this post was submitted on 03 Aug 2025
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CGNAT version 2 (infosec.pub)
submitted 21 hours ago by Xylight@lemdro.id to c/programmer_humor@programming.dev
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[–] Kazumara@discuss.tchncs.de 13 points 12 hours ago (7 children)

Funny how many here took this to be real, judging from the reactions. To me it's an obvious joke.

Question to you guys: How do you suppose 200 million customers will share the less than 65'536 ports that are available on that one address?

[–] Fred@programming.dev 6 points 9 hours ago (2 children)

As @shane@feddit.nl says, you can use the same public port for many different destination address, vendors may call it something like "port overloading".

More importantly, you can install a large pool of public address on your CGNAT. For instance if you install a /20 pool, work with a 100 users / public address multiplexing, you can have 400,000 users on that CGNAT. 100 users / address is a comfortable ratio that will not affect most users. 1000 users / address would be pushing it, but I'm sure some ISP will try it.

If you search for "CGNAT datasheet" for products you can deploy today, the first couple of results:

[–] Kazumara@discuss.tchncs.de 3 points 9 hours ago (1 children)

As @shane@feddit.nl says, you can use the same public port for many different destination address, vendors may call it something like “port overloading”.

I just responded to him on that point, while you were typing to me. I didn't know this existed, thanks for pointing it out!

More importantly, you can install a large pool of public address on your CGNAT. For instance if you install a /20 pool, work with a 100 users / public address multiplexing, you can have 400,000 users on that CGNAT. 100 users / address is a comfortable ratio that will not affect most users. 1000 users / address would be pushing it, but I’m sure some ISP will try it.

Sure, yeah, I have seen a few threads on NANOG about the NAT address ratios people are using. I also think I remember someone saying he was forced to use 1000 and it kind of worked as long as he pulled the heaviest users out of the pool. But if I recall correctly he was also saying he made IPv6 available in parallel to reduce the CGNAT load.

But the point that made this post ridiculous and an obvious joke is that it said "one address" :-)

[–] Fred@programming.dev 1 points 8 hours ago

Well the "one address" bit sure :) but given the scale supported by CGNAT systems today, I don't think being able to support an entire country behind a single cluster is that far off. At which point the difficulty becomes "is the 100.64.0.0/10 block big enough"? Or maybe they're using DS-lite for the hauling from private network to the NAT.

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