> NA(P)T is fundamentally incompatible with the guarantees set out by the IP standards that specify packets to be transmitted unmodified end-to-end. A small ni

> NA(P)T is fundamentally incompatible with the guarantees set out by the IP standards that specify packets to be transmitted unmodified end-to-end. A small nitpick, but some fields of the IP packet are meant to be modified in transit. For instance, the TTL, the ECN marking bit, and the fragment fields. The checksum field is defined so it can be updated (without being recomputed) to match these changes. But yeah, other than these fields in the IP header, and a few hop-by-hop headers or options, packets are not meant to be modified in transit (other than fragmentation, but this applies once the packet fragments are put together).