HP OpenVMS Systems

DECnet packet sizes?

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The Question is:

 
DECnet phase IV: buffer size as displayed by
NCP command show exec char.  Default is 576,
which I interpret to be 512 bytes + 64 bytes
overhead.  For systems that have only Ethernet,
is 576 the correct value? Seems to me that
1492? + 64 = 1556 would be a better value for
preventing packet splits.  If not 1556, what
would be the "best" value for Ethernet?
 
 

The Answer is :

 
  In general, the OpenVMS Wizard would recommend not messing with this.
  Failure to heed this recommendation can cause mysterious DECnet problems
  either now or -- as the DECnet configuration changes -- in the future.
 
  Ethernet supports packets up to 1498.
 
  FDDI supports up to 4468.
 
  Also check for sufficient EXECUTOR BUFFER SIZE and EXECUTOR SEGMENT
  BUFFER SIZE parameter settings.  On OpenVMS releases with the SYSGEN
  parameter LRPSIZE, check the setting of LRPSIZE as well.
 
  If you have point-to-point links any in your DECnet network, you will want
  to remain with the default 576 byte packet size.  Packets larger than those
  supported by any intervening DECnet Phase IV routers are simply dropped.
 
  If you want to use larger packet sizes, an upgrade to DECnet-Plus is
  recommended -- DECnet-Plus handles packet fragmentation.
 

  

     

     
answer written or last revised on ( 15-FEB-1999 )
     
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