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xStack DES-3800 Series Layer 3 Stackable Fast Ethernet Managed Switch
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Database Description Packet
Database Description packets are OSPF packet type 2. These packets are exchanged when an adjacency is being initialized. They
describe the contents of the topological database. Multiple packets may be used to describe the database. For this purpose, a poll-
response procedure is used. One of the routers is designated to be master, the other a slave. The master sends Database
Description packets (polls) that are acknowledged by Database Description packets sent by the slave (responses). The responses
are linked to the polls via the packets’ DD sequence numbers.
Database Description Packet
Version No.
2Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
Checksum
Options
DD Sequence No.
Reserved
Reserved
Link-State Advertisement Header ...
IM
MS
Figure 8- 21. Database Description Packet
Field Description
Options The optional capabilities supported by the router.
I - bit The Initial bit. When set to 1, this packet is the first in the sequence
of Database Description packets.
M - bit The More bit. When set to 1, this indicates that more Database
Description packets will follow.
MS - bit The Master Slave bit. When set to 1, this indicates that the router is
the master during the Database Exchange process. A zero
indicates the opposite.
DD Sequence Number User to sequence the collection of Database Description Packets.
The initial value (indicated by the Initial bit being set) should be
unique. The DD sequence number then increments until the
complete database description has been sent.
The rest of the packet consists of a list of the topological database’s pieces. Each link state advertisement in the database is
described by its link state advertisement header.