From owner-freebsd-current Sun May 7 19:31:36 2000 Delivered-To: freebsd-current@freebsd.org Received: from mail-green.research.att.com (H-135-207-30-103.research.att.com [135.207.30.103]) by hub.freebsd.org (Postfix) with ESMTP id 7423D37B71D for ; Sun, 7 May 2000 19:31:34 -0700 (PDT) (envelope-from fenner@research.att.com) Received: from alliance.research.att.com (alliance.research.att.com [135.207.26.26]) by mail-green.research.att.com (Postfix) with ESMTP id 426FD1E003; Sun, 7 May 2000 22:31:33 -0400 (EDT) Received: from windsor.research.att.com (windsor.research.att.com [135.207.26.46]) by alliance.research.att.com (8.8.7/8.8.7) with ESMTP id WAA13970; Sun, 7 May 2000 22:31:32 -0400 (EDT) From: Bill Fenner Received: (from fenner@localhost) by windsor.research.att.com (8.8.8+Sun/8.8.5) id TAA09785; Sun, 7 May 2000 19:30:14 -0700 (PDT) Message-Id: <200005080230.TAA09785@windsor.research.att.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII To: dhesi@rahul.net Subject: Re: gratuituous arp for multiple IP addresses Cc: freebsd-current@freebsd.org Date: Sun, 7 May 2000 19:30:14 -0700 Versions: dmail (solaris) 2.2g/makemail 2.9a Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG >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