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systemd'oh! DNS lib underscore bug bites everyone's favorite init tool, blanks Netflix

Gordon 11

It "is legal" but not in hostnames.

Which is the source of the problem.

The assumption in the original DNS was that an A record (although this is an AAAA, since the offending item appears to be IPv6) would point to a host.

This was always wrong - it only ever pointed to an interface (given that you can have multiple ones on a single host it clearly can't be a hostname), but the rule was built into the RFC IIRC).

So bind 4.x disallowed it.

The workaround was to set up a PTR records containing "_" to your A record, which contained "-" instead (since thy were aliases they could be "anything").

Then someone added a compilation option to allow "_" in A records. That must have been in the mid 90's.

Along came bind8 and made it a run-time option.

For someone to have got this wrong 20 years later is just a terrible piece of coding.

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