The Database Description Packet - D-Link dxs-3350sr Installation & User Manual

The 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
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.
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router, a router may find that parts of its topological database are out of date.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.
DXS-3350SR Gigabit Layer 3 Switch
Database Description Packet
2
Version No.
Checksum
Reserved
I M MS
Reserved
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.
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
Options
DD Sequence No.
150