Once its NIC accepts the frame, the packet will be forwarded according the multicast routing rules based on the destination IP address. A router does not care about the discrepancy between the destination IP and MAC.So the hypotheses to verify or refute were: How does the IGMP Snooping really work? Does it add and remove multicast MAC entries to the CAM table, or does it perform its filtering based on actual IP headers and destination addresses? Obviously, it could be done either way, so the only answer was to do a lab experiment. However, this is much easier said than done. The purpose of IGMP Snooping is to allow the switch to learn about attached multicast receivers and the multicast groups they have subscribed into, so that in the ideal case, multicast flows are forwarded out only to the intended receivers and not flooded anymore. The only case I was not at all certain was with a switch running IGMP Snooping. Regardless of the method, once the frame is received and accepted by the NIC, the router should process the packet in the frame. This approach is used, for example, with Cisco 3620 routers that use the AMD Am79C971 controller. The interface controller may support multiple MAC addresses and masks or MAC address hash tables to cover entire ranges of MAC address space.The software-based MAC address filter may still be necessary to filter out unwanted multicast MAC addresses. If the interface controller supports a special mode for receiving all multicasts, it can be used in place of promiscuous mode, as it will prevent issues with unintended receiving and processing of unicast frames. Because this behavior could potentially lead to ill behavior such as looping of unicast packets for no apparent reason (this was a bug in Dynamips v0.2.11 and older - read this discussion where I submited a correction to Dynamips and explained the rationale), IOS will maintain an additional software-based MAC address filter to filter out frames that were received by the NIC but are not really intended to be processed by this router. As an example, this approach is used with Cisco routers using Gt96k FastEthernet controller (2691, 1841 to name a few).
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