IDP Packet Format
Transport control: An 8-bit field that contains hop count and maximum packet lifetime (MPL) subfields. The hop count subfield is initialized to zero by the source and incremented by one as the datagram passes through a router. When the hop count field reaches 16, the datagram is discarded on the assumption that a routing loop is occurring. The MPL subfield provides the maximum amount of time, in seconds, that a packet can remain on the internetwork.