D-Link TM DES-6500, Руководство пользователя

Страница: 156 / 353

xStack DES-6500 Modular Layer 3 Chassis Ethernet Switch User Manual
Link-State Request packet
•
•
•
Link-State Update packet
Link-State Acknowledgment packet
OSPF Packet Header
Every OSPF packet is preceded by a common 24-byte header. This header contains the information necessary for a receiving
router to determine if the packet should be accepted for further processing.
The format of the OSPP packet header is shown below:
OSPF Packet Header
Type Packet Length
Router ID
Area ID
Checksum
Authentication Type
Authentication
Authentication
Version No.
Figure 6- 121. OSPF Packet Header Format
Field Description
Version No. The OSPF version number
Type
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
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.
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 can inhibit
the forming of neighbor relationships.
The format of the Hello packet is shown below:
141