Figure 5-34 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:
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