%% You should probably cite draft-ietf-intarea-gre-mtu instead of this I-D.
@techreport{bonica-intarea-gre-mtu-00,
    number =    {draft-bonica-intarea-gre-mtu-00},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-bonica-intarea-gre-mtu/00/},
    author =    {Ron Bonica},
    title =     {{Generic Routing Encapsulation (GRE) Fragmentation Strategy}},
    pagetotal = 8,
    year =      2013,
    month =     may,
    day =       29,
    abstract =  {This memo documents a GRE fragmentation strategy upon which many vendors have converged. Specifically, it defines procedures to be executed by GRE ingress routers. It is published so that those building new implementations will be aware of best common practice. It is also published so that those building applications over GRE will understand how GRE works.},
}