D-Link DES-3326SR User Manual page 139

DES-3326SR Layer 3 Fast Ethernet Switch User's Guide
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 Acknowledgment Packet
Packet Length
Version No. 5
Router ID
Area ID
Checksum
Authentication Type
Authentication
Authentication
Link-State Advertisemen t Header ...
Figure 5-27. Link-State Acknowledgement Packet
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