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Old 2014-09-09, 19:01   #670
Serpentine Vermin Jar
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Jul 2014

63158 Posts

Originally Posted by chalsall View Post
A URL (or URI) is not (in and of itself) a domain (although it includes one) and thus can't be converted by the DNS system into an IP (which is what the ping targets).
Yeah, what you said.

Pinging works on the FQDN (fully qualified domain name), not a URI with the http, ftp, whatever.

I was a little hesitant at first to even allow ICMP through to the new server when I was setting up the firewall, but in the end I did because it is a pretty good troubleshooting tool to make sure you can "see" the server at all.

ICMP isn't as bad as it used to be when there were all kinds of ways you could attack it like the ping of death, etc.

Anyway, besides pinging, you can also do a plain "nslookup" to check that it's looking up the right address. It's not foolproof though because nslookup will always do a fresh query of DNS, but by doing a ping it will use any cached IP it has on your OS.

And then you can do more fun troubleshooting like (on Windows):
nslookup -type=any

And then you see that "www" is really just a cname to the @ record. And doing the same -type=any for just plain gets you the real deal, an A record to the IP address.

Your DNS client does the cname->A-record lookups automagically, but hey, maybe I just blew some people's minds with that info.
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