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Domain Name System Filter concepts

With the release of FortiOS 5.4.0, users configure the Domain Name System (DNS) Filter security profile independent of the Web Filter security profile.

DNS-based web filtering

This feature is similar to the FortiGuard DNS web filtering available in FortiOS 5.2. You can configure DNS web filtering to allow, block, or monitor access to web content according to FortiGuard categories. When DNS web filtering is enabled, your FortiGate must use the FortiGuard DNS service for DNS lookups. DNS lookup requests sent to the FortiGuard DNS service return with an IP address and a domain rating that includes the FortiGuard category of the web page.

If that FortiGuard category is set to block, the result of the DNS lookup is not returned to the requester. If the category is set to redirect, then the address returned to the requester points at a FortiGuard redirect page.

You can also allow access or monitor access based on FortiGuard category.

Blocking DNS requests to known Botnet C&C addresses

A new FortiGuard database contains a list of known Botnet C&C addresses. This database is updated dynamically and stored on the FortiGate. This database is covered by FortiGuard web filter licensing, so you must have a FortiGuard web filtering license to use this feature.

When you block DNS requests to known Botnet C&C addresses, using IPS, DNS lookups are checked against the Botnet C&C database. All matching DNS lookups are blocked. Matching uses a reverse prefix match, so all sub-domains are also blocked.

To enable blocking of DNS requests to known Botnet C&C addresses, go to Security Profiles > DNS Filter, and enable Block DNS requests to known botnet C&C.

Static URL filter

The DNS inspection profile static URL filter allows you to block, exempt, or monitor DNS requests by using IPS to look inside DNS packets and match the domain being looked up with the domains on the static URL filter list. If there is a match the DNS request can be blocked, exempted, monitored, or allowed.

If blocked, the DNS request is blocked and so the user cannot look up the address and connect to the site.

If exempted, access to the site is allowed even if another method is used to block it.

CLI commands

Rename webfilter-sdns-server-ip and webfilter-sdns-server-port:

config system fortiguard

set sdns-server-ip x.x.x.x

set sdns-server-port 53

end

Configure DNS URL filter:

config dnsfilter urlfilter

edit 1

set name "url1"

set comment ''

config entries

edit 1

set url "www.google.com"

set type simple

set action block

set status enable

edit 2

set url "www.yahoo.com"

set type simple

set action monitor

set status enable

edit 3

set url "www.foritnet.com"

set type simple

set action allow

set status enable

end

Configure DNS filter profile:

config dnsfilter profile

edit "dns_profile1"

set comment ''

config urlfilter

set urlfilter-table 1

end

config ftgd-dns

config filters

edit 1

set category 49

set action block

set log enable

edit 2

set category 71

set action monitor

set log enable

end

set log-all-url disable

set block-action redirect

set redirect-portal 0.0.0.0

set block-botnet enable

end

Configure DNS profile in a firewall policy:

config firewall policy

edit 1

set srcintf "any"

set dstintf "any"

set srcaddr "all"

set dstaddr "all"

set action accept

set schedule "always"

set service "FTP"

set utm-status enable

set dnsfilter-profile "dns_profile1"

set profile-protocol-options "default"

set nat enable

end

Configure DNS profile in profile group:

config firewall profile-group

edit "pgrp1"

set dnsfilter-profile "dns_profile1"

set profile-protocol-options "default"

end