Home > Articles > Cisco Network Technology > General Networking > Cisco Networking Academy's Introduction to Routing Concepts

Cisco Networking Academy's Introduction to Routing Concepts

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Mar 20, 2014.

Chapter Description

This chapter introduces and explains the primary functions and features of a router and explains the process for connecting and configuring devices to the router. It continues by describing the process by which routers manage packets, determine data paths, and build routing tables.

Verify Connectivity of Directly Connected Networks (1.1.4)

The first task to undertake once the basic settings and interfaces are configured is to verify and validate the configured settings. This is an important step and should be done before any other configurations are added to the router.

Verify Interface Settings (1.1.4.1)

There are several show commands that can be used to verify the operation and configuration of an interface. The following three commands are especially useful to quickly identify an interface status:

  • show ip interface brief: Displays a summary for all interfaces, including the IPv4 address of the interface and current operational status.
  • show ip route: Displays the contents of the IPv4 routing table stored in RAM. In Cisco IOS 15, active interfaces should appear in the routing table with two related entries identified by the code 'C' (Connected) or 'L' (Local). In previous IOS versions, only a single entry with the code 'C' will appear.
  • show running-config interface interface-id: Displays the commands configured on the specified interface.

Figure 1-17 displays the output of the show ip interface brief command.

Figure 1-17

Figure 1-17 Display Interface Summaries

The output reveals that the LAN interfaces and the WAN link are all activated and operational as indicated by the Status of “up” and Protocol of “up.” A different output would indicate a problem with either the configuration or the cabling.

Figure 1-18 displays the output of the show ip route command.

Figure 1-18

Figure 1-18 Verify the IPv4 Routing Table

Notice the three directly connected network entries and the three local host route interface entries. A local host route has an administrative distance of 0. It also has a /32 mask for IPv4, and a /128 mask for IPv6. The local host route is for routes on the router owning the IP address. It is used to allow the router to process packets destined to that IP.

Figure 1-19 displays the output of the show running-config interface command. The output displays the current commands configured on the specified interface.

Figure 1-19

Figure 1-19 Verify an Interface Configuration

The following two commands are used to gather more detailed interface information:

  • show interfaces: Displays interface information and packet flow count for all interfaces on the device
  • show ip interface: Displays the IPv4-related information for all interfaces on a router

Verify IPv6 Interface Settings (1.1.4.2)

The commands to verify the IPv6 interface configuration are similar to the commands used for IPv4.

The show ipv6 interface brief command in Figure 1-20 displays a summary for each of the interfaces.

Figure 1-20

Figure 1-20 Verify the R1 IPv6 Interface Status

The “up/up” output on the same line as the interface name indicates the Layer 1/Layer 2 interface state. This is the same as the Status and Protocol columns in the equivalent IPv4 command.

The output displays two configured IPv6 addresses per interface. One address is the IPv6 global unicast address that was manually entered. The other address, which begins with FE80, is the link-local unicast address for the interface. A link-local address is automatically added to an interface whenever a global unicast address is assigned. An IPv6 network interface is required to have a link-local address, but not necessarily a global unicast address.

The show ipv6 interface gigabitethernet 0/0 command output shown in Figure 1-21 displays the interface status and all of the IPv6 addresses belonging to the interface. Along with the link-local address and global unicast address, the output includes the multicast addresses assigned to the interface, beginning with prefix FF02.

Figure 1-21

Figure 1-21 Verify the IPv6 Configuration on R1 G0/0

The show ipv6 route command shown in Figure 1-22 can be used to verify that IPv6 networks and specific IPv6 interface addresses have been installed in the IPv6 routing table. The show ipv6 route command will only display IPv6 networks, not IPv4 networks.

Figure 1-22

Figure 1-22 Verify the R1 IPv6 Routing Table

Within the routing table, a ‘C’ next to a route indicates that this is a directly connected network. When the router interface is configured with a global unicast address and is in the “up/up” state, the IPv6 prefix and prefix length is added to the IPv6 routing table as a connected route.

The IPv6 global unicast address configured on the interface is also installed in the routing table as a local route, as indicated with an ‘L’ next to the route entry. The local route has a /128 prefix. Local routes are used by the routing table to efficiently process packets with the interface address of the router as the destination.

The ping command for IPv6 is identical to the command used with IPv4 except that an IPv6 address is used. As shown in Figure 1-23, the ping command is used to verify Layer 3 connectivity between R1 and PC1.

Figure 1-23

Figure 1-23 Verify Connectivity on R1

Other useful IPv6 verification commands include:

  • show interface
  • show ipv6 routers

Filter Show Command Output (1.1.4.3)

Commands that generate multiple screens of output are, by default, paused after 24 lines. At the end of the paused output, the --More-- text displays. Pressing Enter displays the next line and pressing the spacebar displays the next set of lines. Use the terminal length number command to specify the number of lines to be displayed. A value of 0 (zero) prevents the router from pausing between screens of output.

Another very useful feature that improves the user experience in the command-line interface (CLI) is the filtering of show output. Filtering commands can be used to display specific sections of output. To enable the filtering command, enter a pipe (|) character after the show command and then enter a filtering parameter and a filtering expression.

The filtering parameters that can be configured after the pipe include:

  • section: Shows entire section that starts with the filtering expression
  • include: Includes all output lines that match the filtering expression
  • exclude: Excludes all output lines that match the filtering expression
  • begin: Shows all the output lines from a certain point, starting with the line that matches the filtering expression

Figures 1-24 through 1-27 provide examples of the various output filters. The example in Figure 1-24 uses the pipe character and the section keyword.

Figure 1-24

Figure 1-24 Filter show Commands by Section

Figure 1-25

Figure 1-25 Filter show Commands by Common Keyword

Figure 1-26

Figure 1-26 Filter show Commands to Exclude Rows of Output

Figure 1-27

Figure 1-27 Filter show Commands Beginning from a Keyword

The example in Figure 1-25 uses the pipe character and the include keyword.

The example in Figure 1-26 uses the pipe character and the exclude keyword.

The example in Figure 1-27 uses the pipe character and the begin keyword.

Command History Feature (1.1.4.4)

The command history feature is useful, because it temporarily stores the list of executed commands to be recalled.

To recall commands in the history buffer, press Ctrl+P or the Up Arrow key. The command output begins with the most recent command. Repeat the key sequence to recall successively older commands. To return to more recent commands in the history buffer, press Ctrl+N or the Down Arrow key. Repeat the key sequence to recall successively more recent commands.

By default, command history is enabled and the system captures the last 10 command lines in its history buffer. Use the show history privileged EXEC command to display the contents of the buffer.

It is also practical to increase the number of command lines that the history buffer records during the current terminal session only. Use the terminal history size user EXEC command to increase or decrease the size of the buffer.

For example, the following displays a sample of the terminal history size and show history commands:

R1# terminal history size 200
R1#
R1# show history
  show ip interface brief
  show interface g0/0
  show ip interface g0/1
  show ip route
  show ip route 209.165.200.224
  show running-config interface s0/0/0
  terminal history size 200
  show history
R1#
8. Routing Decisions (1.2) | Next Section Previous Section

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press 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 Cisco Press 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@ciscopress.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 Cisco 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.ciscopress.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