[e2e] Question about fast path / slow path and IPv6

[Naidu, Venkata]

Michael,

-> This goes to the router people out there:
-> 
-> Is IP fast path / slow path processing (for packets carrying
-> IP options) similar for IPv4 and IPv6 in most current routers?

  I am trying to expand and explain your words "processing" and 
  "similar" clearly in technical terms:

  1. There is clearly a big difference between slow path vs fast 
     path. But the question is not that I hope. That question is 
     about IPv4 vs IPv6.

  2. Major changes between IPv4 and IPv6 are:

     * Fragmentation - IPv6 completely avoid fragmentation in
       transit routers. So the fragmentation "processing" 
       overhead is eliminated for IPv6.

     * Header Checksum - IPv6 assumes that lower layer checksums 
       are enough for hop-by-hop bit/packet integrity and
       higher-layer checksums are enough for end-end to 
       integrity. So checksum processing is eliminated in IPv6.
       (don

       Note that in IPv4 fragmentation and/or checksum in 
       transit routers is a rare event. 

     * Address/Tag lookup: Here comes some complex processing 
       as a function of input. Analyzing this is still a very
       big research area. If your routing tables are hierarchical,
       and placed in a well-designed optimized data structures 
       then the processing for IPv4 vs IPv6 is almost same (may  
       be in the order of O(clog*n) - * can be some Ackermann 
       function or a constant. The length of destination address 
       determines the constants c and n).

       AFAIK, IPv6 addresses are very hierarchical (as expected  
       to be maintained). So the routing table sizes are not as  
       much as in IPv4.

     * Options are well arranged in IPv6. Transit routers options
       are placed separately from end-routers options. 

  Finally (my conclusion) is IPv6 packet processing is little bit 
  fast when compared to IPv4 (in most of the cases).

Venkata.