Saturday, October 10, 2009

Multicast Roaming

L2: sessions are maintainted simply because the foreign ap (if configured properly) already belongs to a multicast group and traffic is not tunneled to a different anchor point on the network.
L3: depends on what tunneling mode is configured on the WLCs.  The IGMP messages sent from a wireless client can be affected.

Default mobility tunneling mode is asymmetrical.

Use the 239/8 block
Do not use 239.0.0.X or 239.128.0.X - overlaps with link local MACs and floods out all the switch ports even with IGMP snooping turned on.

WLCs drop any multicast packets to 12222, 12223, or 12224.
Multicast traffic is transmitted at the 6Mbs data rate on the 802.11A network.
If several WLANs try to transmit at 1.5MBps, packet loss occurs.

If the source of the multicast group is on a wired LAN, the source IP address for the multicast group is the management interface of the WLC.

If the source of the multicast group is a wireless client, the multicast packet is unicast, the WLC makes two copies of the multicast packet.  One copy is sent out the VLAN associated to the WLAN SSID on which it arrived.
--This enables receivers on the wired LAN to receive the multicast stream and the router to learn about the new multicast group.  The second copy of the packet is LWAPP encapsulated and sent to the LWAPP multicast group so that wireless clients can receive the multicast stream.

L2 switches: no configuration is required for multicast.  All IOS-based L2 switches have CGMP enabled by default.

ip igmp join-group []

Locating a faulty hop
To display info on the last hop router:
    show ip igmp
  show ip mroute
  show ip mcache
  show ip interface counts
  show ip mroute count

Using the RFF interface info, move to the last hop router to the first hop router following the IP address path.  Repeat all commands except show ip igmp.

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