Threat Level: green Handler on Duty: Rob VandenBrink

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RFC 6598 - Carrier Grade NAT

Three years ago Johannes published a diary on Reserved IP Address Space with a complete list of reserved IPv4 address that obviously included the well-known as well as some new one such as RFC 6598 (released in April 2012) "[...] to accommodate the needs of Carrier-Grade NAT (CGN) devices."[1] The address space reserved for CGN is which is used to counter the IPv4 address shortage by putting multiple hosts in a private subnet behind a public IP address.

Here is a simplified illustration of CGN:

If you are curious as to whether you carrier is using RFC 6598 CGN addresses, you can check your logs or traffic (packets) for


Guy Bruneau IPSS Inc.
Twitter: GuyBruneau
gbruneau at isc dot sans dot edu


523 Posts
ISC Handler
Feb 28th 2016

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