@misc{rfc4891,
    series =    {Request for Comments},
    number =    4891,
    howpublished =  {RFC 4891},
    publisher = {RFC Editor},
    doi =       {10.17487/RFC4891},
    url =       {https://www.rfc-editor.org/info/rfc4891},
    author =    {Mohan Parthasarathy and Richard F. Graveman and Hannes Tschofenig and Pekka Savola},
    title =     {{Using IPsec to Secure IPv6-in-IPv4 Tunnels}},
    pagetotal = 23,
    year =      2007,
    month =     may,
    abstract =  {This document gives guidance on securing manually configured IPv6-in- IPv4 tunnels using IPsec in transport mode. No additional protocol extensions are described beyond those available with the IPsec framework. This memo provides information for the Internet community.},
}