OpenSRS rate-limits WHOIS lookups to keep the WHOIS server available to legitimate registrars while preventing scraping and other abuse. This article describes the default limits applied on port 43, the error messages you may see when a limit is hit, and how to escalate when a legitimate IP range is blocked.
About WHOIS rate limiting
WHOIS (the Who Is protocol, port 43) is the public service registrars use to look up domain registration data. Because WHOIS data is sensitive and easy to harvest in bulk, OpenSRS applies both per-second and per-day limits to incoming queries.
Access limits for port 43 WHOIS
The default rate limits for each IP address or IP range are:
Limit type | Default value | Notes |
|---|---|---|
Per-second | 1 lookup per second | Applied per IP or IP range. |
Per-day | Configured per IP/range | Default daily limit is set per account/IP. Contact OpenSRS Support to confirm the daily rate-limit applied to your IP. |
Note: Per-second and per-day limits exist to ensure system stability and load management while still allowing registrars to perform the daily lookups they need to process transfers and other legitimate operations.
Warning: Specific daily limit values are not published in this article. If you require a documented value for your integration, confirm with OpenSRS Support and update this article.
WHOIS rate limit error messages
Message | What it means | What to do |
|---|---|---|
Maximum daily connection limit reached. Lookup refused. | The IP address making the query has reached its daily maximum for WHOIS server communication. | Reduce lookup volume from this IP, or contact OpenSRS Support if you believe the limit was hit in error. |
WHOIS lookup refused for this IP range. This IP range is on the OpenSRS block-list for WHOIS lookups. To request that this IP range be removed from the block-list, please send an email to whoisblock@tucows.com. | The IP range has been blocked because it was identified as abusing the WHOIS server. | Send an email to whoisblock@tucows.com with the IP range and a justification for removal. OpenSRS will investigate but does not guarantee removal from the block-list. |
Tip: If you operate from a shared NAT or a hosting provider's IP space, an apparent block may actually be caused by another tenant on the same IP range. Include that context in your removal request.
Next steps
- Throttle your client. Make sure your WHOIS client respects the 1 query/second per-IP limit and back-off on rate-limit responses.
- Distribute lookups responsibly. Avoid bursty lookup patterns that look like scraping; spread queries over the day.
- If blocked, escalate properly. Email whoisblock@tucows.com with the IP range and a clear business justification, and copy OpenSRS Support if the issue is blocking a transfer.
Questions? Contact OpenSRS Support.
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