Very strange how the very RFC that describes the protocol says otherwise.

https://tools.ietf.org/html/rfc6970

Internet Engineering Task Force (IETF) M. Boucadair Request for Comments: 6970 France Telecom Category: Standards Track R. Penno ISSN: 2070-1721 D. Wing Cisco July 2013

                 Universal Plug and Play (UPnP)

Internet Gateway Device - Port Control Protocol Interworking Function (IGD-PCP IWF)

Abstract

This document specifies the behavior of the Universal Plug and Play (UPnP) Internet Gateway Device - Port Control Protocol Interworking Function (IGD-PCP IWF). A UPnP IGD-PCP IWF is required to be embedded in Customer Premises (CP) routers to allow for transparent NAT control in environments where a UPnP IGD is used on the LAN side and PCP is used on the external side of the CP router.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6970.