H3C Technologies H3C S12500 Series Switches - Manual (Page 154)

138
Type PDU Type Acronym
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
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 58 illustrates the hello packet format in broadcast networks, where the blue fields are the common
header.
Figure 58 L1/L2 LAN IIH format
Major fields of the L1/L2 LAN IIH are as follows:
• 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.
• Holding time—If no hello packets are received from the neighbor within the holding time, the
neighbor is considered down.
• PDU length—Total length of the PDU in bytes.