From owner-freebsd-net@FreeBSD.ORG Mon Jun 14 12:41:20 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 572EE106566C for ; Mon, 14 Jun 2010 12:41:20 +0000 (UTC) (envelope-from freebsd-net@m.gmane.org) Received: from lo.gmane.org (lo.gmane.org [80.91.229.12]) by mx1.freebsd.org (Postfix) with ESMTP id 0E10F8FC16 for ; Mon, 14 Jun 2010 12:41:19 +0000 (UTC) Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1OO8yc-0005t4-O2 for freebsd-net@freebsd.org; Mon, 14 Jun 2010 14:41:18 +0200 Received: from lara.cc.fer.hr ([161.53.72.113]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 14 Jun 2010 14:41:18 +0200 Received: from ivoras by lara.cc.fer.hr with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 14 Jun 2010 14:41:18 +0200 X-Injected-Via-Gmane: http://gmane.org/ To: freebsd-net@freebsd.org connect(): No such file or directory From: Ivan Voras Date: Mon, 14 Jun 2010 14:41:12 +0200 Lines: 27 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Complaints-To: usenet@dough.gmane.org X-Gmane-NNTP-Posting-Host: lara.cc.fer.hr User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US; rv:1.9.1.9) Gecko/20100518 Thunderbird/3.0.4 In-Reply-To: X-Enigmail-Version: 1.0.1 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 12:41:20 -0000 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.