3Com CoreBuilder 3500, Implementation Manual

Page: 365 / 592

Key Concepts 365
Router IDs
The OSPF router ID identifies a router to other routers within an
autonomous system. OSPF uses three types of router identifiers, which
take the form of an IP address:
■
Default — An arbitrary ID that the system generates and uses as the
default router ID
■
Interface — The address of an IP interface on the router
■
Address — An arbitrary user-defined ID in the form of an IP address
You cannot set the router id to either 0.0.0.0 or 255.255.255.255.
Protocol Packets
The OSPF protocol uses these types of packets:
■
Hello packets — Router interfaces periodically transmit hello packets
to identify and maintain communications with their neighbors. In
nonmulticast networks, routers find neighbors by sending unicast
hello packets to other statically configured routers.
■
Database description packets — Neighbor routers use database
description packets to synchronize their link state summary databases.
■
Link state request packets — To collect network topology data,
routers transmit link state request packets to their neighbors on the
segment.
■
Link state update packets — On receiving a link state request
packet, a router floods packets containing its LSA data into the area or
autonomous system that it serves. The information contained in the
packets depends on the router’s location and function in the network.
■
Link state ack(nowledge) packets
— Routers use these packets to
acknowledge receipt of link state update packets.