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Comment by Sebb767 | Hacker News Reader

This needs a (2019) added, or maybe a link directly to the newer posts.

Its still true though my public IP is 157.x.x.x while behind NAT it's 25.x.x.x

25.x is assigned to UK defence ministry as per the thread. Any ideas?

There aren't enough private IPv4 addresses for large(ish) mobile networks to address all their customers devices. Some networks work around this by using public v4 addresses which simply aren't in use. The UK DOD's block has never been publicly advertised (AFAIK) so they decided it was a "safe" block to use for this purpose. This isn't a new practice - I remember seeing Sprint doing this same thing many years ago.

The "correct" way to handle this would be to reuse real private IPv4 addresses within your network by segmenting it somehow, or do what some networks have done (T-Mobile US is probably the biggest) - use IPv6 with NAT64. That lets them forego internal IPv4 entirely and only use it at the edge for NAT.

So if UK DOD chooses to publicly advertise someday my Internet will break.

Good to know.

No, you just would not be able to reach UK DOD.

That's the best case scenario, considering that most customers probably don't need to connect to UK DOD. With the way IPv4 shortages are going, the more likely scenario is that some cloud provider/cdn buys that range, and sites start breaking randomly for customers.

Or whoever they transfer their address space to, if they try to be more socially responsible, which might end up being the next cool startup.

That would be socially irresponsible. Use IPv6.

I suspect major cloud providers may well end up buying the address space if it were to become available, so quite a few companies' services may not be reachable.

Perhaps. They sold a block to Microsoft to host O365 and Azure AD components a few years ago!

On reconnection got a 56.x ip so USPS as well.

25.* is not larger than 10.*. What problem does this solve?

Maybe not having to field tech support calls if their choice of private IP space conflicts with a customers choice?

They probably were already using 10 for something else when they decided to use 25.

Is there a list or some way to discover which blocks are like this that aren't in use?

https://bgp.potaroo.net/ipv4-stats/prefixes_unadv_pool.txt

Is this complete? All of 4.0/8 10.0/8 12.0/8 15.0/8 16.0/8 17.0/8... are unrouted?

Edit(v2): Complete list of unrouted (per that list) /8s along with their IANA designation

0: IANA - Local Identification

4, 15, 16, 32, 40, 44: Administered by ARIN

10: IANA - Private Use

12: AT&T Bell Laboratories

17: Apple Computer Inc.

38: PSINet, Inc

53: Daimler AG

55: DoD Network Information Center

57: Administered by RIPE NCC

73: ARIN

126: APNIC

127: IANA - Loopback

214: US-DOD

224 to 239: Multicast

240 to 255: Future use

(designations from https://www.iana.org/assignments/ipv4-address-space/ipv4-add...)

> All of (...) 17.0/8... are unrouted?

Definitely not complete:

    apple.com.              1424    IN      A       17.172.224.47
    apple.com.              1424    IN      A       17.178.96.59
    apple.com.              1424    IN      A       17.142.160.59

Most of these are routed and in very active use. I have suballocations of large chunks from 12/8 and 38/8. People will be unhappy if you picked most of them.

73/8 is entirely owned by Comcast and used for customers. 44 is no longer a /8, but sold+split and half in active use by AWS.

25.x.x.x is not advertised globally, not announced with BGP, so they're using it as private IP space. This works because you will never connect to a 25.x.x.x IP. It's just NAT.

> you will never connect to a 25.x.x.x IP

Unless the UK decides to sell it. An IPv4 /8 is worth at least $250 million at the moment.

$250 million is pocket change to a nation state.

I own a /24 myself (it's routed), and would never sell it.

When you say owned, do you mean like a PI or legacy allocation?

Yes, it's a legacy allocation from the early 90's. It predates ARIN.

I've seen 26.x.x.x get used as well for the same reasons. (US Department of Defense)

Why?

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