ZyXEL Communications XGS-4526 사용자 설명서

Chapter 37 OSPF

XGS-4526/4528F/4728F User’s Guide

The following table describes the four classes of OSPF routers.

The following figure depicts an OSPF network example. The backbone is area 0 
with a backbone router. The internal routers are in area 1 and 2. The area border 
routers connect area 1 and 2 to the backbone. 

Figure 159   OSPF Network Example 

Layer-3 devices exchange routing information to build a synchronized link state 
database within the same AS or area. The link state database contains records of 
router IDs, their associated links and path costs. Each device can then use the link 
state database and Dijkstra algorithm to compute the least cost paths to network 
destinations. 

Layer-3 devices build a synchronized link state database by exchanging Hello 
messages to confirm which neighbor (layer-3) devices exist and then they 
exchange database descriptions (DDs) to create the link state database. The link 
state database is constantly updated through LSAs (Link State Advertisements). 

An OSPF interface is a link between a layer-3 device and an OSPF network. An 
interface has state information, an IP address and subnet mask associated with it. 

Table 114   OSPF: Router Types 

Internal Router (IR)

An Internal or intra-area router is a router in an area.

Area Border Router 
(ABR)

An Area Border Router connects two or more areas.  

Backbone Router (BR)

A backbone router has an interface to the backbone. 

AS Boundary Router

An AS boundary router exchanges routing information with 
routers in other ASs.