I have evaluated separating TCP+UDP checksums from pseudo-header, which gives some new applications: 1. ILNP - Identifier-Link Network Protocol. 2. IPsec-ESP-over-NAT-PT (one obstacle removed; not all) But slows down other traffic by 0.4% (assuming 1000-byte packets) - due to +4 bytes checksum at IP layer. So separating checksums into TCP+IP layers has trade-offs, not a simple improvement. -- -Alexey Eromenko "Technologov"