Where the checks come from.
If you run an allowlist or read your access logs, this page is for you. Every request from up4 originates from the addresses below and says so in its user agent. New addresses are published here before they send a single check.
The current list.
| Region | Location | IPv4 | Status |
|---|---|---|---|
| eu | Germany · Falkenstein · Hetzner | 178.105.7.124 | active |
| eu | Germany · Frankfurt · UpCloud | 87.58.154.44 | active |
| us | United States · Chicago · UpCloud | 209.50.48.241 | active |
| asia | Singapore · UpCloud | 213.163.195.218 | active |
| au | Australia · Sydney · UpCloud | 212.147.252.34 | active |
Machine-readable: curl https://upfour.io/ips.txt — one address per line, nothing else.
Each address is listed here before it sends a check, and the region picker only offers
regions with a live checker. The region column matches the region you select per monitor.
Our probes introduce themselves.
up4-checker/1.0 (+https://upfour.io/ips) Every HTTP check carries this user agent, so an up4 probe is always attributable in your logs. If you set custom request headers on a monitor, your headers win — including a custom user agent.
Allowlisting guidance
- Allow by IP, not by user agent. A user-agent string is trivially spoofable; the addresses above are not.
- Do not rate-limit the addresses above if you monitor at 10-second intervals — the whole point is that we keep asking.
- Checks use
HEADwith aGETfallback by default; you can pin the method per monitor.
Change policy
Egress addresses are stable. When one is added or retired, this page and the status page say so before the change takes effect — an allowlist should never be the reason your monitoring looks down.