How to use `dns-sd` to discover all domains with specific TLD?

Question

I'm trying to discover all domains with the TLD .ffhh. This is the TLD of the Freifunk Meshnetwork in Hamburg. I tried the following command in Mac Terminal:

dns-sd -B _http._tcp ffhh.

I get this output, but nothing happens after that:

Browsing for _http._tcp.ffhh. DATE: ---Thu 23 Jul 2015--- 10:40:20.934 ...STARTING...

I guess I'm using dns-sd wrong!? What would be the right command to discover all domains with this TLD?

Answer 1

I do not think you can use dns-sd to browse top level domains. (And if you really can -- I'm not sure about this! -- then your command would be correct. It just does not find any result for that TLD. See my further answer...)

Also, browsing for _http._tcp in a certain domain will only display results, if there actually is a HTTP service that is announced via DNS-SD in that domain.

1. dns-sd is for local. domain in the first place

To test it, you can run dns-sd -R in one terminal to announce a fake HTTP service:

 dns-sd  \
   -R "A Fake Announcement to Register a Dummy HTTP Server" \
   _http._tcp,_universal \
   .   \
   8081

and then check if the announcement appears in the local browse list:

 dns-sd -B _http._tcp

2. dns-sd works also for remote domains ... under certain conditions

To check for announced services in a remote domain, try:

 dns-sd -B _ftp._tcp dns-sd.org.

You should see something like

Browsing for _ftp._tcp.dns-sd.org.
DATE: ---Thu 19 May 2016---
17:40:02.111  ...STARTING...
Timestamp     A/R  Flags  if Domain        Service Type  Instance Name
17:40:02.112  Add      3   0 dns-sd.org.   _ftp._tcp.    Apple QuickTime Files
17:40:02.112  Add      3   0 dns-sd.org.   _ftp._tcp.    Microsoft Developer Files
17:40:02.112  Add      2   0 dns-sd.org.   _ftp._tcp.    Restricted, Registered Users Only
^C

Then you can resolve a specific instance by running another command:

dns-sd -L "Microsoft Developer Files" _ftp._tcp dns-sd.org.

  Lookup Microsoft Developer Files._ftp._tcp.dns-sd.org.
  DATE: ---Thu 19 May 2016---
  17:40:43.972  ...STARTING...
  17:40:44.365  Microsoft\032Developer\032Files._ftp._tcp.dns-sd.org. can be reached at ftp.microsoft.com.:21 (interface 0)
   txtvers=1
   path=/developer
^C

3. So why did browsing the remote dns-sd.org. domain work at all?

This is because Stuart Cheshire, the guy who "invented" DNS-SD and who runs the dns-sd.org domain, did register the FTP services in his own domain within his standard DNS server setup in with the appropriate means.

4. So why does dns-sd.org return records about a Microsoft-controlled FTP service?

This is because Stuart Chesire registered that FTP service as a "proxy advertisement"....

---

5. Why did your query for the fffh. top level domain not work?

Mainly, because that domain most likely didn't register within a standard DNS server all the HTTP services which are hosted within its realm.

Maybe it doesn't even run a DNS server at all within its domain.

You would only discover those HTTP servers via dns-sd -B _http._tcp local., if each webmaster of such a server would...

• ...run the appropriate dns-sd -R ... command in the background (if he has a Mac), or
• ...run the analog avahi-publish -s ... command (if he has Linux)

---

6. Additional Info

BTW, you could browse and discover remote services without specifying the remote domain name, if you added the remote domain in your general DNS configuration as a "browse domain". See this screenshot where I added dns-sd.org on a MacBook:

In this case you can simply run

dns-sd -B _http._tcp

to also get the remote HTTP services listed (as well as the local ones) instead of running

dns-sd -B _http._tcp dns-sd.org.