So we're going to continue on with our discussion of some of our more advanced OSPF topics and we're going to talk about OSPF Virtual Links. OSPF Virtual Links are not something that you really want to use in your network on purpose. They're something that you might have to use for whatever reason and we'll go over the most common reason for that here in just a little bit, but OSPF Virtual Links allow you to break the rules and oh boy, you're thinking alright, I love breaking rules. Well, it doesn't allow you to break all the rules, it allows you to break one of the rules of OSPF and that rule is, all areas must connect directly to Area 0. If you'll recall from our concepts video or from our introduction to OSPF. If your Area doesn't connect to Area 0 then, well it just won't work right, the routes won't propagate correctly, you won't have reliable communications back to the network that's separated from Area 0. It's, it's just a huge mess. However, if you can't connect an area directly to Area 0 you can tunnel the data through another area. Again it's not something you'd really want to plan for, it's not something you design on purpose but as we all know, the best laid plans of mice and men will always go awry. And sometimes you'll end up with a network that's designed like this. Now let's say that you have the corporate office up here and you have another area that's out here, say the corporate offices in North America and this is in Australia. Well let's say that one of the Australia offices or sub businesses or whatever buys another company and rather than run a WAN link directly from that company all the way back to the corporate office, well it's just easier to connect them to the existing office in Australia and that way, you know, well in theory you can just send the data through this Area 1 and get it to this other office down here, this Area 2. Right. No, I mean, it's technology not magic, it doesn't really work that way. Even though it looks logical that it should. Well this is exactly what Virtual Links were meant to handle and basically what Virtual Links allow you to do, is take the data from Area 2, tunnel it through Area 1 and basically have this ABR act like it's directly connected to this ABR so that the traffic from here goes through this Virtual Tunnel and drops out on Area 0. Therefore you're not breaking the rules anymore and life is happy and grand. And honestly the set up is not that difficult. We'll see it in the lab here in, in the next video where we discuss the Area Types and Virtual Links. I've bundled them all into, into one lab here. But again, the caveat is, is that the Virtual Link is dependent upon the Router ID and you'll recall from our discussion of Router IDs that you need to specify the Router ID or the Router ID would change and if the Router ID changes, if for example, the Router ID of this guy here changes, well this router here no longer can contact this Router ID on this IP address, so this tunnel fails, this whole network or this whole area of networks goes down and you really can't figure out why. Because again the only time that the Router ID changes is when the router's reloaded or OSPF is re-initialized. That's usually done off hours, so you reboot the router, you know, you upgrade the IOS or whatever, you reboot the router, okay, everything's up and good, I can talk to my areas. You completely forget about this area down here that was tunneled through. The next morning everyone here in Area 2 says, hey I can't get to the Mail Servers, I can't get out to the Internet, I can't get to A B or C Application. And you're running around with your hair on fire trying to figure out what happened. So I guess the cautionary tale of all this is, if you're going to use Virtual Links then you need to specify the Router IDs of all the routers involved. And you'll notice when we went through advanced lab, that on every router I set up I went and specified the Router ID. It's a good habit to get into because you never know when you're going to have something like this thrown at you. So anyway, as I've said, we'll see this in a lab, but I just wanted to at least go over what Virtual Links were, how they worked and give you the basic overview of them, which we've done and that concludes our overview of Virtual Links.
|Course:||Implementing Cisco IP Routing (642-902 ROUTE)|
|Duration:||10 hrs / 105 lessons|
|Captions:||Available on CD and Online University|
WIN XP SP3, OS X 6+, Android 4, iOS 4, Linux
TERMS & CONDITIONS OF USE
BY SUBSCRIBING TO THIS SERVICE, YOU ARE CONSENTING TO BE BOUND BY AND ARE BECOMING A PARTY TO THIS AGREEMENT, THE TERMS AND CONDITIONS OF WHICH SHALL PREVAIL IN GOVERNING YOUR RIGHTS OF USE. BY CLICKING THE "BECOME A MEMBER" BUTTON, THE INDIVIDUAL OR ENTITY LICENSING THE PRODUCT ("YOU") IS CONSENTING TO BE BOUND BY AND IS BECOMING A PARTY TO THIS AGREEMENT. IF LICENSEE DOES NOT AGREE TO ALL OF THE TERMS OF THIS AGREEMENT, THE BUTTON INDICATING "BECOME A MEMBER" MUST NOT BE SELECTED, AND LICENSEE MUST NOT INSTALL OR USE THE SOFTWARE.
"VTC" refers to Virtual Training Company,
"You" refers to the user or subscriber.
"Software" refers to the VTC training content and software.
2. LICENSE: VTC hereby grants to You a worldwide, non-royalty bearing, non-exclusive license to use the Software according to the provisions contained herein and subject to payment of the applicable subscription fees.
3. RESTRICTIONS: You may not do any of the following:
Save the Software to Your hard disk or other storage
medium; permit others to use the Software except as specified by addendum;
modify, reverse engineer, decompile, or disassemble the Software; make
derivative works based on the Software; publish or otherwise disseminate
the Software. VTC, Inc., VTC Online University, and the Virtual Training
Company site is owned and operated by VTC, Inc. as a corporation of
All materials on this site are the property of VTC unless otherwise specified. No material from these pages may be copied, reproduced, republished, downloaded, uploaded, posted, transmitted, or distributed in any way. Modification of the materials or use of the materials for any other purpose is a violation of U.S. copyright law and other proprietary rights. For purposes of this Agreement, the use of any such material on any other web site or networked computer environment is prohibited.
4. FEES: The rights granted under this Agreement
are effective only upon payment of the subscription fees, which are
strictly non-refundable other than as expressly provided herein. The
term "monthly subscription" is defined as any 30 day period.
The term "yearly subscription" is defined as one 365 day
period. A yearly subscription ends on the same numerical date as it
began (example July 28, 2004 to July 28, 2005).
The VTC Online University is access to every VTC training tutorial in our library. You pay a flat fee for access to these titles. You are billed according to your renewal selection below, and can renew monthly, yearly, or in any other increment offered. If you choose to be billed monthly, you will be billed every 30 days for the subscription until you request the subscription be cancelled. Our terms of service state that you must cancel a monthly subscription at least two business days before your renewal date. These two days give us enough time to ensure that you will not be charged again.
5. LIMITED WARRANTY: VTC warrants that the Software, if operated as directed, will substantially achieve the functionality described. VTC does not warrant, however, that Your use of the Software will be uninterrupted or that the operation of the Software will be error-free or secure. In addition, the security mechanisms implemented by the Software have inherent limitations, and You must determine that the Software sufficiently meets Your requirements. VTC also warrants that the media containing the Software, if provided by VTC, is free from defects in material from the date You acquired the Software. VTC's sole liability for any breach of this warranty shall be, in VTC's sole discretion: (i) to replace Your defective media or Software; or (ii) to advise You how to achieve substantially the same functionality with the Software as described; or (iii) if the above remedies are impracticable, to refund the subscription fee You paid for the Software. Only if You inform VTC of Your problem with the Software during the applicable subscription period will VTC be obligated to honor this warranty. VTC will use reasonable commercial efforts to repair, replace, advise, or refund pursuant to the foregoing warranty within thirty (30) days of being so notified. If any modifications are made to the Software by You during the warranty period; if the medium is subjected to accident, abuse, or improper use; or if You violate the terms of this Agreement, then this warranty shall immediately terminate. This warranty shall not apply if the Software is used on or in conjunction with hardware or software other than the unmodified version of hardware and software with which the Software was designed to be used as described.
THIS IS A LIMITED WARRANTY, AND IT IS THE ONLY WARRANTY MADE BY VTC OR ITS SUPPLIERS. VTC MAKES NO OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NONINFRINGEMENT OF THIRD PARTIES' RIGHTS. YOU MAY HAVE OTHER STATUTORY RIGHTS. HOWEVER, TO THE FULL EXTENT PERMITTED BY LAW, THE DURATION OF STATUTORILY REQUIRED WARRANTIES, IF ANY, SHALL BE LIMITED TO THE ABOVE LIMITED WARRANTY PERIOD. MOREOVER, IN NO EVENT WILL WARRANTIES PROVIDED BY LAW, IF ANY, APPLY UNLESS THEY ARE REQUIRED TO APPLY BY STATUTE NOTWITHSTANDING THEIR EXCLUSION BY CONTRACT. NO DEALER, AGENT, OR EMPLOYEE OF VTC IS AUTHORIZED TO MAKE ANY MODIFICATIONS, EXTENSIONS, OR ADDITIONS TO THIS LIMITED WARRANTY.
6. PROPRIETARY RIGHTS: VTC reserves all proprietary rights in and to the Software, is protected by copyright and other intellectual property laws and by international treaties. VTC, Inc.
Trademark Notice: VTC, Virtual Training Company,
Inc., The VTC Logo, and VTC Online University, are trademarks of VTC,
Inc. All other company and product names may be trademarks of their
The information contained herein is subject to change without notice. Copyright © 1995 - 2005 VTC, Inc. All rights reserved.
7. TERMINATION: This Agreement shall automatically terminate if You fail to comply with the restrictions described herein. Your obligations to pay outstanding subscription fees shall survive any termination of this Agreement.
8. LIMITATION OF LIABILITY: UNDER NO CIRCUMSTANCES
AND UNDER NO LEGAL THEORY, TORT, CONTRACT, OR OTHERWISE, SHALL VTC
OR ITS SUPPLIERS OR RESELLERS BE LIABLE TO YOU OR ANY OTHER PERSON
FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES OF
ANY CHARACTER, INCLUDING WITHOUT LIMITATION, DAMAGES FOR LOSS OF GOODWILL,
WORK STOPPAGE, COMPUTER FAILURE OR MALFUNCTION, OR ANY AND ALL OTHER
COMMERCIAL DAMAGES OR LOSSES. IN NO EVENT WILL VTC BE LIABLE FOR ANY
DAMAGES IN EXCESS OF THE AMOUNT VTC RECEIVED FROM YOU FOR A LICENSE
TO THE SOFTWARE, EVEN IF VTC SHALL HAVE BEEN INFORMED OF THE POSSIBILITY
DAMAGES, OR FOR ANY CLAIM BY ANY OTHER PARTY. THIS LIMITATION OF LIABILITY SHALL NOT APPLY TO LIABILITY FOR DEATH OR PERSONAL INJURY RESULTING FROM VTC'S NEGLIGENCE TO THE EXTENT APPLICABLE LAW PROHIBITS SUCH LIMITATION. SOME JURISDICTIONS DO NOT ALLOW THE EXCLUSION OR LIMITATION OF INCIDENTAL OR CONSEQUENTIAL DAMAGES, SO THIS EXCLUSION AND LIMITATION MAY NOT APPLY TO YOU.
9. Links To Other Materials: Linked sites found at the VTC site are not under the control of VTC, and we are not responsible for the content of any linked site or any link contained in a linked site. VTC may change links based solely on our discretion, and we reserve the right to terminate any link or linking program at any time. VTC does not, by linking to sites, endorse companies or products to which it links and reserves the right to note as such on its web pages. If you decide to access any of the third party sites linked to this site, you do this entirely at your own risk.
Forums, and Chat are not always screened by VTC, and we are not responsible for the content of any public or open forum content at the site. VTC may change these public forums based solely on our discretion, and we reserve the right to terminate any forum at any time. VTC does not, by allowing these forums, endorse companies or products which may be mentioned in these forums, and reserves the right to note as such on its web pages. If you decide to access any of the public forums in this site, or linked to this site, you do this entirely at your own risk.
9. GOVERNING LAW & DISPUTE RESOLUTION: This Agreement is governed by Virginia law. All disputes between You and VTC shall be finally resolved through arbitration in Winchester, Virginia. This site is controlled by VTC from its offices within the United States of America. VTC makes no representation that materials in the site are appropriate or available for use in other locations, and access to them from territories where their content is illegal is prohibited. Those who choose to access this site from other locations do so on their own initiative and are responsible for compliance with applicable local laws. You may not use or export the Materials in violation of U.S. export laws and regulations. Any claim relating to the Materials shall be governed by the internal substantive laws of the Commonwealth of Virginia, USA.
VTC may revise these Terms at any time by updating this posting. You should visit this page from time to time to review the then-current Terms because they are binding on you. Certain provisions of these Terms may be superseded by expressly designated legal notices or terms located on particular pages at this Site.
If you have any questions regarding this policy,
or your information specifically,
you may email us at:email@example.com.