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Multicast and the Wireless LAN Controller (WLC)

 

 

Introduction

 

 

Multicast and the Wireless LAN Controller (WLC)

 

Solution

 

Lots of people seem to be confused by multicast, in general, and specifically how the WLC comes into the mix.  This document is meant to be an overview of what needs to be done for the WLC to participate in multicast.  It is by no means an indept configuration for a networks multicast configuration.

 

So to that end, here we go.

 

First, let's start with the two modes the controllers operate with:

 

Multicast - Unicast

 

This is the easiest method to use.  When the WLC receives a Multicast packet, it replays that packet to every AP that is connected.  Now this does work, but can be very network intense, as every AP gets the stream.  So if you have 100 AP, there are 100 streams, 300 AP 300 streams.

 

Multicast - Multicast

 

This is the better method to use.  With this method, the AP will join to a multicast group, that you configure, preferably in the 239.x.x.x administratively scoped space.  Now when the WLC gets a multicast packet, it replays it once to the group.

 

WLC side

 

Select Multicast - Multicast and configure your group, each WLC in your mobility group should use a unique address.  For the WLC you are done.

 

Network side

 

you need to enable multicast routing, if it's not enabled already, and you need to pim enable, the following VLANs.  Management, AP-Manger, all the VLAN that the AP are in, as well as the VLAN(s) where the clients that will receive the stream will be.

 

In my lab, VLAN 20 is the management, VLAN 10 is for AP, and VLAN 30 is where my clients are.  So under all of these SVI I need to issue the multicast commands.

 

You should be able to issue show ip mroute, show ip igmp groups, and all the other multicast commands to validate that the group for the AP is built properly.

 

On the WLC, there is also the ability to enable IGMP snooping.  With this enabled, the WLC will hold it's own snooping table for the IGMP messages that it receives, so that it knows who needs to get the stream.

Comments
Cisco Employee

WOW!! This is amazing.. This has everything.. Short and Sweet!!

New Member

It's indeed really helpful.

A short question, does this apply for the Wism as well??

Thank you

This applies to all controllers, that have been released to date.

New Member

Stephen - Are you sure about all the controllers - I happen to see that the 2016 has a limitation on the multicat forwarding .

After the network starts sending multicast packets the controller forwards the multicast packets for a few minutes and after that it refuses to forward . I happen to see some mbuff getting full in logs .

There was a bug for the same which said multicast not supported on 2106 platforms .

New Member

It's amazing to me how complex multicast can be, yet you've been able to lift the veil (on this subject at least) very efficiently.  Kudos to you Stephen, you've done an excellent job here!  Looks like I've got some changes to do in my network

Indeed this is amazing information. Thanks Stephen.

New Member

If i may add, software version 7 is much more efficient in deliverying multicast!Combine the instructions with the latest software version to receive better results!

New Member

I have a question if you dont mind.

For Multicast-Multicast (recommended) you say

Select Multicast - Multicast

Where is this selection available to be made?

I have a 5508 & am running 7.0.235.3 & do not see anywhere in the wlc the Multicast - Multicast, let alone where to configure the group.

What I want is to enable the VoIP ssid/interface to use multicast for Music on Hold. I dont necessarily need this on any other vlan.

We have a series of remote locations all running HREAP with 3502AP's & each facility has the same VoIP vlan/ssid which requires multicast for MOH.

Thank you

New Member

Wow.. a 4 year old article and still just as relevant today.

We had recently moved all our SVIs from a set of 6509s to Nexus 7Ks and in the course of troubleshooting Vocera issues I realized we had added the "ip pim sparse-mode" command to our Voice SVI but had forgot to enable it on our AP management SVIs. Once that was done "sh ip igmp groups" verified it was working.

Thank you for the succinct information Stephen.

 

-spaz-

New Member

Wireless

New Member

nice and simple , just make sure you dont have a ACL on your AP's. 

if you do then it seems you l need to enable 224.0.0.0/24 (igmp) and the range you use for the AP multicast address/s 

Question: What happens if you have multiple WLC's on the same Multicast address ?