Interesting Ethernet/UNIX 4.2 observation.


David C. Plummer (DCP@SCRC-QUABBIN.ARPA)
Fri, 21 Feb 86 10:18 EST


    Date: Thu, 20 Feb 86 23:35:17 EST
    From: jis@BITSY.MIT.EDU (Jeffrey I. Schiller)

    Moral of the story:

    1) The Ethernet topology described above may not be the best possible
       for an office area (but we all probably know that anyway).

    2) A Network Spy program like netwatch is an invaluable tool.

    3) WORKSTATIONS THAT ARE HAPPY TO ACT AS GATEWAYS are probably a BAD
       idea. In fact it is probably best that when a workstation receives
       a packet incorrectly sent to it, the packet be DISCARDed and
       perhaps logged for debugging purposes.
       Note that if a workstation sends an ICMP destination
       unreachable message back to the source, the monster
       collision would still occur as ALL workstations would try
       to send the ICMP message.

    4) Ethernet controllers that work "most" of the time may not be
       good enough.

There are two more morals:

    5) Unix is being antisocial by BROADCASTING information (rwhod) once
       a minute. As far as I know, only Unix cares about this.

    6) Unix is being antisocial by BROADCASTING requests (rwho) once
       every few minutes.

Consider 200 nodes on the same cable. That is a moral#5 broadcast
packet averaging 4 times a second, and a moral#6 packet at a hopefully
slower rate.

There are other things than Unix in the world. If Unix doesn't have
system configuration parameters to turn either or both of these off; it
should. Why must EACH Unix do this sort of thing all night long when
there is no user that is actually requesting the information. It's sort
of like me programming my machine to send a message to this mailing list
every half hour just to let everybody know my machine is still up.

Summary of morals 5 and 6: fix Unix.



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