Configuration Guidelines And Limitations - Cisco WS-C2950-24 Configuration Manual

Chapter 6 Configuring the System

Configuration Guidelines and Limitations

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MVR eliminates the need to duplicate television-channel multicast traffic for
subscribers in each VLAN. Multicast traffic for all channels is sent only once
around the VLAN trunk—only on the multicast VLAN. Although the IGMP leave
and join messages originate with a subscriber, they appear to be initiated by a port
in the multicast VLAN rather than in the VLAN to which the subscriber port is
assigned. These messages dynamically register for streams of multicast traffic in
the multicast VLAN on the switch. The access layer switch (S1 switch) modifies
the forwarding behavior to allow the traffic to be forwarded from the multicast
VLAN to the subscriber port in a different VLAN, selectively allowing traffic to
cross between two VLANs.
IGMP reports are sent to the same MAC addresses as the multicast data. The S1
CPU must capture all IGMP join and leave messages from subscriber ports.
Because the Catalyst 2900 and Catalyst 3500 hardware cannot distinguish IP
multicast data packets from IP multicast packets carrying IGMP protocol data, all
packets from subscriber ports destined for the configured multicast MAC
addresses are forwarded to the switch CPU, which distinguishes IGMP packets
from regular multicast traffic.
Follow these guidelines when configuring MVR:
• All receiver ports on a switch must belong to the same VLAN and must not
be trunk ports.
• In applications where the receiver ports represent subscribers to a service, we
recommend configuring receiver ports as follows:
Enable protected port on all receiver ports to isolate the ports from one
–
another.
Enable port blocking on all receiver ports to prevent unknown unicast
–
and multicast packets.
Before configuring MVR groups, configure all MVR parameters, including
•
the multicast VLAN. If you want to change the MVR parameters after MVR
groups have been configured, follow these steps:
a. Enter the no mvr command to disable MVR.
Enter the mvr vlan <vlan-id> command to change the multicast VLAN.
b.
Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
Configuring MVR
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