From owner-freebsd-current Sun May 7 19:40:30 2000 Delivered-To: freebsd-current@freebsd.org Received: from yellow.rahul.net (yellow.rahul.net [192.160.13.18]) by hub.freebsd.org (Postfix) with ESMTP id E13CF37BC04 for ; Sun, 7 May 2000 19:40:27 -0700 (PDT) (envelope-from dhesi@rahul.net) Received: by yellow.rahul.net (Postfix, from userid 104) id 961B97C37; Sun, 7 May 2000 19:40:27 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by yellow.rahul.net (Postfix) with ESMTP id 8BEBF7C36; Sun, 7 May 2000 19:40:27 -0700 (PDT) Date: Sun, 7 May 2000 19:40:27 -0700 (PDT) From: Rahul Dhesi To: Bill Fenner Cc: freebsd-current@freebsd.org Subject: Re: gratuituous arp for multiple IP addresses In-Reply-To: <200005080230.TAA09785@windsor.research.att.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Ok, I stand corrected. Rahul On Sun, 7 May 2000, Bill Fenner wrote: > > >By "gratuituous arp" I was really saying "gratuitous arp reply". > >The machine needs to send a packet of the type > > > > arp reply 1.2.3.5 is-at 0:40:5:42:d6:de > > The ARP processing specified in RFC 826 says that if you have an entry for > the source IP address you update the hardware address no matter what the > opcode is (i.e. you can update your tables due to a request). Every IP > stack I've seen implements gratuitous ARP by sending a broadcast request > for itself. In normal ARP operation, replies are unicast so conceivably > an implementation that doesn't expect a broadcast reply might drop it. > Requests are normally broadcasted, and the ARP processing rules cause > broadcasted requests to update existing tables, so a broadcasted request > is a better choice for a gratuitous arp. > > tcpdump hides too much information in an attempt to make things look > pretty; it doesn't show the fact that the MAC information is included > in a gratuitous ARP. > > Bill > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message