IGRP Packet Format

Figure 4-3 shows the IGRP packet format. In this figure, you can see that IGRP updates provide more information than RIP and, at the same time, are more efficient. None of the fields in an IGRP packet is left unused; after the 12-octet header, each routing entry is filled one after another. Therefore, IGRP does not pad the update packet to force a 32-bit word boundary. With this efficient design, IGRP can carry a maximum of 104 fourteen-octet entries. Therefore, with its MTU size of 1500 bytes, IGRP can carry more routes per packet than RIP can.

Figure 4-3. IGRP Packet Format