This counts instances where the version field within the SIP3 header extension was invalid or unrecognized, distinct from the length check in lportSmdsCntSip3HeLenInvalids and specific to whether this switch recognizes the extension's stated version. An admin treats a rising count here as a possible sign of a version mismatch between this switch's SMDS software and whatever equipment is generating that header extension, perhaps after a carrier-side upgrade introduced a newer extension version this switch does not understand. For example, a jump in lportSmdsCntSip3HeVersionInvalids after a carrier network upgrade elsewhere would be a strong hint that the new equipment is stamping header extensions with a version this switch's firmware does not recognize.