D-Link DES-3350SR User Manual - page 118
D-Link DES-3350SR Standalone Layer 3 Switch
108
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 9 - 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.
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:
Version No.
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
Checksum
Link-State Update Packet
4
Number of Advertisements
Link-State Advertisements ...
Figure 9 - 20. Link-State Update Packet
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.
Depending on the state of the sending interface and the source of the advertisements being acknowledged, a Link-State
Acknowledgment packet is sent either to the multicast address AllSPFRouters, to the multicast address AllDRouters, or as a
unicast packet.