This read-only two-octet octet string reports which CDP protocol versions the device supports, encoded as a bit string; for example, supporting versions 3 and 4 would appear as the big-endian bit pattern 00001100. An administrator checks this to confirm CDP version compatibility when troubleshooting why neighbor discovery isn't working between devices from different vendors or firmware generations. For example, if two devices fail to discover each other via CDP, the admin compares this version bitmask on each to check for a lack of overlapping supported versions.