Figure 5-5 Roles Of Broadcast Interface - Raisecom ISCOM2600G-HI (A) Series Configuration Manual

Raisecom
ISCOM2600G-HI (A) Series Configuration Guide

Figure 5-5 Roles of broadcast interface

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OSPF packets
OSPF packets are divided into the following types:
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Only broadcast interfaces elect the DR. P2MP or P2P interfaces do not elect the
DR.
DR is a concept of a network segment and targeted for an interface on a router. A
router may be a DR for an interface and a BDR or DR Other for another interface.
The DR and BDR are elected by all routers in the same network segment through
Hello packets according to router priority and router ID. Devices with a priority
above 0 can be candidates for election. If priorities of two routers are the same,
the router with the larger router ID is preferential. Devices with priority of 0 cannot
be elected as the DR or BDR.
Router priority affects DR/BDR election. When election ends, a router with higher
priority may become effective for election. In this case, it does not replace the
elected DR/BDR, and has to wait for next DR/BDR election.
Hello packet: sent periodically, used to discover and maintain OSPF neighbor relations.
It carries timer values, DR, BDR, priority, and known neighbor information.
Database Description (DD) packet: used to synchronize database between two routers. It
describes abstract of each Link State Advertisement (LSA) in local LSDB, namely, LSA
packet header.
Link State Request (LSR) packet: used to request required LSA from the peer. After
exchanging DD packet, two routers learn the lack LSA for local LSDB compared to the
peer LSDB, and then send LSR packet to the peer to request required LSA. The content
is LSA abstract.
Link State Update (LSU) packet: used to send LSA required by the peer. The content is a
set of multiple LSAs.
Link State Acknowledgment (LSAck) packet: used to acknowledge received LSA. The
content is the header of the LSA to be acknowledged. An LSAck packet can
acknowledge multiple LSAs.
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