In IPv4 and IPv6, pseudo-header mandates checksum at Layer 4, and also cover IP. In IP-FF, I plan to remove "pseudo-header" from Layer 4 checksum, for a few reasons: 1. IPsec ESP Transport mode over NAT-PT (NAPT). (one obstacle gets removed, and I will deal with the rest later -- IPsec-NAT looks like a can-of-worms for now) 2. ILNP protocol will become possible. (as an extension protocol) 3. better layer separation ...and I don't have checksum at Layer 3 either. (like in IPv6) Do we actually need chcksums at Layer 3 ? Disadvantages: * Slow-down of Core Routers. Do we even need IP-layer checksums ? * Most Data-link layer protocols cover "data"; That is Layers 3-to-7 in CRC; one notable exception is ATM. Can I assume that layer 2 CRC protects me ? * a single mis-routed packet shouldn't cause too much trouble. * in IPv6, the options / extensions are not protected by checksum either. (not at layer 3, not at layer 4 -- maybe only at layer 2) Any advantages ? * prevents single mis-routed packets, or a bad option from getting through. Quick analysis of Data-link layer's checksum protection: ATM: Header-only, 8-bit. Frame Relay: 16 bit. Ethernet and WiFi - 32-bit FCS. (WiFi also has re-transmission) Token Ring - 32-bit FCS Point-to-Point Protocol (PPP) with 16 or 32 bits CRC. 4G/LTE: 24-bit CRC, +2nd level CRC. Firewire IEEE-1394: 32-bit CRC. Quick result: besides ATM, everybody else seems to cover both headers and all data. -- -Alexey Eromenko "Technologov"