3Com S7906E - Switch, Configuration Manual

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1-7
On IS-IS broadcast networks, all routers are adjacent with each other. However, the DIS is responsible
for the synchronization of their LSDBs.
IS-IS PDU Format
PDU header format
IS-IS packets are encapsulated into link layer frames. The Protocol Data Unit (PDU) consists of two
parts, the headers and the variable length fields, where the headers comprise the PDU common header
and the PDU specific header. All PDUs have the same PDU common header, while the specific headers
vary by PDU type. The following figure shows the PDU format.
Figure 1-5 PDU format
Common header format
Figure 1-6 shows the PDU common header format.
Figure 1-6 PDU common header format
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
z
Intradomain Routing Protocol Discriminator: Set to 0x83.
z
Length Indicator: Length of the PDU header in bytes, including both common and specific headers.
z
Version/Protocol ID Extension: Set to 1(0x01).
z
ID Length: Length of the NSAP address and NET ID.
z
R(Reserved): Set to 0.
z
PDU Type: For details, refer to Table 1-1 .
z
Version: Set to 1(0x01).
z
Maximum Area Address: Maximum number of area addresses supported.