Hi Sarah,
The port on the switch reside the hardware ASICs aka PFE (packet forwarding engine) and a group of ports belong to one PFE. Each switch will have multiple ASICs/PFEs.
Ingress PFE performs destination MAC address lookup after checking source mac lookup (for MAC learning). If destination is unknown unicast, the ingress PFE replicates the packet multiple times so that there is 1 copy for each of the local ports that are in the same VLAN as the ingress port, and 1 copy for each of the VCP ports. The same lookup and replication processes take place on all the other PFEs if the EX4200 is part of a virtual chassis as these PFEs receive the packet one after the other on the VC backplane.
The same process as mentioned above applies for unregistered multicast i..e if destination is unregistered multicast, the ingress PFE replicates the
packet multiple times so that there is 1 copy for each of the local ports that are in the same VLAN as the ingress port, and 1 copy for each of the VCP ports.
For L2 registered multicast packets (i.e. through IGMP snooping) with either unknown or known source MAC address, the forwarding process and packet flow is almost
identical to those of L2 unregistered multicast packets, except:
* Instead of flooding to all ports, registered multicast packets are only replicated to those ports belonging to same registered IP multicast group and are in the same VLAN as the source port.
* One copy of the registered multicast packet will still be transmitted out of each of the VCP ports of each PFE so that it reaches all of the PFEs in the VC.
Note that in case of unknown source-MAC, the MAC learning is done by the CPU though.
In simple words, to answer your question the unknown unicast or multicast packets are flooded to all ports in the same VLAN at the hardware level.
Hope this helps.
Regards,
-r.
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