Date: Sun, 7 May 2000 19:30:14 -0700 From: Bill Fenner <fenner@research.att.com> To: dhesi@rahul.net Cc: freebsd-current@freebsd.org Subject: Re: gratuituous arp for multiple IP addresses Message-ID: <200005080230.TAA09785@windsor.research.att.com>
next in thread | raw e-mail | index | archive | help
>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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200005080230.TAA09785>