A packet processor may implement programmable tunnel creation. A network packet may be received at a packet processor. A tunneling protocol may be identified for the network packet. The packet processor may access one or more memories to obtain tunnel header data that includes a tunnel header and field identifiers which indicate respective fields in the tunnel header that are determined based on data in the network packet. The tunnel header data may have been stored in the one or more memories prior to receiving the network packet. The network packet may be modified to insert the tunnel header into the network packet including the respective fields indicated by the field identifiers. The modified packet may then be transmitted.