Upstream reassembly with small first IPv6 fragments less than 1280 bytes

This functionality is disabled by default, and can be explicitly enabled by configuring the min-first-fragment-size-rx command under the DS-lite configuration.

Classic CLI:

config
   router / service vprn 
      nat
         inside
               dual-stack-lite
                         address  <AFTR IPv6 address> 
                              min-first-fragment-size-rx <512..1280>

MD-CLI:

configure {
   router {
      nat {
         inside {
            large-scale {
               dual-stack-lite {
                  endpoint <AFTR IPv6 address> {
                     min-first-fragment-size-rx <512..1280>
                  }
               }
            }
         }
      }
   }
}