D-Link DGS-3612G Product Manual - Page 222

xStack® DGS-3600 Series Layer 3 Managed Gigabit Ethernet Switch Database Description Packet Version No. 2 Packet Length Checksum Router ID Area ID Authentication Type Authentication Authentication Reserved I M MS Reserved Options DD Sequence No. Link-State Advertisement Header ... Figure 4- 41. Database Description Packet Field 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Database Description packets with a neighboring router, a router may find that parts of its topological database are out of date.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 LinkState 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: 206