From owner-freebsd-net@FreeBSD.ORG Mon Jun 14 20:25:08 2010 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id EBF12106564A for ; Mon, 14 Jun 2010 20:25:07 +0000 (UTC) (envelope-from kurt.buff@gmail.com) Received: from mail-yx0-f182.google.com (mail-yx0-f182.google.com [209.85.213.182]) by mx1.freebsd.org (Postfix) with ESMTP id 9F4A68FC18 for ; Mon, 14 Jun 2010 20:25:07 +0000 (UTC) Received: by yxm34 with SMTP id 34so2011952yxm.13 for ; Mon, 14 Jun 2010 13:25:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type; bh=09w0/W63eZ0JQ/30gITLVELz2XkG8163q/6oQMyMQ3M=; b=v4MB7Wi68XA2/pN9BxNF4hdg8E08zgAZlCjoQQ+LYecJcZQtsJFWzJ4xuEfL+kX5Ii NNQW27vXuN5k75oVUBvj40DZyMon0D07AqLZ1FMZoP/ROllolDJSLQpav4oRDoQotxt4 x+G/BSbMq1wY5piOsnN0gdz8uRnYDrNl3zpJ4= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=UPeGZBzKWJUsUsKTHFfHtSCTYCUjZhXfUWJEJzOBqorfxix6b7xQk8aQW9d/QlFxLp 4/wdkcTqNBIyVhALIbmULq5frHL9UlqpKW2TSLXdYysPG6E0Q7boKdBRNgxJ0bzO9gb6 vREdYdFJCCxl8y8O7K3uGL0/Oj+L6ewLjpg6g= MIME-Version: 1.0 Received: by 10.101.11.10 with SMTP id o10mr5149480ani.18.1276546626963; Mon, 14 Jun 2010 13:17:06 -0700 (PDT) Received: by 10.231.38.8 with HTTP; Mon, 14 Jun 2010 13:17:06 -0700 (PDT) In-Reply-To: References: Date: Mon, 14 Jun 2010 13:17:06 -0700 Message-ID: From: Kurt Buff To: freebsd-net@freebsd.org Content-Type: text/plain; charset=UTF-8 Subject: Re: VLANs, routing, multicast and HP switches, oh my... X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 14 Jun 2010 20:25:08 -0000 On Mon, Jun 14, 2010 at 05:41, Ivan Voras wrote: > On 06/12/10 23:22, Kurt Buff wrote: > >> Again - they'll be putting up to 200 busy machines on each subnet. It >> seems reasonable to limit the broadcast domains with VLANs. > > I know that everyone begins to talk about "limiting the broadcast > domains" when talking about VLANs sooner or later but I have never > managed to learn exactly why this would be the biggest benefit of using > VLANs. > > Except if you are explicitly researching broadcast communication, the > only times a modern Ethernet will see broadcast packets is: > > 1) ARP packets when the machines are brought up or contacted the first time > 2) router announcements, RIP & similar > 3) Windows NetBIOS / Windows Networking workgroup name resolving > (analogous to ARP). > > Is there really so much broadcast traffic of these categories in a > network of 200 machines? And except if you are going to divide VLANs so > that each has a dedicated set of switches and cabling, with each VLAN > consisting of a dozen machines or so, many of these broadcast packets > will travel through the same cables and the same switch so you won't > magically get better performance out of it. You won't get away from > routing announcements and routing IP between VLANs will also result in > ARP requests on the destination side. I knew I should be explaining this better. I can only plead lack of time - I'm being rushed for lots of things at work and home at the moment, so haven't spent as much care on the explanation as I should have. My apologies for that. We'll be simulating installations of our software and hardware for customer installations that have WANs between sites, with several complementary applications, including a multicast app that is critical to the whole effort. While it's a bit much to expect us to be able to simulate a WAN at this point, I want to be able to simulate at least two subnets with routed multicast between them. One of the subnets will have as many as 200 simulated hosts on it, the others perhaps not so much. The majority of these machines will be Windows-based, so I expect broadcast traffic to be higher - but I also take your point about the packets traveling over the same wire. It would be best if I could get a multiport router - perhaps a layer3 switch (I'd love to get them an HP 3400cl) - but that costs much money that I don't have to spend at the moment. I'll set up the VLANs on that port and see how it goes. Kurt