Making Use of 240/4 NetBlock

John R. Levine johnl at
Wed Mar 9 20:06:45 UTC 2022

> Um, are you suggesting there is sufficiently heavy use of 240/4 to 
> result in a significant security/stability issue if the address space is 
> allocated?  I thought you were arguing too many systems would have to be 
> updated to even send/receive packets with 240/4 in the source or 
> destination field.

Both, actually.  A few messages back someone said a cloud provider was 
using 240/4 for private address space, which is easy to believe since they 
have their own versions of the system software they run, e.g., Amazon's 
own distro of linux for use within AWS.

So first you have to figure out all of the random computers that need 
network stack upgrades, and then, oh, you can't talk to Google or whoever. 
At this point, either buying a chunk of real IPv4 space or getting IPv6 
working looks quite attractive.

John Levine, johnl at, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail.

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