Internet Filtering in Iran in Brief
Iran operates one of the most extensive internet filtering systems in the world. Social networks, many news sites, messaging apps and a long list of other services are filtered for users on Iranian networks. Like China, Iran combines several techniques, including DNS manipulation, HTTP and SNI filtering, IP blocking and bandwidth throttling during sensitive periods.
For a website owner outside Iran, the easiest layer to check is DNS. Our Iran Firewall Test does this in one step.
The Block-Page Address
When a domain is filtered at the DNS level, Iranian resolvers do not return the website’s real address. Instead they return an address that leads to a block page. In our own checks, the Iranian public resolver Shecan (178.22.122.100) answered well-known filtered domains such as facebook.com, twitter.com and bbc.com with 10.10.34.36, while unfiltered sites resolved to their normal public addresses.
10.10.34.36 belongs to the 10.0.0.0/8 private range defined in RFC 1918. Private addresses are not routable on the public internet, so a public website can never legitimately live there. When a resolver returns a private address for a public domain, it is a strong signal of filtering.
How the Iran Firewall Test Works
The tool queries two resolvers for the same domain:
- Google Public DNS (8.8.8.8) as the reference.
- Shecan (178.22.122.100), a public DNS service operated in Iran and widely used there. Shecan applies the national filtering rules, which makes it a practical reference for what users on Iranian networks see.
The answers are then classified:
- Blocked (DNS filtering detected): the Iranian resolver returned a private or otherwise non-routable address such as 10.10.34.36.
- Possibly blocked – no DNS answer: Google returned an address, the Iranian resolver returned nothing.
- Possibly blocked – answer points to another network: the Iranian answer belongs to an unrelated network.
- Not blocked at DNS level: the answers match or belong to the same network (normal for CDN-hosted sites).
Limits of a DNS Test
A single resolver is a sample, not the entire country. Individual ISPs can apply rules differently, and some blocking happens after DNS — for example by resetting HTTPS connections based on the requested hostname. A “not blocked at DNS level” result therefore means DNS is clean, not that every user in Iran can reach the site. If you need certainty, combine the DNS test with feedback from real users or measurement projects such as OONI, which collect tests run from inside the country.
Why Your Site Might Be Filtered
Filtering in Iran is not limited to political content. Sites can be filtered because of their category (for example social media or VPN services), because they share an IP address with a filtered site, or because they embed resources from a filtered domain. If you use shared hosting, check which other domains share your server with our Reverse IP Lookup.
Practical Tips
- Keep critical pages lightweight and avoid depending on third-party scripts that are themselves filtered.
- Re-test after moving to a new host or CDN, because the IP address change may affect IP-based filtering.
- Remember that sanctions and payment restrictions are a separate issue from filtering: a site can be reachable but still unable to accept payments from Iran.