For an originating NAT to pass TCP or UDP successfully, it must recompute the TCP / UDP header checksum based on the translated IP addresses, not the original ones, and put that checksum into the TCP / UDP header of the first packet of the fragmented set of packets.
32.
Jim Gettys, responsible for the laptops'system software, has called for a re-education of programmers, saying that many applications use too much memory or even leak memory . " There seems to be a common fallacy among programmers that using memory is good : on current hardware it is often much faster to recompute values than to have to reference memory to get a precomputed value.
33.
Integrity protection is assumed to be assured by both the link layer or error detection and correction methods in higher-layer protocols, such as TCP and UDP . In IPv4, UDP may actually have a checksum of 0, indicating no checksum; IPv6 requires a checksum in UDP . Therefore, IPv6 routers do not need to recompute a checksum when header fields change, such as the time to live ( TTL ) or hop count.
