XPost: comp.os.vms   
   From: rick.jones2@hp.com   
      
   In comp.protocols.tcp-ip glen herrmannsfeldt  wrote:   
   > In comp.protocols.tcp-ip jbriggs444  wrote:   
   > < On Oct 2, 6:00?pm, glen herrmannsfeldt  wrote:   
   > <> Richard B. Gilbert  wrote:   
      
   > <> < I'm not certain but I suspect that your problem is due to the fact that   
   > <> < DECnet sets the Ethernet address to AA-00-04-00-FB-04. ?If you start   
   > <> < TCP/IP first, it will get the original hardware address for the   
   > <> < interface. ?When DECnet starts it will set the address to the DECnet   
   > <> < node address and leave TCP/IP swinging in the breeze!   
      
   > <> That should only happen until the ARP cache is updated. ?Any host   
   > <> that tries to connect after the MAC address change will get the   
   > <> new address from ARP. ?Most will update on the broadcast ARP reply,   
   > <> but maybe not all.   
   >   
   > < Broadcast ARP reply?  What broadcast ARP reply?   
      
   > OK, that is why I posted here.   
   >   
   > < ARP requests are broadcasts.   
   > < ARP replies are conventionally sent as unicasts.   
      
   > Other hosts should update their cache based on the broadcast   
   > request, though, right?   
      
   Should?  Perhaps.  Certainly they can.  Most probably do.   
      
   Some even went so far as to populate their ARP caches based on the   
   broadcast requests they saw - even before they tried to talk to that   
   system. I don't think there are any systems that do that foolish thing   
   any longer :)   
      
   > Many years ago I found a bug related to ARP.  An HP/UX machine   
      
   HP-UX :)   
      
   > running a third party appletalk (ethertalk) package would,   
   > it seems, sometimes ARP in SNAP encapsulated mode.  The Cisco   
   > router would then switch to SNAP encapsulation, but the host   
   > IP stack would not recognize them.  If I ping another host from   
   > the HP/UX machine it would ARP for that host, and the router   
   > would update the cache.   
      
   > I wouldn't be surprised if some broadcast replies.  How many   
   > update the cache on broadcast requests not destined for them?   
      
   Unless a gratuitous ARP happens to qualify as a reply (even though it   
   isn't) I don't think that ARP replies are ever sent as anything other   
   than unicast frames.   
      
   rick jones   
   --   
   firebug n, the idiot who tosses a lit cigarette out his car window   
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