This RFC 7422 was published in 2014
In some instances, Service Providers (SPs) have a legal logging requirement to be able to map a subscriber's inside address with the address used on the public Internet (e.g., for abuse response).
Unfortunately, many logging solutions for Carrier-Grade NATs (CGNs) require active logging of dynamic translations.
CGN port assignments are often per connection, but they could optionally use port ranges.
Research indicates that per-connection logging is not scalable in many residential broadband services.
This document suggests a way to manage CGN translations in such a way as to significantly reduce the amount of logging required while providing traceability for abuse response.
IPv6 is, of course, the preferred solution.
While deployment is in progress, SPs are forced by business imperatives to maintain support for IPv4.
This note addresses the IPv4 part of the network when a CGN solution is in use.
RFC 7422 introduction
It is becoming increasingly difficult to obtain new IPv4 address assignments from Regional/Local Internet Registries due to depleting supplies of unallocated IPv4 address space.
To meet the growing demand for Internet connectivity from new subscribers, devices, and service types, some operators will be forced to share a single public IPv4 address among multiple subscribers using techniques such as Carrier-Grade NAT (CGN) [RFC6264] (e.g., NAT444 [NAT444], Dual-Stack Lite (DS-Lite) [RFC6333], NAT64 [RFC6146], etc.).
However, address sharing poses additional challenges to operators when considering how they manage service entitlement, public safety requests, or attack/abuse/fraud reports [RFC6269].
In order to identify a specific user associated with an IP address in response to such a request or for service entitlement, an operator will need to map a subscriber's internal source IP address and source port with the
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