D-Link DGS-3324SR User Manual page 119

D-Link DGS-3324SR Layer 3 Stackable Gigabit Ethernet Switch
other a slave. The master seconds Database Description packets (polls) which 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
Field
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.
The 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neighboring router, a router may find that parts of its topological database are out of date.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.
A router that sends a Link-State Request packet has in mind the precise instance of the database pieces it is
requesting, defined by LS sequence number, LS checksum, and LS age, although these fields are not specified in
the Link-State Request packet itself. The router may receive even more recent instances in response.
The format of the Link-State Request packet is shown below:
Database Description Packet
2
Router ID
Area ID
Checksum
Authentication
Authentication
I M MS
Reserved
DD Sequence No.
Link-State Advertisement Header ...
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.
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.
Table 4- 10. Database Description Packet
Packet Length
Authentication Type
Options
104