ip.bieringer.net

Carrier Grade NAT (CGN) Test Page

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In case you see only (parts of) one square filling in the IPv4 2D source port distribution and dots are changing colors to yellow/red, yellow/red lines in the histogram and the port reusage > 0%, your system is probably behind a Carrier-Grade NAT device.
Warnings:
During execution, browser window is blocked for at least shown estimated time
Unexpected behavior may occur when used via proxy or from a mobile device

This page requires JavaScript enabled!

Control	Amount of connections to use for test: for test use 8, for analysis 1024/2048 is a good choice
Workflow step
Time [s] Consumed/Left
Protocol	IPv4	IPv6
Status
Info
Address Port
Port Counter
Address Counter
Port Min/Max/Delta/Reusage
2D Source Port distribution each dot refers to one source port same port used a 2nd time same port used >= 3 times
Histogram each x covers 256 ports each y-dot covers up to 16 hits and above 256 hits as y-dot a line shows an overflow

Update of graphics every ms and status every ms (supported browser: 'Firefox/Seamonkey', there are known but unresolved issues at least with IE11/Windows 8 and Edge/Linux).

How it works using Javascript in local browser:

A sequence of requests are made by browser using 'XMLHttpRequest' to a page returning client IP and port for IPv4 and IPv6
Relation of delta of seen min/max port to amount of ports plus distribution and histogram will show whether Carrier Grade NAT is probably active or not
Examples:

Graphics from a native IPv4/IPv6 Internet access provided by M-net using FritzBox and Windows 8 Client
Graphics from a MAC OS X client behind active Carrier Grade NAT
Graphics from an Ubuntu client behind active Carrier Grade NAT (ISP M-net)
Opera Mini on a Nokia E90 shows random port selection (no screenshot possible)

Using Linux you can simulate the behavior of CGN using e.g. on the host itself by reducing source port range to 256 ports only:

# sysctl -w net.ipv4.ip_local_port_range="32768 33023" (don't forget to reset after the test...)