3Com MSR 50 Series Configuration Manual page 884

884 C 57: IS-IS C
HAPTER ONFIGURATION
Table 41 PDU type
Type PDU Type
27 Level-2 Partial Sequence Numbers PDU
Hello
The hello packet is used by routers to establish and maintain the neighbor
relationship. It is also called IS-to-IS hello PDU (IIH). For broadcast network, the
Level-1 router uses the Level-1 LAN IIH; and the Level-2 router uses the Level-2
LAN IIH. The P2P IIH is used on point-to-point network.
Figure 259 illustrates the hello packet format in broadcast networks, where the
blue fields are the common header.
Figure 259 L1/L2 LAN IIH format
Intradomain routing protocol discriminator
Length indicator
Version/Protocol ID extension
ID length
R R R
Version
Reserved
Maximum area address
Reserved/Circuit type
Source ID
Holding time
PDU length
R Priority
LAN ID
Variable length fields
Reserved/Circuit Type: The first 6 bits are reserved with value 0. The last 2 bits
■
indicates router types: 00 means reserved, 01 indicates L1, 10 indicates L2, and
11 indicates L1/2.
Source ID: The system ID of the router advertising the hello packet.
■
Holding Time: If no hello packets are received from a neighbor within the
■
holding time, the neighbor is considered dead.
PDU Length: The total length of the PDU in bytes.
■
Priority: DIS priority.
■
LAN ID: Includes the system ID and one byte pseudonode ID.
■
Figure 260 shows the hello packet format on the point-to-point network.
No. of Octets
1
1
1
1
PDU type 1
1
1
1
1
ID length
2
2
1
ID length+1
Acronym
L2 PSNP