Well, that's way off. We'll never get faster than that. We've got gigabit ethernet, we've got 10 gigabit ethernet, and we've even got 40 gigabit and gigabit ethernet now. Using the old default reference bandwidth, it'll all be treated the same equal cost by OSPF. We want to set the reference bandwidth to a higher volume.
The way you do that is at the global config, we issue the commands:. If you set it to for example, that would mean that gigabit ethernet interfaces would have a cost of one, fast ethernet would get a cost of But you want to think a bit further ahead in the future. If on your current production network, your fastest interfaces right now are gigabit ethernet, don't set a reference bandwidth of because maybe in a year or two's time, you're going to have 10 gigabit, 40 gigabit ethernet, and gigabit ethernet.
Set it to a high value that you're not going to have to change it again in the future. When you set the reference bandwidth, you need to do it the same on all routers so they're all using a consistent metric.
In the example here, I've set the reference bandwidth to , which is gigabit ethernet. The fast ethernet interface along the top path will get a cost of , the gigabit ethernet interfaces along the bottom path, get a cost of Now, it will prefer the bottom path because we changed the reference bandwidth.
In real-world networks, typically all you'll have to do is just change the reference bandwidth and then OSPF is going to automatically select the highest bandwidth paths, which is what you would normally prefer. However, you might want to manipulate this. For example, say you've got a high latency satellite link, which has higher bandwidth, but you want to prefer the lower bandwidth interface.
You can do that by manipulating the OSPF metric. Another reason would be just if you want to spread the load of your traffic across the different paths in your network. So, OSPF takes the bandwidth of an interface into account when calculating the metric so paths along higher bandwidth links will be preferred.
Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.
Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information. We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way.
Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.
All rights reserved. Cisco Press. Join Sign In. Date: Dec 3, In particular, this chapter discusses the theory behind types of routing protocols, including distance vector and link-state logic. Both OSPF and EIGRP cause each router to process its topology database, from which the router can choose the currently best route lowest metric route to reach each subnet, adding those best routes to the IPv4 routing table.
Topology Information and LSAs Routers using LS routing protocols need to collectively advertise practically every detail about the internetwork to all the other routers. Overview Pearson Education, Inc. Collection and Use of Information To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including: Questions and Inquiries For inquiries and questions, we collect the inquiry or question, together with name, contact details email address, phone number and mailing address and any other additional information voluntarily submitted to us through a Contact Us form or an email.
Surveys Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Contests and Drawings Occasionally, we may sponsor a contest or drawing. Newsletters If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information ciscopress.
Service Announcements On rare occasions it is necessary to send out a strictly service related announcement. Customer Service We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form. Other Collection and Use of Information Application and System Logs Pearson automatically collects log data to help ensure the delivery, availability and security of this site.
Web Analytics Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. Cookies and Related Technologies This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Security Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.
Children This site is not directed to children under the age of Marketing Pearson may send or direct marketing communications to users, provided that Pearson will not use personal information collected or processed as a K school service provider for the purpose of directed or targeted advertising.
Such marketing is consistent with applicable law and Pearson's legal obligations. Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
OSPF provides support for discontiguous networks because every area has a collection of networks, and OSPF attaches a mask to each advertisement. OSPF sends all advertisements using multicast addressing. The offset-list command does not work for OSPF.
OSPF generates a default only if it is configured using the command default-information originate and if there is a default network in the box from a different process. The default route in OSPF is 0. If you want an OSPF-enabled router to generate a default route even if it does not have a default route itself, use the command default-information originate always.
The distribute-list in command only filters routes from entering the routing table; it does not prevent link-state packets from being propagated. Therefore, this command does not help conserve router memory, and it does not prohibit a router from propagating filtered routes to other routers. Caution: Use of the distribute-list in command in OSPF may lead to routing loops in the network if not implemented carefully.
It can be applied to external type 2 and external type 1 routes, but not to intra-area and interarea routes. Refer to configuration example of distribute-list in OSPF,. This rule of preference cannot be changed. However, it applies only within a single OSPF process. If a router is running more than one OSPF process, route comparison occurs. With route comparison, the metrics and administrative distances if they have been changed of the OSPF processes are compared.
Route types are disregarded when routes supplied by two different OSPF processes are compared. If you are not using a fully meshed SMDS cloud, you must use the ip ospf network point-to-multipoint command. The SPF metrics are preserved. The redistribution between them is like redistribution between any two IP routing processes. You can configure OSPF to understand whether it should attempt to use multicast facilities on a multi-access interface.
Also, if multicast is available, OSPF uses it for its normal multicasts. You can use subinterfaces with Frame Relay to tie together a set of virtual circuits VCs to form a virtual interface, which acts as a single IP subnet.
All systems within the subnet should be fully meshed. When an unnumbered interface is configured, it references another interface on the router. When enabling OSPF on the unnumbered interface, use the address-wild-mask pair of interfaces to which the unnumbered interface is pointing.
No, OSPF does not work if you have one side numbered and the other side unnumbered. This creates a discrepancy in the OSPF database that prevents routes from being installed in the routing table.
To correct the problem, configure a loopback interface. Your software may not support OSPF. This error message occurs most frequently with the Cisco series routers.
DR means designated router. BDR means backup designated router. The formula to calculate the cost is reference bandwidth divided by interface bandwidth. Note: If ip ospf cost cost is used on the interface, it overrides this formulated cost. The OSPF metric for a route is the sum of the interface costs for all outgoing interfaces in the route. By default, a router's OSPF interface cost is actually derived from the interface bandwidth: The faster the bandwidth, the lower the cost.
Why we use OSPF? The idea behind the OSPF areas is to lower the amount of routing traffic and lower the processing of your core routers. OSPF is link state routing protocol and you can tune a link state routing protocol to converge fast. To specify the cost of sending a packet on an interface, use the ip ospf cost command. To reset the path cost to the default, use the no form of this command. What is the metric for RIP? The hop count 0 denotes a network that is directly connected to the router.
0コメント