Technical Tip: Configuring DNS safe search

[lestopace]

Description

Enable DNS Filter safe search so that FortiGate responds with the search engine's children and school safe domain or IP address.
Users might not be aware of this filter.
Explicit contents are filtered by the search engine itself.

This feature is not 100% accurate but it can help to avoid explicit and inappropriate search results.
This feature currently supports Google, Bing, and YouTube.

Related document.
https://docs.fortinet.com/document/fortigate/6.2.0/cookbook/12534/dns-safe-search

https://docs.fortinet.com/document/fortigate/7.4.0/administration-guide/12534/dns-safe-search

Solution
DNS safe search.

To configure DNS Filter Safe Search from GUI:
1) Go to Security Profiles -> DNS Filter and edit or create a DNS Filter.
2) Enable Enforce 'Safe search' on Google, Bing, YouTube.
3) For Restrict YouTube Access, select 'Strict' or 'Moderate'.

To configure DNS Filter Safe Search from CLI.

# config dnsfilter profile
    edit "demo"
        # config ftgd-dns
            set options error-allow
            config filters
                edit 2
                    set category 2
                next
               ...
            end
        end
        set log-all-domain enable
        set block-botnet enable
        set safe-search enable       <----- DNS Filter Safe Search option.
    next
end

Sample.

To see an example of how this works, enable this option.

From the internal network PC, use a command line tool such as 'dig' or 'nslookup' to do a DNS query on www.bing.com.

For example:

# dig www.bing.com
;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 46568
;; Flags: qr rd ra; QUERY: 1; ANSWER: 2; AUTHORITY: 0; ADDITIONAL: 0

;; QUESTION SECTION:
;; www.bing.com.                IN      A

;; ANSWER SECTION:
www.bing.com.           103     IN      CNAME   strict.bing.com.  <-----
strict.bing.com.        103     IN      A       204.79.197.220

;; Received 67 B
;; Time 2019-04-05 14:34:52 PDT
;; From 172.16.95.16@53(UDP) in 196.0 ms

The DNS query for www.bing.com returns with a CNAME strict.bing.com, and A record for the CNAME.

The user's web browser then connects to this address with the same search engine GUI but any explicit content search is filtered out.

Check the DNS Filter log for the message DNS Safe Search enforced.

To check the DNS Filter Safe Search log from CLI.

1: date=2019-04-05 time=14:34:53 logid="1501054804" type="utm" subtype="dns" eventtype="dns-response" level="notice" vd="vdom1" eventtime=1554500093 policyid=1 sessionid=65955 srcip=10.1.100.18 srcport=36575 srcintf="port10" srcintfrole="undefined" dstip=172.16.95.16 dstport=53 dstintf="port9" dstintfrole="undefined" proto=17 profile="demo" xid=59573 qname="www.bing.com" qtype="A" qtypeval=1 qclass="IN" ipaddr="204.79.197.220" msg="DNS Safe Search enforced" action="pass" sscname="strict.bing.com" cat=41 catdesc="Search Engines and Portals"

2: date=2019-04-05 time=14:34:53 logid="1500054000" type="utm" subtype="dns" eventtype="dns-query" level="information" vd="vdom1" eventtime=1554500092 policyid=1 sessionid=65955 srcip=10.1.100.18 srcport=36575 srcintf="port10" srcintfrole="undefined" dstip=172.16.95.16 dstport=53 dstintf="port9" dstintfrole="undefined" proto=17 profile="demo" xid=59573 qname="www.bing.com" qtype="A" qtypeval=1 qclass="IN"

To check the DNS Filter Safe Search on a Windows machine:

Safe Search Disabled:

Safe Search Enabled:

Additional information.

For each search engine's safe search specifications, see its specification page:
- https://help.bing.microsoft.com/#apex/18/en-US/10003/0
- https://support.google.com/websearch/answer/510?co=GENIE.Platform%3DDesktop&hl=en
- https://support.google.com/youtube/answer/174084?co=GENIE.Platform%3DDesktop&hl=en