So, the destination MAC address of multicast traffic cannot be the burned-in MAC address of the network interface of an individual computer. But the multicast traffic is sent to a group of computers. Usually the destination MAC address for unicast type of network traffic is the burned-in MAC address of the receiving computer’s network interface. When an IPv4 datagram are sent as unicast, the Ethernet frame which is encapsulating the IPv4 datagram contains sender and receiver MAC addresses as the source and destination MAC addresses respectively. Address information at IPv4 datagram is source and destination IPv4 addresses, but the address information at layer 2 frame is source and destination MAC addresses. When a unicast data packet is sent to the network, the layer 3 (network layer) IPv4 datagram is encapsulated within layer 2 (datalink layer) frame. Why we need multicast IPv4 address to multicast MAC address mapping Advantages and disadvantages of multicast.What is directed broadcast in IPv4 and how directed broadcast works.What is limited broadcast in IPv4 and how limited broadcast works.IPv4 addresses, IPv4 Address Classes, IPv4 Address Classifications.IPv4 Protocol, IPv4 header and fields of IPv4 header.What is MAC address or Layer 2 address or physical address.TCP/IP Data Encapsulation and Decapsulation.Binary Decimal and Hexadecimal numbers and conversions.I strongly suggest you to visit and learn below lessons before reading further about multicast IPv4 address (Class D address) to IPv4 multicast MAC address mapping. We have learned that Class D multicast IPv4 addresses ranging from 224.0.0.0 to 239.255.255.255 are reserved as IPv4 multicast addresses. In this lesson, we will learn about multicast IPv4 address (Class D address) to IPv4 multicast MAC address mapping. We have learned about Class D multicast IPv4 addresses in last lesson. Since the static CAM is recommended but not mandatory, it seems only wise to go with the simplest solution.Multicast IPv4 address to MAC address mapping Last question: in order to disable snooping on the 65xx, shouldn't it be enabled in the first place, or is it a default behaviour? I though that igmp snooping was possible, if you already had multicast routing enabled. In order to avoid this, static CAM entries should be added on the access switch - pointing to the physical servers - but also on all other switches - pointing out their uplinks - aswell as on the 65xx (core switch) pointing towards the access switch and on the EtherChannel ports (connecting are two 65xx)? If vtp pruning were enabled, then these static CAM should be configured on all switches with ports on the same vlan as the NLB. In our environment VTP pruning is not enabled (yet!!!), so flooding will affect all switches in the domain. Static ARPs should be applied on the 65xx which performs intervaln routing. For a network with a small number of routers touching the NLB subnet I recommend staticly configured entries. Newer Windows versions can be enabled for IGMP, but this may not work for all switches as some models (notably Catalyst 3750 and similar) forward multicast at L2 based on destination IP (which we can't determine from the NLB IGMP reports) rather than MAC. This is because by default NLB servers do not generate IGMP reports which are the primary mechanism switches use to constrain multicast traffic.
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