Add IP-AAAA-NODATA description

Signed-off-by: DL6ER <dl6er@dl6er.de>

docs/ftldns/blockingmode.md

@@ -21,6 +21,31 @@ doubleclick.net.        2       IN      AAAA    fda2:2001:4756:0:ab27:beff:ef37:
 ##### Advantage
 - Shows blocking page from which blocked webpages can be whitelisted
 
+##### Disadvantages
+- Requires a webserver to run on your Pi-hole
+- May cause time-outs for HTTPS content even with properly configured firewall rules
+- May cause problems with alternating prefixes on IPv6 addresses (see `IP-AAAA-NODATA`)
+
+## Pi-hole's IPv6 NODATA blocking
+`/etc/pihole/pihole-FTL.conf` setting:
+```
+BLOCKINGMODE=IP-AAAA-NODATA
+```
+
+Queries will be answered with the local IP addresses of your Pi-hole (as configured in your `setupVars.conf` file)
+```
+;; QUESTION SECTION:
+;doubleclick.net.               IN      ANY
+
+;; ANSWER SECTION:
+doubleclick.net.        2       IN      A       192.168.2.11
+doubleclick.net.        2       IN      AAAA    fda2:2001:4756:0:ab27:beff:ef37:4242
+```
+
+##### Advantage
+- Shows blocking page from which blocked webpages can be whitelisted
+- Serves IPv4-only replies and hence mitigates issues with rotating IPv6 prefixes
+
 ##### Disadvantages
 - Requires a webserver to run on your Pi-hole
 - May cause time-outs for HTTPS content even with properly configured firewall rules

docs/ftldns/configfile.md

@@ -72,9 +72,9 @@ Which privacy level is used?
 Should `FTL` ignore queries coming from the local machine?
 
 ### BLOCKINGMODE
-`BLOCKINGMODE=IP|NXDOMAIN`
+`BLOCKINGMODE=IP|IP-AAAA-NODATA|NXDOMAIN|NULL`
 
-Should `FTL` reply queries to blocked domains with IPs or `NXDOMAIN`?
+How should `FTL` reply to blocked queries?
 
 **[More details](blockingmode.md)**