ecbc4efc   
   From: rick.jones2@hp.com   
      
   Albert Manfredi  wrote:   
   > On Nov 20, 2:57?pm, karthikbalaguru    
   > wrote:   
   > > Hi,   
   > > Unlike IPv4, when UDP packets are originated by   
   > > an IPv6 node, the UDP checksum is not optional.   
   > > But, why is it mandatory in IPv6 ? Any ideas ?   
      
   > This was the topic of some lengthy debate in the 6man wg of the IETF.   
      
   > The original reason was that unlike IPv4, IPv6 does not include a   
   > packet checksum in the IP header. So that if the UDP checksum were   
   > not made mandatory, there would be nothing protecting that UDP/IP   
   > packet at all.   
      
   That might be more accurately put as IPv6 does not include an IP   
   *header* checksum - someone reading "packet checksum" might mistakenly   
   conclude the IPv4 header checksum includes the data of the IP   
   datagram.  The checksum in IPv4 only covers the IPv4 header, to verify   
   that there were no bit errors in the header.   
      
   With a mandatory UDP checksum (I'm sure the streaming types like   
   that...) when going over IPv6 you can still get misdirected IPv6   
   datagrams, but ostensibly some of them will be tossed at the   
   destination when they get to UDP and the UDP checksum fails thanks to   
   the inclusion of the "pseudo header" (IIRC).   
      
   IMO it is a perfect example of the sway the "router guys" had in   
   defining IPv6 - now they have no IP header checksum to check or   
   otherwise worry about.   
      
   rick jones   
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