D-Link xStack Reference Manual page 215

®
xStack DGS-3620 Series Layer 3 Managed Stackable Gigabit Switch Web UI Reference Guide
A router that sends a Link-State Request packet has in mind the precise instance of the database pieces it is
requesting, defined by LS sequence number, LS checksum, and LS age, although these fields are not specified in
the Link-State Request packet itself. The router may receive even more recent instances in response.
The format of the Link-State Request packet is shown below:
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.
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 Request Packet
3
Checksum
Advertising Router
Figure 6-32 Link-State Request Packet
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
Link-State Type
Link-State ID
214