Date: Mon, 14 Jun 2010 14:41:12 +0200 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-net@freebsd.org Subject: Re: VLANs, routing, multicast and HP switches, oh my... Message-ID: <hv5816$7t4$1@dough.gmane.org> In-Reply-To: <AANLkTin8Tmcz19rPgjma6Pj_O0vpG7LfZkWkDskLT3zj@mail.gmail.com> References: <AANLkTikZhyrufjNuUPhNDlDZ4iKp-KWN-AgcwUt1g1_p@mail.gmail.com> <huqr8u$uak$1@dough.gmane.org> <AANLkTin8Tmcz19rPgjma6Pj_O0vpG7LfZkWkDskLT3zj@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
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.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?hv5816$7t4$1>