3Com S7906E Configuration Manual page 719

Table 1-1 PDU type
Type
15 Level-1 LAN IS-IS hello PDU
16 Level-2 LAN IS-IS hello PDU
17 Point-to-Point IS-IS hello PDU
18 Level-1 Link State PDU
20 Level-2 Link State PDU
24 Level-1 Complete Sequence Numbers PDU
25 Level-2 Complete Sequence Numbers PDU
26 Level-1 Partial Sequence Numbers PDU
27 Level-2 Partial Sequence Numbers PDU
Hello
Hello packets are used by routers to establish and maintain neighbor relationships. A hello packet is
also called an IS-to-IS hello PDU (IIH). For broadcast networks, the Level-1 routers use the Level-1
LAN IIHs; and the Level-2 routers use the Level-2 LAN IIHs. The P2P IIHs are used on point-to-point
networks.
Figure 1-7 illustrates the hello packet format in broadcast networks, where the blue fields are the
common header.
Figure 1-7 L1/L2 LAN IIH format
Reserved/Circuit Type: The first 6 bits are reserved with a value of 0. The last 2 bits indicate the
router type. 00 means reserved, 01 indicates L1, 10 indicates L2, and 11 indicates L1/2.
Source ID: System ID of the router advertising the hello packet.
PDU Type
1-8
Acronym
L1 LAN IIH
L2 LAN IIH
P2P IIH
L1 LSP
L2 LSP
L1 CSNP
L2 CSNP
L1 PSNP
L2 PSNP