Date: Wed, 19 Sep 2001 11:05:53 -0700 From: Bakul Shah <bakul@bitblocks.com> To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> Cc: "Matthew Luckie" <kluckie@ihug.co.nz>, net@FreeBSD.ORG Subject: Re: arp X moved from Y to Z messages Message-ID: <200109191805.OAA10027@renown.cnchost.com> In-Reply-To: Your message of "Tue, 18 Sep 2001 10:56:55 EDT." <200109181456.f8IEutZ50461@khavrinen.lcs.mit.edu>
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> > The gateway's IP address actually refers to two different machines. > > Naturally the gateway is used quite a bit, and the syslog fills up with "arp > > X moved from Y to Z on fxp0" messages. > > That's really not the right way to do it, and probably doesn't balance > the load as well as you might think it would. The right way to do it > is to advertise a single *multicast* MAC address, allocated out of the > local MAC space (i.e., first two bits 11), and have both routers join > the group; then both will get all the packets and can decide which > ones to forward. This gives you automatic fail-over trivially. That is not valid according to the router requirements rfc (rfc1812), section 5.3.4: A router MUST NOT forward any packet which the router received as a Link Layer multicast unless the packet's destination address is an IP multicast address. A router SHOULD silently discard a packet that is received via a Link Layer broadcast but does not specify an IP multicast or IP broadcast destination address. When a router sends a packet as a Link Layer broadcast, the IP destination address MUST be a legal IP broadcast or IP multicast address. What Luckie does is clever but removing syslog messages seems like asking for trouble -- if two machines get the same IP address due to a mistake, tracking that down will be a bit more difficult. Redundancy should be handled by running the router discovery algorithm (e.g. routed) on each host and RIP or OSPF on the routers. Generally people use load balancing *between* routers and use a hefty enough router to handle all your local traffic on one net. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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