Merge pull request #110 from lidel/add-dnslink-via-subdomain

docs: add section about DNSLink via Subdomain

Author: Mr0grog

content/guides/concepts/dnslink.md

@@ -5,9 +5,15 @@ menu:
         parent: concepts
 ---
 
-DNSLink uses DNS records to map a domain name (like `ipfs.io`) to an IPFS address. Because you can edit your DNS records, you can use them to always point to the latest version of an object in IPFS (remember that an IPFS object’s address changes if you modify the object). Because DNSLink uses DNS records, the names it produces are also usually easy to type and read.
+DNSLink uses [DNS TXT](https://en.wikipedia.org/wiki/TXT_record) records to map
+a domain name (like `ipfs.io`) to an IPFS address. Because you can edit your
+DNS records, you can use them to always point to the latest version of an
+object in IPFS (remember that an IPFS object’s address changes if you modify
+the object). Because DNSLink uses DNS records, the names it produces are also
+usually easy to type and read.
 
-A DNSLink address looks like an [IPNS](/concepts/ipns) address, but it uses a domain name in place of a hashed public key:
+A DNSLink address looks like an [IPNS](/guides/concepts/ipns) address, but it
+uses a domain name in place of a hashed public key:
 
 ```
 /ipns/ipfs.io
@@ -25,9 +31,9 @@ When an IPFS client or node attempts to resolve that address, it looks for a `TX
 dnslink=/ipfs/<CID for your content here>
 ```
 
-For example, if you look up ipfs.io’s DNS records, you’ll see its DNSLink entry (see “answer section” at the bottom):
+For example, if you look up `ipfs.io`’s DNS records, you’ll see its DNSLink entry:
 
-```
+```sh
 $ dig +noall +answer TXT ipfs.io
 ipfs.io.		59	IN	TXT	"dnslink=/ipfs/QmYNQJoKGNHTpPxCBPh9KkDpaExgd2duMa3aF6ytMpHdao"
 ```
@@ -43,3 +49,24 @@ Will get you this block:
 ```
 /ipfs/QmYNQJoKGNHTpPxCBPh9KkDpaExgd2duMa3aF6ytMpHdao/media/
 ```
+
+
+## Publishing via a Subdomain
+
+You can also publish DNSLink records using a special subdomain named `_dnslink`. This is useful when you want to improve the security of an automated setup or delegate control over your DNSLink records to a third-party without giving away full control over the original DNS zone.
+
+For example, [`docs.ipfs.io`](https://docs.ipfs.io) does not have a TXT record, but the page still loads
+because a TXT record exists for `_dnslink.docs.ipfs.io`:
+
+```sh
+$ dig +noall +answer TXT _dnslink.docs.ipfs.io
+_dnslink.docs.ipfs.io.  34  IN  TXT "dnslink=/ipfs/QmeveuwF5wWBSgUXLG6p1oxF3GKkgjEnhA6AAwHUoVsx6E"
+```
+
+<!-- TODO: Once IPNS is more reliable, describe combining it with DNSLink.
+### Linking to IPNS
+
+DNSLink can point at [IPNS](/guides/concepts/ipns) paths as well. IPNS path is
+a mutable pointer which  enables you to update your website by publishing
+to a PeerID without the need for updating TXT record every time hash changes.
+-->