Zero-based offset of an arbitrary field within the packet. Depending upon the value of filterFlags, the offset is relative to the start of the translated packet, beginning with the big endian MAC addresses; or, the offset is relative to the start of the data past the IP header (and, the packet must be an IP packet with a valid IP header); or, the offset is relative to the start of the data past the Source Routing information (presence of Source Routing information is optional).