D-Link DGS-3650 Product Manual - Page 223
Link-State Update Packet, Link-State Acknowledgment Packet, Link-State Request Packet
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xStack® DGS-3600 Series Layer 3 Managed Gigabit Ethernet Switch Link-State Request Packet Version No. 3 Packet Length Router ID Area ID Checksum Authentication Type Authentication Authentication Link-State Type Link-State ID Advertising Router Figure 4- 42. 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: Link-State Update Packet Version No. 4 Packet Length Router ID Area ID Checksum Authentication Type Authentication Authentication Number of Advertisements Link-State Advertisements ... Figure 4- 43. Link-State Update Packet 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. 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 LinkState Acknowledgment packets. Multiple link-state advertisements can be acknowledged in a single Link-State Acknowledgment packet. 207