F3726, F3211, F3174, R5135, R3816-HP Firewalls and UTM Devices Appendix Protocol Reference-6PW100

24
Table 4 PDU types
T
yp
e PDU T
yp
e Acron
y
m
15 Level-1 LAN IS-IS hello PDU L1 LAN IIH
16 Level-2 LAN IS-IS hello PDU L2 LAN IIH
17 Point-to-Point IS-IS hello PDU P2P IIH
18 Level-1 Link State PDU L1 LSP
20 Level-2 Link State PDU L2 LSP
24 Level-1 Complete Sequence Numbers PDU L1 CSNP
25 Level-2 Complete Sequence Numbers PDU L2 CSNP
26 Level-1 Partial Sequence Numbers PDU L1 PSNP
27 Level-2 Partial Sequence Numbers PDU L2 PSNP
Hello PDU
IS-to-IS hello PDUs (IIHs) are used by routers to establish and maintain neighbor relationships. On
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 16 illu
strates the hello packet format in broadcast networks, where the blue fields are the common
header.
Figure 16 L1/L2 LAN IIH format
Major fields of the L1/L2 LAN IIH are as follows:
• Reserved/Circuit type—The first six bits are reserved with a value of 0. The last two bits indicate the
router type—00 means reserved, 01 indicates L1, 10 indicates L2, and 11 indicates L1/2.