Link-state update packet – Allied Telesis AT-9724TS User Manual

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Figure 6- 103. 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:

Figure 6- 104. 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.

111

Allied Telesyn AT-9724TS High-Density Layer 3 Stackable Gigabit Ethernet Switch

Octets

OSPF Link-State Request Packet

Router ID

Area ID

Checksum

Authentication Type

Authentication

Link-State ID

Advertising Router

Link-State Type

Version No.

Packet Length