Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Enjoy The TCP/IP Guide? Get the complete PDF!
The TCP/IP Guide

Custom Search







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)

Previous Topic/Section
OSPF Overview, History, Standards and Versions
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
OSPF Hierarchical Topology, Areas and Router Roles
Next Topic/Section

OSPF Basic Topology and the Link State Database (LSDB)
(Page 2 of 3)

OSPF Basic Topology and LSDB Example

For example, let's consider the same autonomous system we looked at in our examination of the RIP route determination algorithm. This internetwork has four individual networks, connected as follows:

  • Router A (RA) connects Network 1 (N1) to Network 2 (N2).

  • Routers B (RB) and C (RC) connect Network 2 to Network 3 (N3).

  • Router D (RD) connects Network 3 to Network 4 (N4).

To make this example more interesting, I am also going to add a direct link between RB and RC; the resulting AS is shown in Figure 179. The LSDB for this autonomous system would look something like Table 123.


Figure 179: Example OSPF Autonomous System

This is the same AS that we looked at in RIP (as shown in Figure 172), but with the addition of a link between the two routers RB and RC.

 



Table 123: Example OSPF Link State Database (LSDB)

To Router / Network

From Router

From Network

RA

RB

RC

RD

N1

N2

N3

N4

RA

 

 

 

 

0

0

 

 

RB

 

 

[

 

 

0

0

 

RC

 

[

 

 

 

0

0

 

RD

 

 

 

 

 

 

0

0

N1

[

 

 

 

 

 

 

 

N2

[

[

[

 

 

 

 

 

N3

 

[

[

[

 

 

 

 

N4

 

 

 

[

 

 

 

 


In practice, each of the bullets (“[“) in Table 123 would be replaced by a metric value indicating the cost to send a datagram from the particular router to another router or network. Note that the chart is symmetric, since if RB can reach RC, RC can reach RB. However, the costs do not have to be symmetric. It is possible for RB to have a metric that is higher for it to send to RC than for RC to send to RB.

Note also that there is no cost to reach a router from a network. This ensures that only one cost is “charged” for a router to send to another router over a network—the cost to reach the network from the router. This makes sense, since each router is a member of the network upon which it is connected.


Previous Topic/Section
OSPF Overview, History, Standards and Versions
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
OSPF Hierarchical Topology, Areas and Router Roles
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.