The given source file is licensed under the newer RFC license.
The majority of IETF documents, such as RFCs, are not licensed under DFSG-free terms, and should thus not be included in Debian main.
If this file is multi-licensed, please override the tag.
If this is a false-positive, please report a bug against Lintian.
Refer to https://wiki.debian.org/NonFreeIETFDocuments for details.