Cannot ping after moving PC from switch to Switch

[Conwell Less]

I am trying to resolve a problem and do not know what could be wrong.

I have a 2 cisco switches that are at different sites one is a Cisco CAT4500 and other 3560. The connection between the switches is a layer 2 fibre link. CAT4500 and 3560 both have VLAN interface ip addresses in order for me to connect to the switches.

So the scenario is this:

I have PC A connected to CAT4500 and PC B connecting to 3560. All these devices are the same VLAN and in the same subnet. I do have trunk links all the way though allowing this vlan as we run vlans. From PC A, I can ping CAT4500, 3560 and even PC B. This tells me everything is fine regarding Layer 2 & 3.

The problem:

As soon as I move PC B and connect it to the other switch CAT4500 or move the other PC vice versa (this happens in both directions). Both switches learn that the mac address has moved locations and updates its mac address table accordingly. So when I do a show mac address table and show arp, everything has learned and moved fine. However when I try to ping any other device from PC B I cannot. So the 3560 switch PC B was originally connected to, I can no longer ping, the switch cannot see the pc also. It is as if PC B has not learned anything from the switch and cannot respond or reply to any icmp. I have tried this with different end devices, same thing. I am now thinking it has something to do with the switch.

Then if I leave if for let’s say an hour, then randomly it starts to work again. Where do i start troubleshooting? Is there any debug commands I can run to see what happens on Layer 2 and Layer 3 once this mac is moved or what can i try to resolve this.

All suggestions are welcome.

[InayathUlla Sharieff]

Hi Conwell,

This should typically work without any issue.

CAT4500----G4/47  connecting to G0/24 --Cat 3560

1- Vlan and the subnet mask looks good.

2- There is a trunk configured between the two looks fine.

3- Any system which are under the vlans 103 should be able to reach any pc of vlan 103 at the other end wihtout any problem.

Next Action

============

1- Kindly check if the users are assigned the correct vlan.

2- Whats the firmware running on the devices?

3- Clear the arp and as this the test environment reboot the device once.

4- Capture the outputs again.

5- Check the port status which are connectred to PC and trunk during the issue ( sh int X switchport, show spann-tree int x detail)

HTH

Regards

Inayath.

*Plz rate all usefull posts.

[Conwell Less]

Hi Sharief,

Thanks for your response.

1. Yes all the users have ip's in the same subnet in the same vlan

2. Cisco CAT 4500 running cat4500e-entservicesk9-mz.151-1.SG.bin,

    Cisco 3560 running /c3560-ipbasek9-mz.150-2.SE2.bin

3.I have tried clearing both arp and mac adress entries also rebooting.

4. Same result

5. Trunk links are setup fine, allowing vlan 103 and spanning tree also seems fine. I am using CAT4500 as root bridge for VLAN 103.

Previously we had a Cisco 3560 as well in place of the CAT and this process worked fine. Since we replaced our Core with the CAT, we experiencing this issue. The only thing i added that wasnt in place was VTP.

Also importantly, after moving the PC from switch to switch. I am unble to ping it. After a hour or so it randomly works.

I am not a expert at this but this does not make sense.

[InayathUlla Sharieff]

Hi Conwell,

Never heard of this strange issue ever. Anyway not sure if this is the feasible solution for you:

1- Can you try removing the VTP configuraiton and check the status.( though this is not the reason for the issue you are seeing but just in case.)

2- Try upgrading the cat4500 to the latest IOS.

3- Can you check with any other laptop for testing purpose which has the latest NIC drivers installed.

HTH

Regards

Inayath

[Conwell Less]

Hi,

This is a very unsual issue hence why i am so puzzled. I am going to remove VTP to check the behaviour then, i cannot do this in office hours though have to arrange a change control which i have got for tonight.

If taking off VTP does not work i will upgrade the CAT, it is part of my plan. I have tried this with laptops, servers, pc's etc. Problem still exists.

I have been researching a lot and cannot find anything concrete. I am lost for words with this situation.

Any other suggestions are welcome. Where is everyone else?

Regards,

Conwell

[Dennis Mink]

you mention that when you move the PC from one switch to another, the MAC address table gets updated with the correct path...  does this mean you checked MAC address table from end to end? so, for instance if you wnat to ping pcb (connected to the 4500) from PC A connected on the 3560, you can see the MAC address table points to the trunk port , the on the other end of that trunk port the MAC points to the access port to which PC B is connected?  Is that what you are saying?

"So the 3560 switch PC B was originally connected to, I can no longer ping, the switch cannot see the pc also", what does this mean? and how do you check?

To be honest, it does sound like some stale entry some where (CAM table), but it also seems like you checked that yourself correct?

[Conwell Less]

Hi there,

Yes i have checked this myself.

What i mean by your question is that after i moved the pc to the other switch, i run a ping and it timeouts.

Regards

[tobyarnett]

I take it that you are using DHCP on your network? I would try to use a static IP on your PC and then try and move it from switch to switch to see if the behaviour is the same. The issue may be more related to other issues such as duplicate IP's DHCP lease timers, or other issues. Check if a static IP on your machine will work.

Additionally you could check for a stale ARP/MAC entry just by removing the PC from switch A and then before reconnecting it to Switch B, you can check the ARP or CAM table to see if the entries have cleared out. They may still be there if the timer hasn't expired so you may have to wait the duration of the timer, but I would be surprised if that was your issue.

-Toby

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_____________________________________
There are no great limits to growth because there are no limits of human intelligence, imagination, and wonder.
- Ronald Reagan

[Conwell Less]

Hi there,

The machine i'm moving has a static ip assigned, i even ran a ip scanner and arp scanner to se if there is duplicate ip's. That came back fine.

The ARP/MAC entries do clear out and update after it moves so i really don't know what the problem is.

Conwell

[InayathUlla Sharieff]

Hi Conwell,

This is odd behaviour. Its time for you to consider upgrading the IOS on your switch and update us the result.

REgards

Inayath

[Conwell Less]

Hi Sharief,

Already tried that, rebooting the works.

Regards

[paul driver]

Hello

Sounds like you have exhausted a lot of possibilities.

Do you have software fws on the pcs? If so try disabling this and resetting the network interlace of the pc.

And test again

Res
Paul



Sent from Cisco Technical Support iPad App

[Conwell Less]

I have exhausted all my options yes and disabled all firewalls as well, nothing seems to solve this problem. i have tried this with access ports as well.

i am lost for words with this problem.

Regards

[tobyarnett]

Does this issue happen on the other vlans? I notice you have VLAN 114 and VLAN 124 in that same trunk. What happens if you put PC A on VLAN 114 on the 4500 and then move it to the 3560 on VLAN114, will you get the same issues as on VLAN103?

-Toby

Please don't forget to rate any helpful post.

_____________________________________
There are no great limits to growth because there are no limits of human intelligence, imagination, and wonder.
- Ronald Reagan

[Conwell Less]

Same problem Ronald, happens with all vlan's.

Regards