Work at the Emergency Location Task Group of NICC Standards Limited (the UK's telecoms industry standards body) prompted the addition of port number identifiers in HELD Identity to allow HELD requests for Devices that are behind NAT devices. Subsequent analysis has determined that in the presence of particular types of NAT devices, and in particular Carrier Grade NATs, it is necessary to know the complete tuple of (Layer 3 protocol, Layer 4 protocol, source address, source port, destination address, destination port) in order to unambiguously identify a flow, and subsequently the true Device. This document specifies an XML Schema and a URN Sub-Namespace for a Flow Identity Extension to support this requirement and provides a more generally applicable means of identifying a Device based on the parameters of a network flow of which it is an endpoint. Since the Location Recipient may not know in advance whether the Device is behind a NAT device, the port number elements from Section 3.3 of are deprecated and MUST NOT be used in new client implementations. Note that server implementations of this specification may still encounter requests formed by clients that have implemented only , and those requests might contain the deprecated port element. For implementation details not specified in this document, please refer to and .

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in . The terms "Device" and "Target" are used as defined in .

An example HELD request is shown below:

geodetic

192.0.2.25

1024

198.51.100.238

80 ]]> The ]]> element MUST contain: a "layer3" attribute with a value of "ipv4" or "ipv6". a "layer4" attribute with a value of "udp" , "tcp" , "sctp" , "dccp" , or a decimal integer representing any applicable protocol from the IANA Assigned Internet Protocol Numbers Registry. an ]]> element and a ]]> element whose child elements contain the Layer 3 address (which MUST conform to the relevant "IPv4address" or "IPv6address" grammar as defined in ) and the Layer 4 port number of each end of the flow. and MAY optionally contain: a "target" attribute with a value of "src" (default) or "dst" to indicate which end of the flow corresponds to the Target of the ]]> with respect to the HELD protocol.

HELD Flow Identity This document defines Flow Identity elements for HELD. ]]>

This section registers a new XML namespace, "urn:ietf:params:xml:ns:geopriv:held:flow", as per the guidelines in . URI: urn:ietf:params:xml:ns:geopriv:held:flow Registrant Contact: IETF GEOPRIV Working Group (geopriv@ietf.org), Ray Bellis (ray.bellis@nominet.org.uk) XML:

HELD Flow Identity Parameters

Namespace for HELD Flow Identity Parameters

urn:ietf:params:xml:ns:geopriv:held:flow

See RFC 6915.

END ]]>

This section registers an XML Schema as per the guidelines in . URI: urn:ietf:params:xml:ns:geopriv:held:flow Registrant Contact: IETF GEOPRIV Working Group (geopriv@ietf.org), Ray Bellis (ray.bellis@nominet.org.uk) Schema: The XML for this schema can be found as the entirety of of this document.

All of the considerations in apply to the use of the mechanism defined in this document. Like , this specification assumes that the Location Server being queried already has access to the internal state of the network near one end of the flow being queried (for instance, access to the bindings in a NAT in the path of the flow). Clients making queries using this specification in environments where that assumption may not be true should be aware that the request provides information about that client's communications that the Location Server would not otherwise be able to discern and may represent additional privacy exposure for that client.

This document introduces no new security considerations beyond those in .

The author wishes to thank the members of the NICC Emergency Location Task Group, the IETF GeoPriv Working Group, and the authors of , from which the text for the URN and XML Schema Registrations were derived.