RFC 4891:Using IPsec to Secure IPv6-in-IPv4 Tunnel...
RFC-Ref

IETF Secretariat


Click on the red underlined text to get to the source

... Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license ...



Google
Web
RFC-Ref