Alias sctp is part of the SONATA project to develop and release a BSD licensed implementation of a Network Address Translation (NAT) module that supports the Stream Control Transmission Protocol (SCTP). Arriving SCTP packets are first parsed for information that may be important to the association’s state in the NAT. This information along with the SCTP message is then passed to the state machine for further processing for a final decision on whether to NAT the packet, and whether the association’s state in the NAT should change. Alias sctp is implemented as a patch for the libalias kernel module, which works with the FreeBSD IPFW2 NAT module. Many of alias sctp’s parameters can be configured dynamically through the FreeBSD sysctl interface. Some minor modifications to the storage and management of IP addresses will need to be made when libalias supports IPv6. Alias sctp 0.2 is a fully functional IPv4 SCTP NAT.