D-Link xStack Reference Manual page 214

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xStack DGS-3620 Series Layer 3 Managed Stackable Gigabit Switch Web UI Reference Guide
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 seconds 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.
Version No.
Reserved
Parameter
Options
I-bit
M-bit
MS-bit
DD Sequence Number
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.
Link-State Request Packet
Link-State Request packets are OSPF packet type 3. After exchanging Database Description packets with a
neighboring router, a router may find that parts of its topological database are out of date. The Link-State Request
packet is used to request the pieces of the neighbor's database that are more up to date. Multiple Link-State
Request packets may need to be used. The sending of Link-State Request packets is the last step in bringing up
an adjacency.
Database Description Packet
2
Router ID
Checksum
I M MS
Reserved
DD Sequence No.
Link-State Advertisement Header ...
Figure 6-31 Database Description Packet
Description
The optional capabilities supported by the router.
The Initial bit. When set to 1, this packet is the first in the sequence of Database
Description packets.
The More bit. When set to 1, this indicates that more Database Description packets
will follow.
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.
Used 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.
Packet Length
Area ID
Authentication Type
Authentication
Authentication
Options
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