Cisco 224.0.0.x flood

In general, We know 2 routers in the same segment with OSPF or EIGRP, they will bcome neighbor. But how about the Layer 2 device, How does it know which port is join the EIGRP multicast group 224.0.0.10??

There is a doc in cisco.com about how switch process the reserved, destination, multicast IP addresses. It's Source-Only Networks.

Source-Only Networks

In a source-only network, switch ports are connected to multicast source ports and multicast router ports. The switch ports are not connected to hosts that send IGMP join or leave messages.

The switch learns about IP multicast groups that alias with reserved, destination, multicast IP addresses (224.0.0.x) from the IP multicast data stream by using the source-only learning method. The switch forwards traffic that aliases with these multicast addresses only to the multicast router ports.

The default learning method for traffic that aliases with reserved, destination, multicast IP addresses is IP multicast-source-only learning.Traffic that does not alias with these multicast addresses is forwarded to both the multicast source ports and multicast router ports. You cannot disable IP multicast-source-only learning for the traffic with reserved, destination, multicast IP addresses.

By default, the switch ages out forwarding-table entries that were learned by the source-only learning method and that are not in use. If the aging time is too long or is disabled, the forwarding table is filled with unused entries that the switch learned by using source-only learning or by using the IGMP join messages. When the switch receives traffic for new IP multicast groups, it floods the packet to all ports in the same VLAN. This unnecessary flooding can impact switch performance.

If aging is disabled and you want to delete multicast addresses that the switch learned by using source-only learning, re-enable aging of the forwarding-table entries. The switch can now age out the multicast addresses that were learned by the source-only learning method and are not in use.