From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Janos Farkas" Subject: Re: Broadcast ARP packets on link local addresses (Version2). Date: Thu, 6 Apr 2006 18:53:07 +0200 Message-ID: <493eee610604060953jcfdd2b6wdf773f4fb828aafa@mail.gmail.com> References: <17460.13568.175877.44476@dl2.hq2.avtrex.com> <44353F36.9070404@avtrex.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, pgf@foxharp.boston.ma.us, freek@macfreek.nl Return-path: To: "David Daney" In-Reply-To: <44353F36.9070404@avtrex.com> Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 4/6/06, David Daney wrote: > Janos Farkas wrote: > > Shouldn't it > > be more correct to not depend on the ip address of the used network, > > but to use the "scope" parameter of the given address? > RFC 3927 specifies the Ethernet arp broadcast behavior for only > 169.254.0.0/16. Presumably you could set the scope parameter to local > for addresses outside of that range or even for protocols other than > Ethernet. Since broadcasting ARP packets usually adversely effects > usable network bandwidth, we should probably only do it where it is > absolutely required. The overhead of testing the value required by the > RFC is quite low (3 machine instructions on i686 is the size of the > entire patch), so using some proxy like the scope parameter would not > even be a performance win. Indeed, I just have a bad feeling about hardwiring IP addresses this deep. The problems with "my" idea would be, summarily, after a day: Q: Is there are reason to use broadcast ARP semantics for other IP address ranges? A: Maybe, but no RFC defines that. Q: Is there are reason to NOT use broadcast ARP semantics for the defined IP address ranges? A: Maybe, but the RFC is against it. Q: Is there a reason to expect people (and tools) to use/define scopes? A: Probably, but it's still uncommon practice :) I mean, how many of us have 192.168.x.x addresses with "global" scope? I know I do. I'm still in a losing position :) Janos