This read-write enumerated value configures the CRC (cyclic redundancy check) mode used for frame error detection on a particular HDLC-like interface, chosen among crc16(1), crc32(2), or crcnone(3), and defaults to crc16. An admin sets this to match whatever CRC mode the far-end device expects, since a mismatch would cause frames to be rejected as corrupted even when the link itself is healthy; crcnone disables the check entirely, which is rarely appropriate outside of testing. For example, an admin connecting to a peer that requires stronger error checking on a noisy long-haul circuit might change this from the default crc16(1) to crc32(2).