aware of the importance of the second bit. By invalid, I was wondering if that particular address is reserved or if it has any special meaning or purpose. There isn't a special meaning for all-zeros MAC to my knowledge, although all-ones MAC is subnet-local broadcast. > So in theory, I cannot classify it as an invalid MAC address on my packet statistics utility. Yes, as far as theory goes. In practice, all-zeros MACs tend to indicate that an ethernet driver failed to read the burned-in MAC assigned to the NIC. :-) > On a side thought, can an incoming packet be classified as "invalid MAC address" if it has the same MAC address of the host? Tentatively, yes-- MACs are supposed to be unique, and any collision is bad...just be careful that you aren't seeing packets which your local host had sent (perhaps because of a L2 switching loop). Regards, -- -Chuck