Sindarina, Edge Case DetectiveJan 16, 2023

Since I just saw yet another developer use '1.2.3.4' in an example configuration, a reminder that you MUST NOT use publicly routable addresses that you do not control in your code.

Instead, use one of the available 'TEST-NET' IPv4 or IPv6 ranges documented in RFC 6890, such as;

192.0.2.0/24
198.51.100.0/24
203.0.113.0/24

❌ 1.2.3.4
✅ 192.0.2.4

Pass it on to all of your fellow developers, documentation writers, and so forth.

Full RFC is here;

https://datatracker.ietf.org/doc/rfc6890/

RFC 6890: Special-Purpose IP Address Registries

This memo reiterates the assignment of an IPv4 address block (192.0.0.0/24) to IANA. It also instructs IANA to restructure its IPv4 and IPv6 Special-Purpose Address Registries. Upon restructuring, the aforementioned registries will record all special-purpose address blocks, maintaining a common set of information regarding each address block.

IETF Datatracker
Show threadRichard WeltyJan 16, 2023
@sindarina back when i was teaching the networking class at UAlbany, i made it a point to cover this sort of stuff early on in the semester. it's pretty easy to miss learning it in an ad hoc, self taught network engineer career.
Show threadRichard WeltyJan 16, 2023
@sindarina back around 1999-2000, i ran engineering at a network management business. we took over a modest sized frame relay WAN for a department store chain, and discovered that they had arbitrarily chosen a particular network, which happened to be assigned to someone else. the good news is that it wasn't anyone they needed to interact with. the bad news is that it happened at all.
Show threadSindarina, Edge Case DetectiveJan 16, 2023
@nfgusedautoparts Yeah, I've had this happen as well. Renumbering a network is a hassle, it eventually got resolved when they moved to a new location, and we forced the issue by just folding the extra downtime into the planned time for the move 😄
Show threadRichard Welty
@sindarina i also recall that when GE Research set up their internal IP network back before they got a "real" internet connection, a particular staff member had just finished the hitchhiker's guide, so he picked class A network 42.
it turned out that this was taken (not really a surprise). so they had to renumber the whole facility into 3/8.
GE has since given up 3/8 and renumbered into private space corporation wide.
Jan 16, 2023 at 10:54pmWeb
Show threadSindarina, Edge Case DetectiveJan 16, 2023

@nfgusedautoparts Yeah, there's an increasing number of original Class A owners that have released their initial allocations. I think Halliburton's (38/8?) is on the market.

Apple did good holding on to theirs, though, unlike Microsoft they have zero issues doing allocations for their cloud infra nowadays.

Show threadRichard WeltyJan 16, 2023
@sindarina i remember that particular period, before CIDR when the expansion of the intertubz was still new to many of us and we had no concept of IPv4 space as an exhaustable resource. we started an offsite satellite of GE Research and i got a class C from SRI-NIC in 1992, but then PSI (one of the shiny new ISPs) went and got us a B that we didn't come close to needing, then or ever.