Date: Sun, 7 May 2000 19:40:27 -0700 (PDT) From: Rahul Dhesi <dhesi@rahul.net> To: Bill Fenner <fenner@research.att.com> Cc: freebsd-current@freebsd.org Subject: Re: gratuituous arp for multiple IP addresses Message-ID: <Pine.BSF.4.21.0005071940130.88776-100000@yellow.rahul.net> In-Reply-To: <200005080230.TAA09785@windsor.research.att.com>
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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
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