They won't change the MAC addresses. Routers will, in a process called 'Frame Rewrite'By reading the source address of every frame that arrives, the switch builds a table that maps each MAC to the one port it lives behind, and from then on it forwards traffic to that single port instead of all of them. That table, how it fills, how it ages, and what the switch does when an address. A switch can learn MAC addresses in two ways: statically or dynamically. If PC1 sends an Ethernet frame to Switch1 which forwards the frame to Switch2 which in turn forwards the frame to PC2, does any decapsulation. Do Routers Change the MAC Address of Packets When Forwarding? 1. Introduction Media Access Control (MAC) addresses are unique identifiers to facilitate communications on physical network segments for Network interface cards (NICs).