pseudo MAC address (PMAC)

Pseudo MAC addresses (PMAC) are MAC addresses or IP addresses that are generated from a MAC address for a specific purpose and converted back to the previous address structure after use. Converting an IP address to a pseudo-MAC address can be used in IP multicast, it can be used to reduce the size of the address or for faster address retrieval in mapping tables.

1. IP multicast works with multicast addresses consisting of IP addresses and pseudo MAC addresses assigned to multicast groups. In IP multicast, the pseudo MAC addresses have the address space 01-00-5e-00-00 to 01-00-5e-7f-ff-ff.
2. In large networks with many thousands of nodes, the management of the mapping tables of Layer 2 switches reaches its limits because the processors with large L1 caches for MAC address management become very costly. Therefore, such networks are not designed as Layer 2 networks, but work with Layer 3 switches whose management is based on IP addresses. This is costly but feasible. Since switches recognize their position in the network by means of discovery, they can assign their own dummy addresses, the pseudo MAC addresses, to all servers surrounding them. These can be much smaller than the MAC addresses and used for internal forwarding of data packets to the next router. The server converts the received pseudo MAC addresses back into normal MAC addresses.