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<v ->Troubleshooting network issues,</v>
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in this section,
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we're going to discuss how to troubleshoot general
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networking issues.
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As we go through this section of the course,
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we're going to again focus on Domain 5 network troubleshooting
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and our final objective,
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objective 5.5.
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Objective 5.5 states,
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that given a scenario,
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you must troubleshoot general networking issues.
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Now, as we go through this section of the course,
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we're going to talk about collisions, and broadcast storms,
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and duplicate addresses,
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and flooding and switching, and routing loops,
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DHCP issues, IP misconfigurations,
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VLM misconfigurations, firewall issues, DNS issues,
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NTP issues, network performance issues,
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low optical link budgets,
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certificate issues,
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licensed feature issues, BYOD challenges,
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and some hardware failures.
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But before we cover all those different issues
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in this section of the course,
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I want to use the rest of this lesson
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to discuss a few things you need to consider
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during your general network troubleshooting efforts,
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including device configuration reviews,
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routing tables, interface status,
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VLAN assignments,
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and your network performance baselines.
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First, we have device configuration reviews.
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Now previously
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we've gone through a standard device configuration
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and we reviewed it section by section.
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But here, I just wanted to remind you
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that whenever you're experiencing a networking issue,
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it's always a good idea
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to look at your configuration files once more.
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Most network devices have two configurations,
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a startup configuration and a running configuration.
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The startup configuration file is stored in NVRAM,
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and it contains the commands needed
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to initially configure a router
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when it's being booted up.
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It also creates the running configuration file
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that's going to to be stored in RAM
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and used during normal operations.
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The running configuration
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is the configurations that are actively
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being used by the router
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at any given time.
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Any changes made to the configuration
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by a network technician
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in the command line interface
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is applied first to the running configuration.
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But,
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if it doesn't saved back to the startup configuration,
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those changes will be lost
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the next time you reboot the router.
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So if everything was working and you rebooted the router
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and things stop working,
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it may be that you're missing a configuration.
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Now if you want to see the startup configuration,
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you can enter the command, Show startup-config
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at the command line interface.
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If you want to see the running configuration,
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you're going to enter show running-config
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at the command line interface.
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Now if you need to save any changes
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that you've made to the running config,
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to the startup config,
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you can do this by entering the command;
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copy running-config, startup-config
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into the command line interface.
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Remember
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these three commands work on Cisco devices,
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but other network devices use similar commands
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to conduct these same types of actions.
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Now, next, you need to look at your routing tables.
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Anytime data isn't flowing properly in your networks,
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it could be a routing issue
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to verify your routing tables.
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You need to check your routers,
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your layer three switches
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and any workstations or servers you may have
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to view the routes on a network device
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like a router or a layer three switch.
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You can enter the command Show IP route
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from the command line interface.
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Now, if you need a view, the routing table
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on a Windows, workstation or server,
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you can use the command Route print at the command prompt.
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If you need to display the routing table on a Linux
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Unix or OSX workstation or server,
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you can enter the command Route-N at the shell.
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Next, you should look at the interface status itself
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when there's networking issues going on
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to do this, you're going to enter the show interface
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or show interfaces command
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at the prompt within the command line environment
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of your router or switch
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again, this is a Cisco specific command,
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but similar commands exist for other brands
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of network devices.
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From this interface status,
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we're going to be able to determine all sorts of issues,
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such as duplexing issues, DHCP issues, collisions,
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and broadcast storms.
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Next, we can check the VLAN assignments being used
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for our network and our devices,
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the VLAN assignments or VLAN tagging
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is the practice of segmenting an organizational network
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and separating users into respective networks Sections
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based on their roles and responsibilities.
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Most commonly
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VLAN assignments are done using static assignments
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based on the ports and the interfaces being used.
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Conversely,
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you can also set up dynamic VLAN assignments
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based on a Mac address of a given client.
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And that way, when that client connects,
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it will be put into the right VLAN,
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regardless of which physical port it's being connected to,
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to use dynamic VLAN configurations though,
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you need to use a VLAN Membership Policy Server or VMPS.
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As well as a client server and database.
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Now, remember,
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If you're using VLANs,
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these will be things that will break up
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your broadcast domains
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and reduce the chance of a broadcast on from occurring.
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But because these VLANs break up broadcast domains,
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you need to route traffic from one VLAN to another,
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using a router or layer three switch.
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If you forget to include a router in your network
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architecture
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and you're using VLANs,
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your traffic is not going to be able to flow
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between those VLANs.
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So make sure you keep this in mind.
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Finally,
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you need to ensure that you have
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a good network performance baseline
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created for your network after you initially configure it
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in the simplest terms,
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a network performance baseline,
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it's just a set of metrics used
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in network performance monitoring
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to define what the normal working conditions
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of this enterprise network infrastructure
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are going to look like.
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Engineers are going to use network performance baselines
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for comparison
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to catch changes in traffic that could indicate
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there's a problem with your network.
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It also lets networks operations personnel
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like network technicians,
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understand the before and after effects.
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Whenever a change is made,
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this makes it easier to measure the benefit
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and calculate a return on investment
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when you're making network changes.
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Basically,
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if you think there's a problem
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and something looks abnormal,
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you should consult your network baseline
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to see if there really is something that's wrong
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or something that's been changed.
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And how large of a change has caused
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on your performance.
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Because if you change one thing by adding a route
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and your network performance went down by 50%,
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you probably don't want to add that route anymore.
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And so you need to look into that closer
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again there's lots of places and lots of things
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that can go wrong in our networks.
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So with all these considerations in mind,
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let's jump into this section
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on troubleshooting network issues.
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(upbeat music)