tcsim comes with a set of include files that provide building blocks for configurations. For convenience, packet.def and ports.tc (from tcc, see section 2.13.4) are automatically included by default. Section 6.1.1 describes how this can be disabled.
The file packet.def contains macros for constructing IPv4 packets, with various transport layer protocols (TCP, UDP, ICMP, etc.). The actual content of packet.def is in the files packet4.def and packet6.def, which are included by packet.def, and should not be included individually.
ip.def is the predecessor of packet.def. While still extensively used in regression tests and examples, ip.def is obsolete and should be avoided in new configuration scripts.
The file tcngreg.def is only used internally by the tcng package for regression tests.
tcsim include files are normally installed in the directory /usr/lib/tcng/include/