H3C LS-3100-52P-OVS-H3 Operation Manual page 618

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.
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.
Priority: DIS priority.
LAN ID: Includes the system ID and a one-byte pseudonode ID.
Figure 1-8 shows the hello packet format on the point-to-point networks.
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