Maithri B. is a customer support engineer at the Cisco Technical Assistance Center in Bangalore, India. She has four years of experience and has worked on a wide range of Cisco wireless products and technology such as autonomous IOS (aIOS) access points, wireless LAN controllers, wireless VoIP phones, wireless control systems, network control systems, and mobility services engines. She has also worked in LAN switching technology.
Multicast on Cisco Wireless LAN Controllers
A: The configs covered in this webcast are applicable to all versions and platforms of Cisco WLC. There are some new features added in the newer releases for optimization of multicast but those have not been explained in this webcast
A: Yes you can use the Apple TV and Airplay functionalist on two different WLANs (subnets) via the Cisco Bonjour Gateway Deployement which enables the discovery of Apple devices in multi-subnet environment.
A: Yes, we would still need multicast routing enabled end to end even on wired network
A: Yes, it is recommended that each controller in the network is configured with a different multicast group IP. The reason is because we want to avoid the multicast traffic on one controller flooding to all other controllers and APs in the network. The multicast group IP configured should be local only to one WLC and the APs registered to it
A: We would use Multicast-Unicast mode in both the cases stated above i.e the wired network is not multicast ready or we need multicast support across EoIP tunnel. However enabling multicast-unicast mode will overload the WLC (depending on the number of clients and APs) as it has to replicate each packet into a unicast and send it to each AP. This consumes lot of processing power on the controller. This is one of the reasons why the Cisco 2500 series WLC does not have the Multicast-Unicast option anymore
A: When we configure a multicast group IP on the controller, an LWAPP AP multicast group is created. All the APs that register to the controller are automatically a part of this group. However each LWAPP AP multicast group should have only one controller. Each controller should have its own Multicast group IP
A: Yes the multicast traffic from the controller will always get sent to all the APs. If you are having APs are different branch sites (H-REAP/Flexconnect mode) they would also receive all the Mcast traffic. The APs will then discard the packets if there are no clients requesting for the mcast traffic. This behavior cannot be modified
Q: Does all of it apply to H-Reap also?
A: All the configs should be applied for H-REAP APs also. However Multicast-Multicast mode is supported only on Local mode and H-REAP Centrally switched WLANs. H-REAP Local switching can only do Multicast-Unicast mode.
A: It is recommended to keep the broadcast forwarding enabled to ensure all the necessary network protocols that function via broadcast would work well. This also ensures that L2 multicast is allowed.
A: Multicast should be enabled to support Video streaming. However it is not necessary that video streaming should be enabled to support multicast. Enabling video streaming will ensure reliable delivery of multicast however is not a mandatory option.
A: Yes it is available
Q: For that last answer, any clues as to when the 7.4 code will be release to resolve the bonjour gateway issue. I currently have two solutions in place in order to multicast across vlans, just wanted to know when the code will be released?
A: 184.108.40.206 is available on CCO for download
A: Yes, that is correct. Smaller switches can function with only "ip multicast-routing" enabled.
A: 7.4 and above.
A: The WLC will bridge all the multicast traffic from the wired to wireless side and vice versa. I am not very clear about what is meant by "clients on different VRF" but if you are referring to clients on different subnet that the AP/WLC management, we have to make sure to have L3 multicast enabled.
A: It is similar to pim-dense mode. In Multicast-Unicast mode, each multicast packet is converted into a unicast packet and flooded to all the APs registered on that controller. Hence it is more CPU intensive and adds overhead on the controller.
A: It is not recommended to set the WLC as a RP candidate. WLC multicast group IP is a local IP on the WLC configured for multicast traffic exchange between the controller and its AP. WLC cannot be made as RP for other multicast IPs
A: 7.4 software is released on CCO for all supported controller platforms. It was just getting uploaded on CCO when you checked
A: There is no Cisco tool but there are many third party tools available online that can be used for simulating multicast traffic. One such tool is attached to this FAQ.
A: There is no Cisco tool but there are many third party tools for mcast traffic generators and traffic receivers. Any of these can be used for troubleshooting.The best way to analyze mcast traffic would be to take a packet capture on client and span capture from switchport going to WLC.
A: Lot of applications and wireless devices need multicast. Video streaming, file sharing applications etc need multicast enabled on WLC. There are also certain type of client devices like Vocera bades/Spectralink phones that need multicast for optimum performance.
A: If the BYOD devices are going to use multicast then it is mandatory to have multicast enabled on the WLC to make sure the WLC sends the multicast packets to all its APs and clients. If multicast is not enabled, BYOD devices will still connect to WiFi network but lot of applications that use multicast over wireless will not function.
A: VLC media player is one of the tools that we often use to send mcast stream. This can be used for testing, should not be an issue.
A: As Flexconnect APs in local switch mode do not support multicast-multicast mode, we need to use Multicast-Unicast mode and enable Multicast routing on that VLAN.
A: You have a dedicated WLAN configured for your iPad users. These users might be using most of the Bonjour based applications on Apple like Airplay, Airprint etc. Enabling multicast on wireless will ensure that these devices are able to discover each other via wireless without any issues.
A: MCAST , VNC player.I have also attached a sample multicast tool to this FAQ doc.
A: Wireless Multicast is always sent at the highest mandatory data rate enabled for that network.
A: There is no specified bandwidth requirement for enabling mcast on WLC
A: On older controller platforms like 4400 series and WiSM, multicast was handled at the CPU level. On the newer platforms like 5508, WiSM2 etc we have fastpath enabled on the controller that allows data switching at the forwarding plane.
A: WLC analyzes IGMP reports from clients and creates an MGID table to keep track of which clients are requesting for multicast traffic. Once a client stops requesting for mcast traffic, the client entry will be present on the WLC till the IGMP timeout value expires and then the client entry gets deleted. The default value is 60 secs.
A: Yes that's right as we don't have the Multicast-Multicast mode support for Flexconnect Local Switching mode. However if the WLAN is doing Central switching then you can use multicast-multicast mode
A: Yes, the MCAST generator tool would source continuous stream of traffic to the configured multicast destination IP and the MCAST receiver tool would join this multicast group to receive the traffic
A: No, the end users will NOT use the multicast group IP on the WLC. The local LWAPP Multicast group IP is for communication and sending mcast traffic from WLC to APs and vice versa. The end clients are not aware of this IP.
A: We would still need mcast enabled on wired side as Bonjour Gateway is only going to cache the request and can forward if request is from a different vlan. Without bonjour gateway, it is required that the mcast source and destination are on the same vlan and it would still need multicast-routing enabled on the wired side.
A: No, 7.4 does not have this support. The developement team is working on this feature however we do not have an ETA on when this will be available.
A: By default Multicast is enabled on the IOS AP and hence multicast traffic can pass across without issues. However at times having "igmp snooping" enabled might cause issues in which case we can disable it and multicast should work fine.
A: At present we do not have the option to enable multicast on a per-WLAN basis. Generally enabling mcast globally should not cause any issues. However in very large enterprise networks (~5k - 10k clients) if each of the SSID will have users that are going to request multicast traffic, then there will be too many mcast packets in the network and this might increase the CPU utilization on the WLC.
A: This might take a while as the BU is working on it. We do not have an ETA as of now.
A: There is no way at present to monitor bandwidth consumption on WLC due to multicast.
A: Multicast traffic can be bandwidth intensive. Giving a higher priority to multicast traffic can cause the WLC to drop other important traffic network/user data. Hence it is recomended to leave Mcast on BE QoS level unless a specific mcast application requires prioritization.
A: We can use any of the available packet capture analyzing tools to monitor mcast traffic flow. One commomly used example is Wireshark.
A: We do not have the option to enable multicast only on specific APs but we have the VLAN Select feature on the WLC by which we can choose to enable multicast only on certian client subnets. This way we can limit the traffic on interfaces that do not need Multicast
A: Bonjour is a protocol specifically used by Apple devices for file sharing purposes. Enabling multicast on WLC will make sure Bonjour traffic is sent across from the source to the destination. This can be done on 220.127.116.11
A: I have not seen this issue with Airplay so far but if you are seeing this in your netowrk, i would suggest to open a TAC case to troubleshoot further
The mcast tools attached to this doc are 3rd party tools, not Cisco tools