Figure 19-2 shows the I PX packet format. There is no packet fragmentation. When the value of this field reaches 15, the packet is discarded under the assumption that a routing loop might be occurring. Although IPX was derived from XNS, it has several unique features. From the standpoint of routing, the encapsulation mechanisms of these two protocols are the most important difference.
Encapsulation is the process of packaging upper-layer protocol information and data into a frame.
For Ethernet, XNS uses standard Ethernet encapsulation, whereas IPX packets are encapsulated in Ethernet Version 2.0 or IEEE 802.3 without the IEEE 802.2 information that typically accompanies these frames. Figure 19-3 illustrates Ethernet, standard IEEE 802.3, and IPX encapsulation. Note NetWare 4.0 supports encapsulation of IPX packets in standard IEEE 802.3 frames. Like XNS, RIP derived from work done at Xerox for the XNS protocol family. Using NetWare's LU 6.2 capability, NetWare nodes can exchange information across an IBM network.