[toc:faq]
Introduction
Multicast Sniffing
Solution
The controller performs multicasting in two modes:
- Unicast mode—In this mode, the controller unicasts every multicast packet to every AP associated to the controller. This mode is inefficient but might be required on networks that do not support multicasting.
- Multicast mode—In this mode, the controller sends multicast packets to an LWAPP multicast group. This method reduces overhead on the controller processor and shifts the work of packet replication to your network, which is much more efficient than the unicast method.
- You can enable multicast mode using the controller GUI or CLI.
IGMP Snooping on WLC
In controller software release 4.2, IGMP snooping is introduced to better direct multicast packets. When this feature is enabled, the controller gathers IGMP reports from the clients, processes the reports, creates unique multicast group IDs (MGIDs) from the IGMP reports after checking the Layer 3 multicast address and the VLAN number, and sends the IGMP reports to the infrastructure switch. The controller sends these reports with the source address as the interface address on which it received the reports from the clients.
The controller then updates the access point MGID table on the AP with the client MAC address. When the controller receives multicast traffic for a particular multicast group, it forwards it to all the APs. However, only those APs that have active clients listening or subscribed to that multicast group send multicast traffic on that particular WLAN. IP packets are forwarded with an MGID that is unique for an ingress VLAN and the destination multicast group. Layer 2 multicast packets are forwarded with an MGID that is unique for the ingress interface.
Note: IGMP snooping is not supported on the 2000 series controllers, the 2100 series controllers, or the Cisco Wireless LAN Controller Network Module for Cisco Integrated Services Routers.
Guidelines for Using Multicast Mode
Use these guidelines when you enable multicast mode on your network:
The Cisco Unified Wireless Network solution uses some IP address ranges for specific purposes. Keep these ranges in mind when you configure a multicast group: Although not recommended, any multicast address can be assigned to the LWAPP multicast group; this includes the reserved link local multicast addresses used by OSPF, EIGRP, PIM, HSRP, and other multicast protocols.
Cisco recommends that multicast addresses be assigned from the administratively scoped block 239/8. IANA has reserved the range of 239.0.0.0-239.255.255.255 as administratively scoped addresses for use in private multicast domains. See the note for additional restrictions. These addresses are similar in nature to the reserved private IP unicast ranges, such as 10.0.0.0/8, defined in RFC 1918. Network administrators are free to use the multicast addresses in this range inside of their domain without fear of conflict with others elsewhere in the Internet. This administrative or private address space must be used within the enterprise and its leave or entry blocked from the autonomous domain (AS).
Note: Do not use the 239.0.0.X address range or the 239.128.0.X address range. Addresses in these ranges overlap with the link local MAC addresses and flood out all switch ports, even with IGMP snooping turned on.
Cisco recommends that enterprise network administrators further subdivide this address range into smaller geographical administrative scopes within the enterprise network to limit the "scope" of particular multicast applications. This prevents high-rate multicast traffic from leaving a campus (where bandwidth is plentiful) and congesting the WAN links. It also allows for efficient filtering of the high bandwidth multicast from reaching the controller and the wireless network.
When you enable multicast mode on the controller, you must configure an LWAPP multicast group address on the controller. APs subscribe to the LWAPP multicast group using Internet Group Management Protocol (IGMP).
- Cisco 1100, 1130, 1200, 1230, and 1240 APs use IGMP versions 1, 2, and 3. However, Cisco 1000 Series APs use only IGMP v1 to join the multicast group.
- Multicast mode works only in Layer 3 LWAPP mode.
- APs in monitor mode, sniffer mode, or rogue detector mode do not join the LWAPP multicast group address.
- When you use controllers that run version 4.1 or earlier, you can use the same multicast address on all the controllers. If you use controllers that run version 4.2 or later, the LWAPP multicast group configured on the controllers must be different for each controller used on the network.
- If you use controllers with version 4.1 or earlier, the multicast mode does not work across intersubnet mobility events, such as guest tunneling, site-specific VLANs, or interface override that uses RADIUS. The multicast mode does work in these subnet mobility events when you disable the Layer 2 IGMP snooping/CGMP features on the wired LAN.
In later versions, that is, 4.2 or later, the multicast mode does not operate across intersubnet mobility events, such as guest tunneling. It does, however, operate with interface overrides that use RADIUS (but only when IGMP snooping is enabled) and with site-specific VLANs (access point group VLANs).
- The controller drops any multicast packets sent to the UDP port numbers 12222, 12223, and 12224. Make sure the multicast applications on your network do not use those port numbers.
- Multicast traffic is transmitted at 6 Mbps in an 802.11a network. Therefore, if several WLANs attempt to transmit at 1.5 Mbps, packet loss occurs. This breaks the multicast session.
Configuring Multicast (Using Multicast-Multicast Mode)
Select Mutlicast - Multicast and configure your group, each WLC in your mobility group should use a unique address.
Enable multicast routing on the L3 device and enable PIM on the following VLANs. Management, AP-Manger, VLAN on which the AP are in and as well as the VLAN where the cleints that will receive the multicast stream. Example :
VLAN 40 is the WLC management, VLAN 40 is for AP, and VLAN 50 is where my clients are. So under all of these SVI I need to issue the multicst commands.
Issue all Multicast show command to verify, example : show ip mroute, show ip igmp groups to validate that the group for the AP is built properly.
We can also enable IGMP Snoping on the WLC. The WLC will hold it's own snooping table for the IGMP messages that it receives, so that it knows who is requesting the stream.
On Wireless LAN Controller
Enable Global Multicast on the WLC and Enable Multicast – Multicast mode on the WLC
Once the client sends the multicast join, we will see the below on the WLC MGID
Multicast configuration on Wired network
Configure Multicast routing Globally and then enable PIM on each interface..
6504-WLCBUG#sh run | i multicast
ip multicast-routing
6504-WLCBUG#sh run int vla 50
Building configuration...
Current configuration : 119 bytes
!
interface Vlan50
description // WLAN DHCP pool VLAN //
ip address 172.16.1.1 255.255.255.0
ip pim dense-mode
end
6504-WLCBUG#sh run int vla 40
Building configuration...
Current configuration : 121 bytes
!
interface Vlan40
description // Management Vlan //
ip address 10.105.135.136 255.255.255.128
ip pim dense-mode
end
6504-WLCBUG#sh ip pim interface vlan 40
Address Interface Ver/ Nbr Query DR
DR Mode Count Intvl Prior
10.105.135.136 Vlan40 v2/D 0 30 1 10.105.135.136
6504-WLCBUG#sh ip pim interface vlan 50
Address Interface Ver/ Nbr Query DR DR
Mode Count Intvl Prior
172.16.1.1 Vlan50 v2/D 0 30 1 172.16.1.1
6504-WLCBUG#sh ip mroute
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected,
L - Local, P - Pruned, R - RP-bit set, F - Register flag,
T - SPT-bit set, J - Join SPT, M - MSDP created entry,
X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement,
U - URD, I - Received Source Specific Host Report,
Z - Multicast Tunnel, z - MDT-data group sender,
Y - Joined MDT-data group, y - Sending to MDT-data group
V - RD & Vector, v - Vector
Outgoing interface flags: H - Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 239.255.255.255), 4d17h/00:02:03, RP 0.0.0.0, flags: DC
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Vlan40, Forward/Dense, 4d17h/00:00:00
(*, 239.254.0.3), 2w1d/00:02:07, RP 0.0.0.0, flags: DC
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Vlan40, Forward/Dense, 3d10h/00:00:00
(*, 224.0.1.40), 2w1d/00:02:13, RP 0.0.0.0, flags: DCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Vlan11, Forward/Dense, 2w1d/00:00:00
Packet Captures
Topology
Wired PC ----------- 6500 Switch -------- WISM ------- AP )))) ((((( Wireless Client
Vlan 50 Vlan 40 Vlan 40 Vlan 40 Vlan 50
MCAST Traffic Generator Tool is used on the Wired PC to Generate Multicast Stream – Continuous UDP packets.
Wired Wireshark packet capture on the MCAST generator
Windows Netmon Capture on the Mcast packet generator
MCAST Receiver Tool is used on the Wireless Client to Receive the Multicast traffic from the Source (Wired PC).
Wireshark Captures on the Wireless interface of the Wireless client
Netmon Capture on the Wireless interface of the Wireless Client
