Home > Articles > Cisco Network Technology > General Networking > Five Crucial Commands for Verifying Cisco Switch Network Status and Operational State

Five Crucial Commands for Verifying Cisco Switch Network Status and Operational State

  • Date: Aug 11, 2015.

Contents

  1. Five Crucial Commands for Verifying Cisco Switch Network Status and Operational State

Article Description

A network engineer needs to be conscious of the state of the network and every device connected to it. But when your network consists of multiple devices connected at a distance, how can you test connections and keep on top of network performance? Sean Wilkins, co-author of CCNA Routing and Switching 200-120 Network Simulator, discusses five basic commands you need to know and use correctly to maintain your Cisco network.

Like this article? We recommend

CCNA Routing and Switching 200-120 Network Simulator

CCNA Routing and Switching 200-120 Network Simulator

$149.99

Overview

For Cisco (and many other vendors), new commands are introduced at each progressive level of system verification. This article looks at five essential commands used to verify a network switch’s status and operation:

  • ping
  • traceroute
  • telnet
  • ssh
  • show cdp neighbors

ping

Available on almost all operating system platforms, including Cisco IOS, the ping command is used to verify the reachability of a targeted device. It does this by sending an Internet Control Message Protocol (ICMP) echo message to the target; if the target receives the message (and is not configured to drop it), it responds to the initial sender with an ICMP echo-reply message. In a perfect world, with no firewalls, and all devices configured to respond to these messages, the ping command would work perfectly. However, many devices (or devices en route, like firewalls) are purposely configured to ignore ICMP echo messages automatically, in order to hide their existence and avoid being targeted by attackers. In these cases, engineers must decide whether the unsuccessful ping is a real problem or a purposeful part of a network’s design.

Cisco IOS also has an extended version of the ping command that allows for more complex command configurations. For example, an engineer has the ability to control the source IP used (which makes sense when being run from a router configured with multiple IP addresses), the size of the messages being sent, and the content of the messages, among other options.

traceroute

The traceroute command is typically used along with the ping command to further determine the reachability of a destination. traceroute works a bit differently from ping; instead of simply sending a message to the destination directly, it aims to find the path from the source to the target destination. It does this by using either ICMP echo messages on Windows or the User Datagram Protocol (UDP) probe messages on Linux and Cisco IOS. It figures out the path by taking advantage of the IP Time to Live (TTL) field.

It’s important to understand what the TTL field does. In normal circumstances, the TTL is used as a loop-prevention mechanism; it works by being set to a number which is then decremented at every respective IP “’hop.” If the TTL reaches a device and is decremented to 0, the packet is dropped and an ICMP “destination unreachable” message is sent back to the source device. When used by the traceroute command, the TTL finds each of the hops in the path between the source and the destination:

  1. Initially the source sends an ICMP or UDP message to the destination with a TTL of 1.
  2. When the packet reaches the first hop, the TTL is decremented to 0; the device drops the packet and sends back an ICMP “destination unreachable” message.
  3. To find the second hop, the TTL is set to 2, for the third hop it’s set to 3, and so on; typically three packets are sent for each step toward the destination (three with a TTL set to 1, three with a TTL set to 2, and so on).
  4. These ICMP “destination unreachable” messages are received by the running traceroute command and interpreted into a readable output showing the path toward the destination.

As with the ping command, many organizations block the ICMP echo messages and some of the UDP messages; and the output should be read with this fact in mind.

The traceroute command on Cisco IOS is extended in the same way as the ping command variant that allows for extended command configurations. The options offered by traceroute mirror most of the options available in an extended ping.

telnet

The telnet command has been around for a long time, allowing users to manage devices via a command-line interface. Its very simple operation provides an unsecured Transmission Control Protocol (TCP) session between the source and destination. Characters entered on the source are immediately relayed to the destination, providing an experience on Cisco IOS (and Linux) that is the same as if the user were directly connected into the device locally.

The telnet command uses TCP port 23.

ssh

The ssh (secure shell) command works similarly to the telnet command but creates a secure communications channel between source and destination. This means that the username and password are not sent in clear text and are protected (at least to some level) from anyone listening in on the conversation.

The ssh command uses TCP port 22.

show cdp neighbors

The show cdp neighbors command is used on a Cisco IOS device to view neighboring devices discovered by the Cisco Discovery Protocol (CDP). CDP is a Cisco proprietary protocol used for Layer 2 discovery; it has the ability to discover all other supporting CDP devices on a shared segment. (It doesn’t work across Layer 3 devices.) The following example shows some typical output of this command:

R1#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
                  D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
R2               Fas 0/0            172              R    7206VXR   Fas 0/0
R1#

In this example, we learn that the remote device (R2) is connected via R1’s FastEthernet0/0 interface and is connected to R2’s FastEthernet0/0 interface, and R2 is a Cisco 7206VXR router. This information is very helpful when mapping out unfamiliar networks. It can also be used to help ensure that a device is connected to the correct remote device(s) on the correct interface; as engineers often must configure devices remotely, this command is useful when installing new equipment, to ensure that physical interfaces are connected to the appropriate networks.

Keep in mind that CDP is a proprietary protocol and will not work to discover most other non-Cisco devices; this command is enabled by default on Cisco devices. A standards-based alternative to CDP is the Link Layer Discovery Protocol (LLDP)—IEEE 802.1AB, which is supported by many other vendors, but is not enabled by default on Cisco devices.

Summary

This article covers some of the most important basic commands you will need to know in order to verify status and current operational state of a network switch. You are likely to use these commands often. Engineers at every level must know these commands and be familiar with how they work.

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