On 5/3/2015 7:53 PM, Xuxiaohu wrote: >>> As >>> > > such, it's not recommended to perform fragmentation on the tunnel >>> > > layer and the outer IP layer. >> > >> > It's provably required for IPv4 DF=1 and IPv6. > > If the IPv4 packets with DF=1 and IPv6 packets are transported over > Ethernet, do you still want the Ethernet layer to do fragmentation?
The proof is for IP in anything that eventually goes over IP again. If you put IP in Ethernet and then put that pack in IP (e.g., via PPP, EtherIP, or GRE), then the tunnel will need to support fragmentation. The question is "what layer provides the tunnel". If you treat the entire set of headers of encapsulation as a set, you can use any layer in that set you want. If you treat UDP as the sole controllable encapsulation layer, then you need to support fragmentation there. The ONLY reason IP doesn't require fragmentation over Ethernet is because the IP layer directly above Ethernet has an MTU of 1280 (for IPv6) or 68 (for IPv4) and Ethernet supports an MTU of 1500. Joe _______________________________________________ Int-area mailing list [email protected] https://www.ietf.org/mailman/listinfo/int-area
