User manual

xStack DES-3800 Series Layer 3 Stackable Fast Ethernet Managed Switch
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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with a neighboring router, a router may find that parts of its topological database are out of date.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:
Version No.
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
Checksum
Link-State Request Packet
3
Link-State Type
Link-State ID
Advertising Router
Figure 8- 19. Link-State Request Packet
Each advertisement requested is specified by its Link-State Type, Link-State ID, and Advertising
Router. This uniquely identifies the advertisement, but not its instance. Link-State Request packets are
understood to be requests for the most recent instance.