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DNS Tracing


Notes:

The -s . (dash s dot) tells dnstracer to start the query from the root servers. The -c option tells dnstracer to ignore cached data.

Whenever an entry is not cached the search begins with the root servers.

# dnstracer -s. -c developer.ibm.com
Tracing to developer.ibm.com via A.ROOT-SERVERS.NET, timeout 15 seconds
A.ROOT-SERVERS.NET [.] (198.41.0.4)
|\___ M.GTLD-SERVERS.NET [com] (192.55.83.30)
| |\___ ns.austin.ibm.com [ibm.com] (192.35.232.34)
| |\___ ns.almaden.ibm.com [ibm.com] (198.4.83.35)
| | |\___ ns.watson.ibm.com [developer.ibm.com] (129.34.20.80)
| | \___ ns.austin.ibm.com [developer.ibm.com] (192.35.232.34)
| |\___ ns.ers.ibm.com [ibm.com] (204.146.173.35)
| | |\___ ns.watson.ibm.com [developer.ibm.com] (129.34.20.80)
| | \___ ns.austin.ibm.com [developer.ibm.com] (192.35.232.34)
| |\___ ns.watson.ibm.com [ibm.com] (129.34.20.80)
| \___ internet-server.zurich.ibm.com [ibm.com] (195.176.20.204)
| |\___ ns.watson.ibm.com [developer.ibm.com] (129.34.20.80)
| \___ ns.austin.ibm.com [developer.ibm.com] (192.35.232.34)
...

In this example we can clearly see that ns.almaden.ibm.com delegates the request to ns.watson.ibm.com or ns.austin.ibm.com for resolution. Large companies, or companies with more than one site will often delegate zones of authority in this manner. Though we also see that the root server knew to query ns.austin.ibm.com directly anyway.