Hi Tariq, I think it's going to vary from vendor to vendor and what it means to have "multicast enabled" - and how each vendor handles multicast traffic - and the type of multicast traffic (Whether it's SSDP [239.255.255.250] - MDNS [224.0.0.251] Link-Local or something completely different). Multicast is one of my recent rabbit holes that I'm still trying to fully grasp and understand in a wireless environment. We're an Aruba Environment and utilize "Drop Broadcast and Unknown Multicast" traffic on our wireless networks. That prevents broadcast/multicast traffic from being flooded out to our wireless clients - however, if one of associated clients has subscribed to a multicast group - then the traffic will be allowed and has worked fairly well over the past couple years. We're now making use of Aruba AirGroup for managing SSDP/mDNS traffic for Chromecasts, Apple TVs, Rokus, etc.
Having multicast enabled without any inhibitors/restrictions can have significant performance issues due to heavily chatty protocols (SSDP/mDNS) constantly running in the background of devices. A real-world example with a previous vendor: some of our lectures halls saw consistent Channel Utilization 50-60% with several complaints of people being unable to associate to the WLAN (if they did - it was to an AP three floors up). Upon noticing "multicast" was enabled for this particular WLAN - settings had a habit of unfortunately reverting (despite write mem/save configs) - I waited till late at night - disabled it and saw a massive improvement. - Channel Utilization was no longer consistently at 50-60%. - Issue was resolved for the 2 large lecture halls that had this issue. - The big evidence - we saw an average increase in 2,000 clients campus wide for the controllers on a weekly basis from that night forward - devices that weren't able to associate before were now available to. - Traffic significantly dropped by 50% (multicast traffic being dropped). The behavior of clients increasing/but throughput decreasing (reduction in chatty multicast traffic being dropped) was a behavior seen across multiple vendors by the way - which was perplexing at first but made more sense over time. With a small exception of "Informicast" - I've seen multicast over wireless areas in our environment has more of a "convenience" feature - unless you're a Chromecast where some form of multicast is required to control/use the device. Christopher Johnson Wireless Network Engineer AT Infrastructure Operations & Networking (ION) Illinois State University (309) 438-8444 Stay connected with ISU IT news and tips with @ISU IT Help on Facebook<https://www.facebook.com/ISUITHelp/> and Twitter<https://twitter.com/ISUITHelp> From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU] On Behalf Of Lee H Badman Sent: Wednesday, August 16, 2017 5:40 AM To: WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU Subject: Re: [WIRELESS-LAN] multicast enabled on your wireless network? Have seen many single-room vendor devices that "require" multicast- until you press the vendor and they magically reveal an alternative way. Haven't found a legitimate need on WLAN yet, and any testing has not really been at scale for me. Lee -----Original Message----- From: Tariq Adnan [tariq.ad...@sydney.edu.au] Received: Tuesday, 15 Aug 2017, 20:11 To: WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU [WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU] Subject: [WIRELESS-LAN] multicast enabled on your wireless network? Hello everyone, Just checking if you guys have multicast enabled on your wireless network and if you have come across any performance issues arising after enabling it? Is multicast widely used in your network? I am working on a POC which has requirements that can be fulfilled by either enabling multicast or converting few APs to flexconnect mode. I am more in favour of later method but again want to know your views. Thanks, - Cheers, Kind regards, Tariq Adnan ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss.
