Packet forwarding

Routing

Enable IP forward

Linux

sudo sysctl net.ipv4.ip_forward=1

Bridging

Enable promiscuous mode

By enabling this, packets with destination MAC address different from the NIC's will not be dropped by the NIC.

This feature requires NIC and its driver's support. For network adapters provided VirtualBox, promiscuous mode should be configured as "Allow All".

Linux

sudo ip link set dev {interface} promisc on

References

1. Packet forwarding