D-Link DGS-3324SR User Manual page 120

D-Link DGS-3324SR Layer 3 Stackable Gigabit Ethernet Switch
Version No.
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:
Version No.
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
Link-State Request Packet
3
Router ID
Area ID
Checksum
Authentication
Authentication
Link-State Type
Link-State ID
Advertising Router
Link-State Update Packet
4
Router ID
Area ID
Checksum
Authentication
Authentication
Number of Advertisements
Link-State Advertisements ...
Packet Length
Authentication Type
Packet Length
Authentication Type
105