D-Link DXS-3326GSR Manual page 157

Version No.
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.
The format of this packet is similar to that of the Data Description packet. The body of both packets is simply a list of link-
state advertisement headers.
The format of the Link-State Acknowledgment packet is shown below:
Version No.
Each acknowledged link-state advertisement is described by its link-state advertisement header. It contains all the
information required to uniquely identify both the advertisement and the advertisement's current instance.
DXS-3326GSR Gigabit Layer 3 Switch
Link-State Update Packet
4
Checksum
Number of Advertisements
Link-State Advertisements ...
Figure 7- 22. Link-State Update Packet
Link-State Acknowledgment Packet
5
Checksum
Link-State Advertisement Header ...
Figure 7- 23. Link State Acknowledge Packet
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
144