RFC 1681 (rfc1681) - Page 2 of 5


On Many Addresses per Host



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RFC 1681               On Many Addresses per Host            August 1994


   Security is another reason, in some cases.  Address-based
   authentication is bad enough; relying on the name service adds
   another layer of risk.  An attacker can go after the DNS, in that
   case.  A risk-averse system manager might prefer to avoid the extra
   exposure, instead granting privileges (i.e., rlogin or NFS) by
   address instead of name.  But that, of course, leads to all the usual
   headaches when the location of the service changes.  If the address
   for the service could be held constant, there would be much more
   freedom to move it to another machine.  One way to do that is by
   assigning the serving host a secondary address.

   A related notion comes from the need to offer different views of a
   service from a single host.  For example, research.att.com has long
   offered two distinct FTP archives, with slightly different access
   policies.  It would be nice if both could live on the same machine,
   without asking the user community to learn new protocols or custom
   port numbers.

   Archie is an even better example.  There are three principal ways to
   use Archie:  use a special protocol, and hence a special application
   program, on a dedicated port and host that is probably named
   archie.foo.bar; telnet to archie.foo.bar and go through an extra and
   gratuitous login as archie, or telnet to some special port on
   archie.foo.bar.  The latter two are examples of using a standard
   protocol (telnet) to offer a different service.  Neither alternative
   is very convenient.

   It would be better if archie.foo.bar provided the Archie service,
   while host.foo.bar provided a login prompt.  Again -- an easy way to
   do this is to assign the host a separate IP address for its extra
   service.

   Note that there are security advantages here, too.  A firewall could
   be configured to allow access to the address associated with the
   Archie server, but not the other addresses on that host.  That would
   provide a high degree of safety, assuming, of course, that the other
   servers on that host were bound to its primary addresses, and not the
   exposed address.

   Another way to implement this concept would be to extend the DNS, to
   return port number information as well as IP addresses.  Thus,
   netlib.att.com might return 192.20.225.3/221.  But that would
   necessitate changing every FTP client program, a daunting task.

   We could also look on this as the extension of the MX concept.  MX
   records are very valuable, but they apply only to mail, and they
   don't supply port numbers.  Again, changing this would require
   massive client program changes.



Bellovin