%% You should probably cite draft-ietf-softwire-yang instead of this I-D.
@techreport{sun-softwire-yang-04,
    number =    {draft-sun-softwire-yang-04},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-sun-softwire-yang/04/},
    author =    {Qi Sun and Hao Wang and Yong Cui and Ian Farrer and Mohamed Boucadair and Rajiv Asati},
    title =     {{YANG Data Model for IPv4-in-IPv6 Softwire}},
    pagetotal = 35,
    year =      2015,
    month =     oct,
    day =       7,
    abstract =  {This document defines a YANG data model for the configuration and management of IPv4-in-IPv6 Softwire Border Routers and Customer Premises Equipment. It covers the Lightweight 4over6, MAP-E and MAP-T Softwire mechanisms.},
}