D-Link xStack DGS-3120 Series Reference Manual page 194

xStack® DGS-3120 Series Layer 3 Managed Gigabit Ethernet Switch Web UI Reference Guide
Parameter
Version No.
Type
Packet Length
Router ID
Area ID
Checksum
Authentication Type
Authentication
Hello Packet
Hello packets are OSPF packet type 1. They are sent periodically on all interfaces, including virtual links, in order to
establish and maintain neighbor relationships. In addition, Hello Packets are multicast on those physical networks
having a multicast or broadcast capability, enabling dynamic discovery of neighboring routers.
All routers connected to a common network must agree on certain parameters such as the Network Mask, the Hello
Interval, and the Router Dead Interval. These parameters are included in the hello packets, so that differences can
inhibit the forming of neighbor relationships. A detailed explanation of the receive process for Hello packets is
necessary so that differences cannot inhibit the forming of neighbor relationships.
The format of the Hello packet is shown below:
Description
The OSPF version number.
The OSPF packet type. The OSPF packet types are as follows: Type Description Hello
Database Description Link-State Request Link-State Update Link-State
Acknowledgment.
The length of the packet in bytes. This length includes the 24-byte header.
The Router ID of the packet's source.
A 32-bit number identifying the area that this packet belongs to. All OSPF packets are
associated with a single area. Packets traversing a virtual link are assigned the
backbone Area ID of 0.0.0.0
A standard IP checksum that includes all of the packet's contents except for the 64-bit
authentication field.
The type of authentication to be used for the packet.
A 64-bit field used by the authentication scheme.
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