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DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
Field Description
Version No. The OSPF version number
Type The OSPF packet type. The OSPF packet types
are as follows:
Type Description
1 Hello
2 Database Description
3 Link-State Request
4 Link-State Update
5 Link-State Acknowledgment
Packet Length The length of the packet in bytes. This length
includes the 24-byte header.
Router ID The Router ID of the packet’s source.
Area ID 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
Checksum A standard IP checksum that includes all of the
packet’s contents except for the 64-bit
authentication field.
Authentication Type The type of authentication to be used for the
packet.
Authentication A 64-bit field used by the authentication scheme.
Table 5-13. OSPF Packet Header
The 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 hello packets,
so that differences can inhibit the forming of neighbor relationships. A detailed explanation of the
receive processing for Hello packets, so that differences can inhibit the forming of neighbor
relationships.
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