Replication traffic integrity checking is not enabled for resources by default. To enable it, add the following lines to your resource configuration in /etc/drbd.conf:

resource resource
  net {
    data-integrity-alg algorithm;
  }
  ...
}

algorithm may be any message digest algorithm supported by the kernel crypto API in your system's kernel configuration. Normally, you should be able to choose at least from sha1, md5, and crc32c.

If you make this change to an existing resource, as always, synchronize your drbd.conf to the peer, and run drbdadm adjust resource on both nodes.