The bridge can also be used to block all non-IP traffic. A flag on each member interface specifies whether it should allow non-IP traffic to be passed in or out based on the protocol field in the ethernet header. This allows frames to be blocked when they cannot be filtered by the Layer-3 mechanisms provided so that tunnels through other protocols cannot be created. The only protocols allowed through an interface with this flag are the protocols necessary for IP to function: IPv4, IPv6, ARP, and RARP.