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A comment on I spent a week without IPv4 (2023). Parent comment

Re:I spent a week without IPv4 (2023) by ck2 on Saturday December 20, 2025 @03:16PM (#46339216)
my tmobile 5g modem has ipv4 but changes ip every single page load, it's wild

I'm used to cablemodems with static ipv4 for months basically until mac changes

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Re:I spent a week without IPv4 (2023) by throw0101c on Saturday December 20, 2025 @03:20PM (#46339257)
Is it per chance 100.64.0.0/10?

* https://en.wikipedia.org/wiki/IPv4_shared_address_space

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Re:I spent a week without IPv4 (2023) by WarOnPrivacy on Saturday December 20, 2025 @04:36PM (#46339856)
It could be 21.0/8

ref:https://old.reddit.com/r/tmobileisp/comments/1gg7361/why_is_...

I booted an LTE router using a T-Mobile SIM.

Within an hour I had changed WAN IP. Both were from AS749 US-DOD NIC

    in 33.79.135.0/24 & 21.140.100.0/24.
They were cgnat'd behind TMble's advertised asn.
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Re:I spent a week without IPv4 (2023) by hylaride on Saturday December 20, 2025 @04:25PM (#46339768)
> my tmobile 5g modem has ipv4 but changes ip every single page load, it's wild

They're probably using CG-NAT, though IP changes that often is a bit aggressive.

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Re:I spent a week without IPv4 (2023) by WarOnPrivacy on Saturday December 20, 2025 @05:42PM (#46340339)
> They're probably using CG-NAT, though IP changes that often is a bit aggressive.

TMobile uses IPv4 addys in DOD's address space. They do change unexpectedly often.

And yeah. Being DOD IPs, they're cgnat'd behind tmobile's public ASN.

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Re:I spent a week without IPv4 (2023) by immibis on Saturday December 20, 2025 @07:07PM (#46340945)
Your IPv4 packets are getting tunneled to a CGNAT server which has an IP address pool.

Your website will load faster on cellphones if it supports IPv6. This is because the packets take more direct routes (because they don't go to the central CGNAT server) and because less processing is applied to them. Almost all mobile networks are now IPv6-only, with IPv4 traffic tunneled and CGNATted. Apparently T-Mobile is the rare exception.

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