IS-IS Overview 333
Figure 105 L1/L2 LAN IIH format
■ 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 106 shows the hello packet format on the point-to-point network.
Intradomain routing protocol discriminator
Reserved
Version
R
ID length
Version/Protocol ID extension
Length indicator
Maximum area address
R R PDU type
No. of Octets
1
1
1
1
1
1
1
1
Reserved/Circuit type
Source ID
Holding time
PDU length
R
LAN ID
Variable length fields
1
ID length
2
2
1
Priority
ID length+1
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