Router Type
Routers are classified into the following types according to their locations in the AS:
l
Internal routers
l
Area border routers (ABRs)
l
Backbone routers
l
AS boundary routers (ASBRs)
Figure 5-2
Types of routers
Area3
Area0
Area1
Area2
Area4
Internal
Router
ABR
Backbone
Router
ASBR
OSPF Network Types
OSPF classifies networks into four types according to the link layer protocol:
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Broadcast: If the link layer protocol is Ethernet or FDDI, OSPF defaults the network type
to broadcast. In this type of networks, the following situations occur.
–
Hello packets and packets from the Designated Router (DR) are sent in multicast mode
(224.0.0.5: indicates the reserved IP multicast addresses for OSPF devices).
–
Link State Update (LSU) packets are sent to the DR in multicast mode (224.0.0.6:
indicates the reserved IP multicast address for the OSPF DR), and the DR forwards the
LSU packets to destination 224.0.0.5.
–
Database Description (DD) packets, Link State Request (LSR) packets, and all
retransmission packets are sent in unicast mode.
–
Link State Acknowledgement (LSAck) packets are usually sent in multicast mode
(224.0.0.5). When a router receives repeated LSAs, or the LSAs are deleted due to the
timeout of the maximum lifetime, LSAck packets are sent in unicast mode.
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Non-Broadcast Multi-Access (NBMA): If the link layer protocol is Frame Relay, ATM, or
X.25, OSPF defaults the network type to NBMA. In this type of networks, protocol packets,
such as Hello packets, DD packets, LSR packets, LSU packets, and LSAck packet, are
transmitted in unicast mode.
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Point-to-Multipoint (P2MP): A P2MP network must be forcibly changed from other
network types. In this type of networks, Hello packets are transmitted in multicast mode
HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing
5 OSPF Configuration
Issue 02 (2014-09-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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