In summary, MSTP encodes some additional information in its BPDU regarding region information and configuration, each of these messages conveys the spanning tree information for each instance. Each instance can be assigned several configured VLANs, frames (packets) assigned to these VLANs operate in this spanning tree instance whenever they are inside the MST region. To avoid conveying their entire VLAN to spanning tree mapping in each BPDU, bridges encode an MD5 digest of their VLAN to instance table in the MSTP BPDU. This digest is then used by other MSTP bridges, along with other administratively configured values, to determine if the neighboring bridge is in the same MST region as itself.