From: smb@research.att.com
Date: Wed, 11 Aug 93 09:52:20 PDT
To: jthomas@kolanut.mitre.org (Joe Thomas)
Subject: Re: Numeric IP address for ftp.eff.org?
Message-ID: <9308111649.AA06257@toad.com>
MIME-Version: 1.0
Content-Type: text/plain


	 Round Waffle wrote: 

	 But when you actually ftp to ftp.eff.org, the hostname reported is  
	 kragar.eff.org, and a traceroute there shows the endpoint's IP address
	 as  
	 192.88.144.4.  Creative DNS administration...

The dig output explains what's going on.

	$ dig ftp.eff.org

	; <<>> DiG 2.0 <<>> ftp.eff.org 
	;; ->>HEADER<<- opcode: QUERY , status: NOERROR, id: 6
	;; flags: qr aa rd ra ; Ques: 1, Ans: 2, Auth: 0, Addit: 0
	;; QUESTIONS: 
	;;      ftp.eff.org, type = A, class = IN

	;; ANSWERS:
	ftp.eff.org.    86400   CNAME   kragar.eff.org.
	kragar.eff.org. 86400   A       192.88.144.4

	;; Sent 1 pkts, answer found in time: 158 msec 
	;; FROM: inet to SERVER: default -- 0.0.0.0
	;; WHEN: Wed Aug 11 11:44:15 1993
	;; MSG SIZE  sent: 29  rcvd: 73

In other words, ftp.eff.org is an alias for the official name of
the host.  Quite properly, the inverse map lists the official name
for the host:

	$ dig -x 192.88.144.4

	; <<>> DiG 2.0 <<>> -x 
	;; ->>HEADER<<- opcode: QUERY , status: NOERROR, id: 6
	;; flags: qr aa rd ra ; Ques: 1, Ans: 1, Auth: 0, Addit: 0
	;; QUESTIONS: 
	;;      4.144.88.192.in-addr.arpa, type = ANY, class = IN

	;; ANSWERS:
	4.144.88.192.in-addr.arpa.      86400   PTR     kragar.eff.org.

	;; Sent 1 pkts, answer found in time: 329 msec 
	;; FROM: inet to SERVER: default -- 0.0.0.0
	;; WHEN: Wed Aug 11 12:45:52 1993
	;; MSG SIZE  sent: 43  rcvd: 71

But by advertising the name ``ftp.eff.org'', instead of ``kragar.eff.org'',
the administrator gains the flexibility to move the archive to some
other machine if necessary/desirable.  That's exactly the right way
to run such a service.