n/dns.md: add links to Wikipedia on ECS, Client-Subnet, fix link for DHCPv6 PD, link to PrivacyGuides DNS Overview as well

n/dns.md

@@ -65,8 +65,11 @@ least temporary. Thus I think this list belongs here close enough.
 
 ## What is ECS?
 
-EDNS Client-Subnet is a DNS extension letting the authoritative nameserver
-know your `/24` (IPv4) or `/56` (IPv6).
+[EDNS](https://en.m.wikipedia.org/wiki/Extension_Mechanisms_for_DNS) [Client-Subnet](https://en.wikipedia.org/wiki/EDNS_Client_Subnet) is a DNS extension letting the authoritative nameserver
+know your subnet, generally a `/24` (IPv4) or a `/56` (IPv6), but the revealed
+subnet size is up to your DNS resolver configuration.
+
+_See also simpler explanation at [PrivacyGuides.org DNS Overview](https://www.privacyguides.org/en/advanced/dns-overview/#what-is-edns-client-subnet-ecs)._
 
 - /24 is the first three parts of your IPv4 address e.g. 192.0.2.xxx.
   The last part of your IP address (the xxx) again is a number between 1
@@ -82,6 +85,7 @@ know your `/24` (IPv4) or `/56` (IPv6).
     which is the most common way of getting IPv6 address in your local area
     network as opposed to IPv4 where you would have
     [Dynamic Host Configuration Protocol (DHCP)](https://en.m.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol).
+    - Your router does get the IPv6 subnet assignment for LAN distribution by means of [DHCPv6 Prefix Delegation](https://en.m.wikipedia.org/wiki/Prefix_delegation) which is also common on mobile networks.
 
 ### Why to use ECS?
 
@@ -96,7 +100,7 @@ _Android DoH3 option:_ `dns.google`
 
 - [Green Code](https://www.exove.com/green-code/) ([pdf](https://www.exove.com/app/uploads/2023/09/Green-Code-v2.pdf) [txt](https://www.exove.com/app/uploads/2023/09/greencode-v2.txt))
 
-If you utilize services of internet giants or condent delivery networks, ECS will likely give you [the shortest distance, the lowest latency, the highest speed](https://en.m.wikipedia.org/wiki/Edge_computing) and may help with decreasing your _digital carbon footprint_.
+If you utilize services of internet giants or content delivery networks, ECS will likely give you [the shortest distance, the lowest latency, the highest speed](https://en.m.wikipedia.org/wiki/Edge_computing) and may help with decreasing your _digital carbon footprint_.
 
 If those matter to you, you may also like to consider [increasing your minimum TTL to around an hour in a local server](https://blog.apnic.net/2019/11/12/stop-using-ridiculously-low-dns-ttls/).
 
@@ -206,13 +210,19 @@ These issues bring additional questions:
 Or what is being sent to the authoritative servers.
 
 ```bash
+# https://support.google.com/interconnect/answer/7658602
 dig +short TXT o-o.myaddr.l.google.com.
+# https://www.akamai.com/blog/developers/introducing-new-whoami-tool-dns-resolver-information
 dig +short TXT whoami.ds.akahelp.net.
 dig +short TXT whoami.ipv6.akahelp.net.
 dig +short TXT whoami.ipv4.akahelp.net.
+# https://powerdns.org/useful-names/
+dig +short TXT whoami-ecs.lua.powerdns.org.
+dig +short TXT whoami-ecs.v6.powerdns.org.
+dig +short TXT whoami-ecs.v4.powerdns.org.
 ```
 
-- Note: Cloudflare sends ECS only for `whoami.ds.akahelp.net`, nowhere else.
+- Note: [Cloudflare sends ECS only for `whoami.ds.akahelp.net`, nowhere else](https://developers.cloudflare.com/1.1.1.1/faq/#does-1.1.1.1-send-edns-client-subnet-header).
 
 ---