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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
Switch Management and Operating Concepts 149
Figure 5-25. 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.
The 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: