This is a bit mask with 1 bits indicating positions in the effective destination address from which embedded SNPA information is to be extracted, with the mask's first octet aligned to the NSAP address's first octet and the shorter of the two padded with zeros if lengths differ. This is the extraction template used when ciiRAMapType is extractIDI or extractDSP, telling the router precisely which bits of the destination NSAP address encode the SNPA information needed to forward the packet, meaningful only on OSI networks where SNPA is systematically embedded in the destination address structure. For example, getting this bitmask misaligned by even a few bits would cause the router to extract the wrong SNPA address from an otherwise correctly addressed destination, silently misdirecting traffic rather than producing an obvious error.