/usr/include/freeradius/rfc6519.h is in libfreeradius-dev 3.0.12+dfsg-5+deb9u1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | /* AUTO-GENERATED HEADER FILE. DO NOT EDIT. */
#define PW_DS_LITE_TUNNEL_NAME 144
|