    Network Working Group                            Ralph Alter
    RFC #305                                         BBN
    NIC #9078                                        23 February 1972

                              UNKNOWN HOST NUMBERS
                              --------------------

       In response to a recent minor flurry of confusion, it seems worth
       announcing publicly the fact that new IMPs are tested (almost
       always) on the ARPA Net here at BBN before delivery to the intended
       site.  Accordingly, sites should not be surprised to receive RFCs
       or at least RSTs from IMPs or Hosts they thought didn't exist, or
       at least did not exist yet.

       Occasionally, IMPs of some given configuration are tested in a
       mode where they announce their IMP number as different from what
       it will be when finally installed.  A variety of reasons may create
       such a situation.  The latest such occurrence is that a TIP, to be
       installed shortly at ETAC with IMP number 20 (replacing the 316
       IMP now at ETAC which is number 20) was recently tested here with
       McClellan's IMP number (22).  (It couldn't be tested with its own
       number since the 316 IMP currently at ETAC is using that number.)
       The result was RSTs from the TIP (Host 3) at IMP 22 - which is
       network address 150 (226 octal or 96 hex).

       One site asked if their Host tables needed updating.  The answer
       is _NO_.  We fully expect IMPs tested under these circumstances to be
       ignored or CLS'd by some Hosts.  We suggest that Host tables (where
       they are thought to be necessary) be modified only in response to
       official notification from BBN via either an RFC or an update to
       Appendix A of BBN Report #1822.

       RA/jm

           [ This RFC was put into machine readable form for entry ]
           [ into the online RFC archives by BBN Corp. under the   ]
           [ direction of Alex McKenzie.                   12/96   ]

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