This read-only Counter64 counts the total number of input bytes received through the VPDN tunnel, providing a wider counter than the 32-bit cvpdnTunnelBytesIn to avoid wraparound on high-throughput tunnels. Administrators use this as the preferred long-term measure of inbound tunnel traffic volume, especially on tunnels carrying substantial or sustained data volume. For example, when building a monitoring dashboard for a busy VPDN tunnel, an admin would graph this 64-bit counter rather than its 32-bit predecessor to get an accurate, non-wrapping traffic trend.