%% You should probably cite rfc2003 instead of this I-D.
@techreport{ietf-mobileip-ip4inip4-03,
    number =    {draft-ietf-mobileip-ip4inip4-03},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-ietf-mobileip-ip4inip4/03/},
    author =    {Charles E. Perkins},
    title =     {{IP Encapsulation within IP}},
    pagetotal = 14,
    year =      1996,
    month =     jun,
    day =       5,
    abstract =  {This document specifies a method by which an IP datagram may be encapsulated (carried as payload) within an IP datagram. {[}STANDARDS-TRACK{]}},
}