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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  TCP/IP Routing Protocols (Gateway Protocols)
                9  TCP/IP Interior Routing Protocols (RIP, OSPF, GGP, HELLO, IGRP, EIGRP)
                     9  Open Shortest Path First (OSPF)

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OSPF Hierarchical Topology, Areas and Router Roles
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OSPF General Operation and Message Types
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OSPF Route Determination Using SPF Trees
(Page 4 of 4)

Shortest Path Tree and Route Calculation Results

In this simple example, we only need three levels to construct the tree for RC (we would need more for RA or RD, however.) The final results would be the tree in Figure 183, and the routing information for RC to the four networks that is shown in Table 125.


Figure 183: OSPF Calculated Shortest Path First Tree

This is a graphical representation of the SPF tree calculated in Figure 182, showing only the final results of the calculation process.

 



Table 125: Example Calculated OSPF Routes

Destination Network

Cost

Next Hop

N1

5

RA

N2

3

(local)

N3

6

(local)

N4

10

RD


This of course is what you would expect in this very simple example. Note that there are no specific entries for other routers, since they are the “means to the end” of reaching networks. However, if one of the other routers were a boundary router that connected the AS to the outside world, there would be entries for the networks to which the boundary router connected, so RC knew to send traffic for those networks to that boundary router.


Previous Topic/Section
OSPF Hierarchical Topology, Areas and Router Roles
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Next Page
OSPF General Operation and Message Types
Next Topic/Section

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