80 	case IPPROTO_TCP:  // For TCP & UDP the checksum neutrality of the chosen IPv6  in sched_cls_ingress6_nat_6_prog()
83 	case IPPROTO_ESP:  // since there is never a checksum to update.  in sched_cls_ingress6_nat_6_prog()
108 	// Calculate the IPv4 one's complement checksum of the IPv4 header.  in sched_cls_ingress6_nat_6_prog()
119 	// Calculate the *negative* IPv6 16-bit one's complement checksum of the IPv6 header.  in sched_cls_ingress6_nat_6_prog()
125 	// Note that there is no L4 checksum update: we are relying on the checksum neutrality  in sched_cls_ingress6_nat_6_prog()
182 	// Calculate the IPv4 one's complement checksum of the IPv4 header.  in sched_cls_egress4_snat4_prog()
191 	// for a correct checksum we should get *a* zero, but sum4 must be positive, ie 0xFFFF  in sched_cls_egress4_snat4_prog()
204 	case IPPROTO_TCP:  // For TCP & UDP the checksum neutrality of the chosen IPv6  in sched_cls_egress4_snat4_prog()
207 		break;         // since there is never a checksum to update.  in sched_cls_egress4_snat4_prog()
213 		// If IPv4/UDP checksum is 0 then fallback to clatd so it can calculate the  in sched_cls_egress4_snat4_prog()
214 		// checksum.  Otherwise the network or more likely the NAT64 gateway might  in sched_cls_egress4_snat4_prog()
215 		// drop the packet because in most cases IPv6/UDP packets with a zero checksum  in sched_cls_egress4_snat4_prog()
216 		// are invalid. See RFC 6935.  TODO: calculate checksum via bpf_csum_diff()  in sched_cls_egress4_snat4_prog()
246 	// Calculate the IPv6 16-bit one's complement checksum of the IPv6 header.  in sched_cls_egress4_snat4_prog()
260 	// However, we've already verified the ipv4 checksum is correct and thus 0.  in sched_cls_egress4_snat4_prog()