XPost: comp.os.linux.networking   
   From: bruce-usenet@noreplybicycle.synonet.comnoreply   
      
   Rob Warnock wrote:   
      
   > glen herrmannsfeldt   wrote:   
   > +---------------   
   > | Rob Warnock  wrote:   
   > | > Beware that in some (most?) versions of Linux "ifconfig" will set the   
   > | > IP broadcast address *incorrectly* unless you specify it explicitly   
   > | > [thus causing various protocols that use IP broadcast for initial   
   > | > discovery to fail mysteriously!].   
   > |   
   > | I don't know what you mean by incorrect...   
   > +---------------   
   >   
   > I forget the exact scenario, but ISTR[1] if you did something like this:   
   >   
   >     ifconfig eth0 10.2.3.4 netmask 255.255.255.192   
   >   
   > then the broadcast address came up with 10.255.255.255, which is   
   > *definitely* the wrong value!! That is, it looked only at the   
   > Class A nature of 10.2.3.4 and ignored the netmask.   
      
   This was done this way because it used to be standard to always use the .255   
   address as the bcast address regardless of VLSM.  This effectively gave you   
   an extra address in your address space & when you saw a .255 you knew what   
   it was.   
      
   The downside was that it would screw up people trying to broadcast into   
   other subnets if they happened to be in the same classfull address space.   
      
   Bruce   
      
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