UTP FOOBAR (SOLUTION)

[John Kemp]

This is a summary of a network problem, the probable cause,
and the probable solution.  At this point, there are
indications that the problem has been corrected.

Problems:
     1) campus gateway sending out "giant packets"
     2) IBM 320 network software choking and dying on 1)
     3) DEC vs2000-uVAXII vaxcluster dropping connections
     4) PLEXCOMM utp repeater showing high number of collisions

A campus networking analyst hooked a lanalyzer up to our net to examine
the problem.  It appears that the gateway was sending out RIP packets 
in extremely large ethernet frames (16Kbytes).  And there were also a 
lot of "broken" packets being sent out. This was evidenced by a high 
number of CRC errors and short packets.

Solutions:
     1) uVAXII moved off thick cable, to repeater using AUI-UTP 
     2) DEC transceivers and thick backbone cable junked
    *3) ODS 234 FOT replaced with Cabletron FOT
     4) gateway updated to current software and hardware revs

Our analyst thinks the ODS FOT (fiber optic transceiver) was the 
most likely cause of the weirdness.  The ODS operated as a "host" 
connected to our thick cable.  The Cabletron operates somewhat 
differently and connects straight into the AUI port on the repeater.

Personally, I tend to think that the DEC transceivers didn't help 
things any either.  We have had trouble connecting things to them 
in the past.  

And of course, the IBM software choking and dying is an obvious software 
deficiency.  I would hope that IBM fixes this in their next release of
AIX.  Just send a 16KB packet to your RS6000 and see what happens.

Below are diagrams of before and after configuration.  I hope this 
information is helpful to someone else.  The analysts conclusion
so far is that UTP is not the problem.

Questions and comments welcome...
--------  john kemp            (  (  )_  internet - kemp at uiatma.atmos.uiuc.edu
  -----                       (  (   __)   decnet - uiatmb::kemp
   ---    univ of illinois   (_ (   __)    bitnet - {uunet,convex}
   --     dept of atmos sci  .(____).               !uiucuxc!uiatma!kemp
   -      105 s gregory ave    ...          phone - (217) 333-6881
    -     urbana, il 61801    ...             fax - (217) 444-4393

Glossary:

... fiber      --- thin      === thick      ~~~ UTP

Tx -- DEC AUI transceiver      Ax -- TP-AUI transceiver
Bx -- TP-BNC transceiver       UTPR -- Plexcomm multiport UTP repeater
ODS -- Fiber Transceiver       FIOL -- Cabletron Fiber Link
xxx -- more computers

------------------------- BEFORE -------------------------------------

Gway ... ODS =====                  ===== uvaxII
                 Tx ====== Tx ===== Tx 
                           =                                                
                           UTPR ~~~ Ax === ibm320                              
                                ~~~ Bx --- sun --- vs2000                      
                                ~~~
                                ~~~
                                ~~~
                                ~~~
                                ~~~ Ax === xxx
                                ~~~ Bx --- xxx 
                                ~~~ Bx --- xxx --- xxx
                                ~~~ Bx --- xxx --- xxx --- xxx
   
------------------------- AFTER -----------------------------
   
Gway ... FIOL ====== UTPR ~~~ Ax === uvaxII
                          ~~~ Ax === ibm320                          
                          ~~~ Bx --- sun --- vs2000                      
                          ~~~
                          ~~~
                          ~~~
                          ~~~ Ax === xxx
                          ~~~ Bx --- xxx 
                          ~~~ Bx --- xxx --- xxx
                          ~~~ Bx --- xxx --- xxx --- xxx
 
------------------------- END -------------------------------------