Home > Articles > Cisco > CCDA

This chapter is from the book

Route Manipulation

This section covers PBR, route summarization, and route redistribution. You can use PBR to modify the next hop of packets from what is selected by the routing protocol. PBR is useful when the traffic engineering of paths is required. Routes are summarized to reduce the size of routing tables and at network boundaries. Redistribution between routing protocols is required to inject route information from one routing protocol to another. The CCDA must understand the issues with the redistribution of routes.

PBR

You can use PBR to modify the next-hop address of packets or to mark packets to receive differential service. Routing is based on destination addresses; routers look at the routing table to determine the next-hop IP address based on a destination lookup. PBR is commonly used to modify the next-hop IP address based on the source address. You can also use PBR to mark the IP precedence bits in outbound IP packets so that you can apply quality-of-service (QoS) policies. In Figure 12-9, Router A exchanges routing updates with routers in the WAN. The routing protocol might select Serial 0 as the preferred path for all traffic because of the higher bandwidth. The company might have business-critical systems that use the T1 but does not want systems on Ethernet 1 to affect WAN performance. You can configure PBR on Router A to force traffic from Ethernet 1 out on Serial 1.

Figure 12-9

Figure 12-9 Policy-Based Routing

Route Summarization

Large networks can grow very quickly from 500 routes to 1000, to 2000, and so on. Network IP addresses should be allocated to allow for route summarization. Route summarization reduces the amount of route traffic on the network and unnecessary route computation. Route summarization also allows the network to scale as a company grows.

The recommended location for route summarization is to summarize at the distribution layer of the network topology. Figure 12-10 shows a hierarchical network. It has a network core, regional distribution routers, and access routes for sites.

Figure 12-10

Figure 12-10 Route Summarization

All routes in Brazil are summarized with a single 10.1.0.0/16 route. The North America and European routes are also summarized with 10.2.0.0/16 and 10.3.0.0/16, respectively. Routers in Europe only need to know the summarized route to get to Brazil and North America, and vice versa. Again, design best practices are to summarize at the distribution toward the core. The core only needs to know the summarized route of the regional areas.

Route Redistribution

You configure the redistribution of routing protocols on routers that reside at the Service Provider Edge of the network. These routers exchange routes with other autonomous systems. Redistribution is also done on routers that run more than one routing protocol. Here are some reasons to do redistribution:

  • Migration from an older routing protocol to a new routing protocol.
  • Mixed-vendor environment in which Cisco routers might be using EIGRP and other vendor routers might be using OSPF.
  • Different administrative domain between company departments using different routing protocols.
  • Mergers and acquisitions in which the networks initially need to communicate. In this example two different EIGRP processes might exist.

Figure 12-11 shows an example of the exchange of routes between two autonomous systems. Routes from AS 100 are redistributed into BGP on Router A. Routes from AS 200 are redistributed into BGP on Router B. Then, Routers A and B exchange BGP routes. Router A and Router B also implement filters to redistribute only the desired networks.

Figure 12-11

Figure 12-11 Redistribution of BGP Routes

A company might also acquire another company that might be running another routing protocol. Figure 12-12 shows a network that has both OSPF and EIGRP routing protocols. Routers A and B perform redistribution between OSPF and EIGRP. Both routers must filter routes from OSPF before redistributing them into EIGRP and filter routes from EIGRP before redistributing them into OSPF. This setup prevents route feedback.

Figure 12-12

Figure 12-12 Redistribution Between IGPs

Route feedback occurs when a routing protocol learns routes from another routing protocol and then announces the routes to the other routing protocol. In Figure 12-12, OSPF should not announce the routes it learned from EIGRP, and EIGRP should not announce the routes it learned from OSPF.

You can use access lists, distribution lists, and route maps when redistributing routes. You can use these methods to specify (select) routes for redistribution, to set metrics, or to set other policies for the routes. They are also used to control routes' redistribution direction. Redistribution can be accomplished by two methods:

  • Two-way redistribution
  • One-way redistribution

In two-way redistribution, routing information is exchanged between both routing protocols. No static routes are used in this exchange. Route filters are used to prevent routing loops. Routing loops can be caused by one route protocol redistributing routes that were learned from a second route protocol back to that second routing protocol.

One-way redistribution only allows redistribution from one routing protocol to another. Normally it is used in conjunction with a default or static route at the edge of a network. Figure 12-13 shows an example of one-way redistribution. The routing information from the WAN routes is redistributed into the campus. But campus routes are not redistributed out to the WAN. The WAN routers use a default gateway to get back to the campus.

Figure 12-13

Figure 12-13 One-Way Route Redistribution

Other locations for one-way redistribution are from building access networks, BGP routes or static routes into the IGP, and from VPN static routes into the IGP.

Default Metric

There is a default metric of 0 when redistributing routes into RIPv2, IS-IS, and EIGRP. You should configure the metric of the redistributed routes to a metric other than 0. You can configure the metric in the redistribution command or configure a default metric. You can also use the command in OSPF. IS-IS does not use the default-metric command. The default-metric command has the following syntax for EIGRP:

   default-metric bandwidth delay reliability load mtu

OSPF Redistribution

This subsection reviews a few things you need to remember when designing a network that will redistribute with OSPF.

When redistributing routes into OSPF, use the subnets keyword to permit subnetted routes to be received. If you do not use it, only the major network route is redistributed, without any subnetworks. In other words, OSPF performs automatic summarization to IP classful network values.

By default, redistributed routes are classified as external Type 2 (E2) in OSPF. You can use the metric-type keyword to change the external route to an external Type 1 (E1). The network design can take into account the after-redistribution cost (Type 2) or the after-redistribution cost plus the path's cost (Type 1).

In Figure 12-14, Router B is configured to perform mutual redistribution between EIGRP 100 and OSPF process ID 50. In this example, you can use route maps and access lists to prevent routing loops. The route maps permit or deny the networks that are listed in the access lists. The subnets keyword redistributes every subnet in EIGRP into OSPF. This book does not cover exact configurations.

Figure 12-14

Figure 12-14 OSPF and EIGRP Redistribution

Pearson IT Certification Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Pearson IT Certification and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Pearson IT Certification products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

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. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

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. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

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. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

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. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

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 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 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.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.pearsonitcertification.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. 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.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


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.

Last Update: November 17, 2020