D-Link DES-3326 User Manual page 78

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.
The 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:
Link-State Update Packet
4
Version No.
Checksum
Number of Advertisements
Link-State Advertisements ...
Figure 5-30. Link-State Update Packet
Link-State Acknowledgment Packet
Version No. 5
Checksum
Link-State Advertisement Header ...
Figure 5-31. Link-State Acknowledgement Packet
DES-3326 Layer 3 Fast Ethernet Switch User's Guide
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
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