322e5b05   
   XPost: comp.arch.embedded   
   From: philip+usenet@paeps.cx   
      
   Didi  wrote:   
   > On Feb 2, 9:38 pm, Nobody  wrote:   
   >> If your routing table specifies that a given IP address should be routed   
   >> via the default gateway, then any ARP entries for that IP address won't   
   >> make the slightest bit of difference, as the computer will never request   
   >> an ARP entry for the IP address, it will request one for the gateway.   
   >   
   > Indeed. But if you **manually** set an ARP entry for an IP address in the   
   > table (like I explained in my first post, one day I will get tired of   
   > initiating threads...) because you know this IP address is on the same wire   
   > routing towards the gateway rather than the specified MAC address will at   
   > best double the network traffic for that address.   
      
   Adding a static ARP entry does not tell the IP stack anything though.   
      
   The IP stack will try to find a route to the destination address in the IP   
   header in the routing table.  If it doesn't find a specific route, the packet   
   will be sent to the default router.   
      
   Only if you have a route to the network, will your entry be found.  The ARP   
   lookup happens _after_ an IP routing decision has been taken, not before.  If   
   you have no route to the network (such as a network route by virtue of having   
   an address in the same network on an interface) the routing decision will be   
   to use the default router.   
      
   You can add a hundred arbitrary static arp entries.  If you have no routes   
   pointing to them, they won't ever be consulted.   
      
    - Philip   
      
   --   
   Philip Paeps                                    Please don't email any replies   
   philip@paeps.cx                                     I follow the newsgroup.   
      
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