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Problem with cisco VLAN - 2960 switch

 
 
Tom
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      09-04-2012
Hello,

We have a small network (/28 mask) with two PC's and manually configured IP's.

PC's are connected to the 2960 switch on two VLAN ports to allow only two PC's at a time on this VLAN. This switch is trunked to a 1800 series router.

The problem is, if we remove a PC and try to connect another different PC with the same IP, the PC will not work unless the switch is reset.

Question - Is there a way to automate this so the switch does not have to be touched each time a new PC is connected?

Thanks.
 
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Doug McIntyre
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      09-04-2012
Tom <(E-Mail Removed)> writes:
>We have a small network (/28 mask) with two PC's and manually configured IP's.


>PC's are connected to the 2960 switch on two VLAN ports to allow only two PC's at a time on this VLAN. This switch is trunked to a 1800 series router.


Interesting odd setup.

>The problem is, if we remove a PC and try to connect another different PC with the same IP, the PC will not work unless the switch is reset.


>Question - Is there a way to automate this so the switch does not have to be touched each time a new PC is connected?


Most likely you have an ARP cache issue. In your little setup,
resetting the ARP cache timer downwards to a minute or so shouldn't
cause any issue, and then you may just have to wait a minute after you
change the IP address on a machine.

Or login to the switch and "clear arp".
 
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Tom
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      09-04-2012
On Tuesday, September 4, 2012 8:48:33 AM UTC-4, Doug McIntyre wrote:
> Tom writes:
>
> >We have a small network (/28 mask) with two PC's and manually configured IP's.

>
>
>
> >PC's are connected to the 2960 switch on two VLAN ports to allow only two PC's at a time on this VLAN. This switch is trunked to a 1800 series router.

>
>
>
> Interesting odd setup.
>
>
>
> >The problem is, if we remove a PC and try to connect another different PC with the same IP, the PC will not work unless the switch is reset.

>
>
>
> >Question - Is there a way to automate this so the switch does not have to be touched each time a new PC is connected?

>
>
>
> Most likely you have an ARP cache issue. In your little setup,
>
> resetting the ARP cache timer downwards to a minute or so shouldn't
>
> cause any issue, and then you may just have to wait a minute after you
>
> change the IP address on a machine.
>
>
>
> Or login to the switch and "clear arp".


Thanks for the quick response Doug.

Yes...this is a unique network aboard a ship at sea and resources are limited because of satellite communications.

I actually was just about to set the arp timeout and saw your response. Give me more confidence now

Seems this can be set on the router and the switch for this VLAN. I set both for now.

Thanks again!
 
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