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This is one of a multiple land or local area network troubleshooting videos.
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In this video we have four switches running ingenious three switch one and switch two are configured
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as Layer three switches switch three and switch for configured as Layer two switches so I could change
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the symbol as an example
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to indicate that that's a layer to switch however these four switches are running.
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IOW a v layer to
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and what I've done is simply disable IP running on switch three and switch four.
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So we have four switches in the topology and two Iowa's v Rogers right a one and write it to acting
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as pieces.
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This is a very simple topology where we have a core and an access layer.
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Typically you would connect the core to the access layer using cross connects.
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I'm not going to do that in this troubleshooting video.
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Have a look in my CCN a course which is linked below for a more complex topology running HSR P optimized
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spanning tree redundancy between the core and the access layer and multiple other options.
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But this network will suffice for our basic troubleshooting.
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So now let's assume that a new hire has made some configuration changes on the network and users are
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complaining about network connectivity issues you've been told that to this user 10 1 to 1 in VLAN 2
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is unable to ping this user that has a P.C. with IP address 10 dot 1.0 3 or 2 in V land 3.
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You've been told that switch 3 is connected to switch 1 as follows.
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So each one is connected to switch 2 and switch 2 is connected to switch for but as Ronald Reagan said
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Trust but verify.
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And what I like to say is don't trust anything that you've been told about a network until you've checked
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it yourself.
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So you're not topology right a 1 is acting as P.S. 1 show IP interface brief shows us the IP address
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on the gigabit interface that looks right the IP address looks right subnet mask looks right.
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Let's see if we can ping 10 but wonder 3 or 2 which is the IP address of Rada t acting as P.S. To
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Okay so the ping is failing we don't seem to be able to ping that device so that piece of information
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is true.
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Show IP rot shows us no roots in the routing table but it shows us that the default gateway is set to
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tend on 1 2 2 5 4.
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Now that's because IP routing has been disabled on this Radha in this topology we've got Radha one acting
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as a P.C. so when IP writing is disabled this is what the writing table looks like.
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The default gateway has been configured on the P.C. so that's good.
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Let's check if we can ping the default gateway yes we can.
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Now where is the default gateway.
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We could try and Telnet to the default gateway
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and let's try and Telnet to the right type of address so the device is there.
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But we're told that a password is required but none is set.
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So hopefully the default gateway in this topology is either switch one or switch to which all of the
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core Layer 3 switches.
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So here's switch one show IP interface brief we can see that a villain one villain tune villain 3 have
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an IP address configured and that's the IP address on VLAN 2.
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So this should be the device that the P.C. is pinging.
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I'll do a debug IP ICMP on that switch and get to the P.C. to paying the default gateway.
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Now you need to be careful with debugging in a real world environment.
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Yeah.
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Because we studying for the CCMA we can simply enable any debug command because that'll help you learn
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the debug that are available but in the real world.
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Be careful with simply enabling a debug especially on a core device.
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You may get so much output on the console that you can't read anything or in a very bad situation the
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device may fall over so we don't want that.
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So in the real world.
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Be careful with debugging.
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Okay so the pings do arrive on this default gateway so that's good.
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I'm gonna turn off IP domain look up in the lab here to make things happen quicker.
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And then what we'll do is trace tendered one dot three or two which should be P.C. to an auto apology.
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Let's see how far it gets.
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So it gets to the default gateway which we've now determined is which one.
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So what we should do is update the documentation so we can say that these are the IP addresses on the
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V lands of that switch.
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That once again can be seen on switch one by using the show IP interface brief command and there they
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are once again
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the trace rot shows us that the traffic gets to the default gateway but then doesn't go anywhere else.
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Let's check if P.S. two components default gateway now a test I'd like to do is to make sure that the
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local device can ping the other VLAN of the default gateway.
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So in other words this P.C. is in Vila and 2 it's in subnet 10 1 2 0 and I'm checking that it camping
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the subnet of the device that we're trying to go to but this is the IP address of the default gateway
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into that villain.
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In other words we've proven that interval and writing is working on the layer 3 switch but now let's
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check the connectivity of PCI 2 can it get to its default gateway.
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So this is rather to acting as P.C. to show IP interface brief IP address.
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Looks right.
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Per the diagram subnet mask looks right now that information is once again not shown on the diagram.
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So we'd want to add that somewhere and you may want to add that on individual devices or make a note
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somewhere that these subnets have a slash 24 mask show IP run it shows us the default gateway of PCI
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2 so cannot ping its default gateway No it can't so there's something wrong.
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Either here or here or here let's have a look at switch for switch forwards the local access switch
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show IP interface brief it has an IP address of 10 1 1 4 can it paying such 1 in VLAN 1 yes it can show
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IP wrought default gateways tendered 1 1 2 5 4 can it paying tendered 1 dot 3 2 5 4 yes it can can it
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ping the P.C. in the violent 3 No it can't so the switch camping the default gateway into V Line routing
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is working on the default gateway but it can't ping this P.C. traffic from the switch to this piece
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you would have to traverse to here to get to the default gateway and then it would have to come back
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again let's confirm the ports on switch for so firstly show IP interface brief let's confirm that interfaces
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are up all interfaces look up including gigabit 0 1
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that interfaces up gigabit 0 0 is up which is the link to the core network pings that were previously
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so so we have an indication that this interfaces are ready up and working.
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Show interface trunk there's a trunk to the core on gigabit 0 that looks good let's have a look at the
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gigabit.
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0 1 interface show interface gigabit 0 1 switch port this interface should be in villain three.
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Can you see the problem in the this.
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Put interface.
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Name is gigabit 0.
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It's enabled as a switch port administrative mode is dynamic auto.
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It's currently acting as a static access port so dynamic trunk protocol or DTP did not negotiate to
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form a trunk so DTP is on but there wasn't a switch to negotiate drinking with noticed the problem access
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mode.
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A villain is one show run interface gigabit to 0 1 this port is not in VLAN 3.
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Interface gigabit 0 1 is currently in VLAN 1.
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So switch port access.
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Vigeland 3 show interface gigabit.
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0 1.
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Switch port Port is now an access port in VLAN 23 show run interface gigabit.
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0 1 There's a configuration.
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Let's check the local switch can ping that P.C. at the moment it still can't.
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It may take a while for spanning tree and other protocols to converge
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so you may just need to wait a bit before you assume that there's a problem but spanning tree at this
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point looks good.
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So show CTP neighbors we can see that right it to is connected to gigabit 01 using gigabit 00 show interface
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gigabit 01 switch port confirms that to this port is in V land 3 so let's go back on to the P.C. and
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check if it can ping its default gateway.
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It can now.
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So once again you may just have to wait a little bit before you assume that your change hasn't made
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any difference Kennett paying
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a one acting as P.S. 1.
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Yes it can.
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So it looks like we've solved the problem
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we could trace to the P.C. which didn't work before that now works.
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So previously when we traced to 10 1 3 2 it failed at the default gateway but now it's working and we
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could do a ping to prove it.
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And do a debug on the side to prove that the traffic arrives so that was an example of how to troubleshoot
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a local area network it can sometimes be complicated to troubleshoot a layered two issues but remember
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to check your interfaces check your v lands check your encapsulation as in other videos.
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I will show you other problems that you may encounter and need to troubleshoot in this topology open
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joint of this video.
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If he did please like it.
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Please subscribe to my YouTube channel.
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I wish you all the very best.
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