nanog mailing list archives

Re: The stupidity of trying to "fix" DHCPv6


From: "Ricky Beam" <jfbeam () gmail com>
Date: Mon, 13 Jun 2011 15:50:09 -0400

On Sun, 12 Jun 2011 09:45:01 -0400, Leo Bicknell <bicknell () ufp org> wrote:
In a message written on Sun, Jun 12, 2011 at 01:04:41PM +0200, Iljitsch van Beijnum wrote:
Like I said before, that would pollute the network with many multicasts which can seriously degrade wifi performance.

Huh?  This is no worse than IPv4 where a host comes up and sends a
subnet-broadcast to get DHCP.

Broadcast != Multicast. esp. when talking about wireless chipsets. I've yet to find a wifi chipset that didn't completely fuck-up when presented with even a low pps of multicast traffic. Broadcast traffic doesn't seem to bother them -- it doesn't attempt to filter them in any way, or really pay them any attention. If I had to guess, the chip firmware is individually transmitting multicast packets to each peer; a broadcast packet is sent once to all peers.

I've not had any wireless networks disrupted by broadcast traffic -- and with Radware load balancers in the network, there are *plenty* of broadcasts (ARP). Just a few 100pps of multicast and the AP fails. (linksys, netgear, even cisco... all broadcom crap radios.)

--Ricky


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