xStack® DGS-3120 Series Layer 3 Managed Gigabit Ethernet Switch Web UI Reference Guide
186
Database Description Packet
Version No.
2
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
Checksum
Options
DD Sequence No.
Reserved
Reserved
Link-State Advertisement Header ...
I MMS
Figure 5-33 Database Description Packet
Parameter
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.
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neighboring router, a router may find that parts of its topological database are out of date.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:
Summary of Contents for xStack DGS-3120 Series
Page 1: ......