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 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)

OSPF Hierarchical Topology, Areas and Router Roles 1 2 3 4 OSPF General Operation and Message Types

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.

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.

OSPF Hierarchical Topology, Areas and Router Roles 1 2 3 4 OSPF General Operation and Message Types