Twin directories of usdnr:

[DIR]  ftp://ftp.botik.ru/pub/doc/rfc/usdnr/
[DIR]  ftp://ftp.dlut.edu.cn/pub1/Documents/RFC/usdnr/
[DIR]  ftp://coombs.anu.edu.au/pub/rfc/usdnr/
[DIR]  ftp://ftp.stack.nl/pub/documents/usdnr/
[DIR]  ftp://ftp.sai.msu.su/pub/doc/rfc/usdnr/
[DIR]  ftp://ftp.kame.net/.mirror/ftp.isi.edu/in-notes/usdnr/
[DIR]  ftp://ftp.itojun.org/.mirror/ftp.ietf.org/rfc/usdnr/
[DIR]  ftp://ftp.mayn.de/pub/really_old_stuff/mirrors/RFC/usdnr/
[DIR]  ftp://ftp.mayn.de/pub/really_old_stuff/mirrors/ftp.isc.org/pub/rfc/usdnr/
[DIR]  ftp://ftp.iavsc.org/pub/misc/rfc/usdnr/
[DIR]  ftp://virtualhosts.botik.ru/pub/doc/rfc/usdnr/
[DIR]  ftp://95.129.137.164/pub/doc/rfc/usdnr/