BGP Update Total Path Attribute Length field
The Total Path Attribute Length is a field found within the BGP Update message. According to the RFC, it is a 2-byte integer that indicates the total length of the Path Attributes field in octets. Its value allows the length of the Network Layer Reachability field to be determined.
A value of 0 indicates that neither the Network Layer Reachability Information (NRLI) field nor the Path Attribute field is present in this UPDATE message.
There can be multiple prefixes in one BGP update, but there is a limite to the total BGP message size. For more informationa about that, take a look at BGP Maximum message size.