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Link-State Acknowledgment Packet
Link-State Acknowledgment packets are OSPF packet type 5. To make the folding of link-state adver-
tisements reliable, flooded advertisements are explicitly acknowledged. This acknowledgment is ac-
complished 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 acknowl-
edged, 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
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 ’s
current instance.