D-Link DGS-3627G Product Manual - Page 220

xStack® DGS-3600 Series Layer 3 Managed Gigabit Ethernet Switch Database Description packet 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 Version No. Type Packet Length Router ID Area ID Checksum Authentication Type Authentication Authentication Figure 4- 39. OSPF Packet Header Format Field Version No. Type Packet Length Router ID Area ID Checksum Authentication Type Authentication 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. 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: 204