Reverse DNS (PTR records)

Reverse DNS is the hostname someone gets when they ask "what's the name behind this IP?" — the inverse of normal DNS resolution. The records live in a separate tree (in-addr.arpa. for IPv4, ip6.arpa. for IPv6) and are authoritative for the IP block they cover.

For most VMs, the default reverse DNS (unused.nimbusnexus.net or similar) is fine. Set a custom PTR when:

You run a mail server. Most major email providers reject mail from IPs whose PTR doesn't match the sending hostname's forward DNS. Without a matching PTR, your delivery rate drops to zero.
You're allowlisted by a partner using PTR-based identification. Some firewalls do reverse-lookup-then-forward-lookup verification for inbound TCP.

PTR records are scoped to NimbusNexus-allocated floating IPs — you can't set PTRs on an IP that isn't ours.

What's next

Floating IPs — the IP allocations PTRs are set on.
DNS zones and DNS records — the forward-DNS side.

No endpoints to show

The OpenAPI spec doesn't currently expose any endpoints under thereverse-dnstag. This is usually a manifest typo; check that the tag matches what the backend serves at /openapi/external.json.

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