DNS filter
You can apply DNS category filtering to control user access to web resources. You can customize the default profile, or create your own to manage network user access and apply it to a firewall policy, or you can add it to a DNS server on a FortiGate interface. For more information about configuring DNS, see DNS. In FortiOS 6.4, the DNS proxy daemon handles the DNS filter in flow and proxy mode policies.
DNS filtering has the following features:
- FortiGuard Filtering: filters the DNS request based on the FortiGuard domain rating.
- Botnet C&C domain blocking: blocks the DNS request for the known botnet C&C domains.
- External dynamic category domain filtering: allows you to define your own domain category.
- DNS safe search: enforces Google, Bing, and YouTube safe addresses for parental controls.
- Local domain filter: allows you to define your own domain list to block or allow.
- External IP block list: allows you to define an IP block list to block resolved IPs that match this list.
- DNS translation: maps the resolved result to another IP that you define.
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Some DNS filter features require a subscription to FortiGuard Web Filtering. |
DNS filtering connects to the FortiGuard secure DNS server over anycast by default. For more information about this configuration, see DNS over TLS.
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DNS filter profiles cannot be used in firewall policies when the FortiGate is in NGFW policy-based mode; see Profile-based NGFW vs policy-based NGFW for more information. They can be used in the DNS server; see FortiGate DNS server for more information. |
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A DNS filter profile can be applied in a policy to scan DNS traffic traversing the FortiGate (see Configuring a DNS filter profile), or applied on the DNS server interface (see Applying DNS filter to FortiGate DNS server). |
DNS filter behavior in proxy mode
In cases where the DNS proxy daemon handles the DNS filter and if DNS caching is enabled (this is the default setting), then the FortiGate will respond to subsequent DNS queries using the result in the DNS cache and will not forward these queries to a real DNS server.
There are two options to disable this behavior:
- Disable DNS caching globally.
- Remove the DNS filter profile from the proxy mode firewall policy or from the DNS server configured on a FortiGate interface.
To disable DNS caching globally:
config system dns
set dns-cache-limit 0
end
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There will be a performance impact to DNS queries since each query will not be cached, and will be forwarded to a real DNS server. |
The following topics provide information about DNS filters: