D-Link DGS-3600 Series User Manual page 191

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.
Link-State Update Packet
Link-State Update packets are OSPF packet type 4. These packets implement the flooding of link-state advertisements. Each
Link-State Update packet carries a collection of link-state advertisements one hop further from its origin. Several link-state
advertisements may be included in a single packet.
Link-State Update packets are multicast on those physical networks that support multicast/broadcast. In order to make the
flooding procedure reliable, flooded advertisements are acknowledged in Link-State Acknowledgment packets. If retransmission
of certain advertisements is necessary, the retransmitted advertisements are always carried by unicast Link-State Update packets.
The format of the Link-State Update packet is shown below:
The body of the Link-State Update packet consists of a list of link-state advertisements. Each advertisement begins with a
common 20-byte header, the link-state advertisement header. Otherwise, the format of each of the five types of link-state
advertisements is different.
Link-State Acknowledgment Packet
Link-State Acknowledgment packets are OSPF packet type 5. To make the folding of link-state advertisements reliable, flooded
advertisements are explicitly acknowledged. This acknowledgment is accomplished through the sending and receiving of Link-
State Acknowledgment packets. Multiple link-state advertisements can be acknowledged in a single Link-State Acknowledgment
packet.
xStack DGS-3600 Series Layer 3 Gigabit Ethernet Managed Switch
Link-State Request Packet
3
Version No.
Checksum
Figure 8- 31. Link-State Request Packet
Link-State Update Packet
4
Version No.
Checksum
Number of Advertisements
Link-State Advertisements ...
Figure 8- 32. Link-State Update Packet
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
Link-State Type
Link-State ID
Advertising Router
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
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