Date: Mon, 7 Nov 2005 14:40:43 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Gleb Smirnoff <glebius@FreeBSD.org> Cc: arch@FreeBSD.org Subject: Re: ARP request retransmitting Message-ID: <20051107143620.P9690@fledge.watson.org> In-Reply-To: <20051107140451.GU91530@cell.sick.ru> References: <20051107140451.GU91530@cell.sick.ru>
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On Mon, 7 Nov 2005, Gleb Smirnoff wrote: > I have a proposition on changing the behavior of ARP retransmitting. > Currently we after sending several ARP requests, sending ARP requests > for given IP is suppressed for some interval (by default 20 seconds). > Probably this feature was designed in early 90th, when sending one > additional broadcast packet was an expensive thing. > > I suggest to keep sending ARP requests while there is a demand for this > (we are trying to transmit packets to this particular IP), ratelimiting > these requests to one per second. This will help in a quite common case, > when some host on net is rebooting, and we are waiting for him to come > up, and notice this only after 1 - 20 seconds since the time it is > reachable. While networks have gotten a lot faster in the last few years, I've noticed that many of the ones I deal with have also gotten a lot larger in terms of number of hosts. This has been possible both because of the absolute increase in bandwidth, and also because of the widespread use of switches to suppress unnecessary unicast traffic to segments. I worry that significantly increasing the amount of broadcast traffic will be a problem for sites with large bridged network configurations. On the other hand, they already have to deal with things like windows network neighborhoods, various service discovery protocols, and so on. Do you have any information on what other operating systems may have done in terms of tweaking ARP for improved responsiveness? I imagine we can't be the first to discuss such changes, and if there is already a widely deployed system with ARP adaptations of this sort, it would be interesting to know if they've seen any problems or have recommendations. Robert N M Watson
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