3com S7906E Manuel De Montage

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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 
 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
 
 
Intradomain Routing Protocol Discriminator: Set to 0x83. 
Length Indicator: Length of the PDU header in bytes, including both common and specific headers. 
Version/Protocol ID Extension: Set to 1(0x01). 
ID Length: Length of the NSAP address and NET ID. 
R(Reserved): Set to 0. 
PDU Type: For details, refer to 
Version: Set to 1(0x01). 
Maximum Area Address: Maximum number of area addresses supported.