vlan problem

Unanswered Question
Jun 7th, 2008

3 systems linked to same vlan.This vlan is present in 2 different switches. One of the systems located in the 2nd switch is unable to talk to the systems in the first switch within the same vlan.

2 systems out of this on the same switch under same vlan have no issues. But the problem is for the 3rd system to connect to the first 2 systems over the same vlan but on different switch.

Pls suggest.

Thanks in advance!!!

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mahmoodmkl Sat, 06/07/2008 - 04:48


can u confrim weather u have a trunk link between the switches.



Jason Fraioli Sat, 06/07/2008 - 04:48

Do a sh int trunk on both switches. Is the vlan in question being allowed on the trunk? Does the vlan exist in the vtp database on each switch?

foxbatreco Sat, 06/07/2008 - 05:57

yep ..it exists on the vtpdatabase.I have a smal query here.

Will similar vlans need to be allowed in the trunk if they exist on either side of the two switches?

Jon Marshall Sat, 06/07/2008 - 06:01

Your trunk should have the same set of allowed vlans on both switches.


Jon Marshall Sat, 06/07/2008 - 06:35

Okay, so

1) Vlan exists on both switches

2) Trunk link is up and allows that vlan across it.

3) Ports on both switches are allocated into same vlan.

4) You have correctly specified IP address/subnet masks on all 3 devices.

5) There is no firewalling software on any PC that could be stopping traffic.


foxbatreco Sat, 06/07/2008 - 07:01

Yes..all dese have been checked n appears to be fine.Just wondering cud there be any spanning tree issue involved here??

Jon Marshall Sat, 06/07/2008 - 08:31

Do you have multiple connections between these 2 switches then ?

If not it is unlikely to be spanning tree that is causing the issue.


sdoremus33 Sat, 06/07/2008 - 08:03

To verify this

from the switch do the following

1) Make sure you have trunking enabled over ISL or dot1q

config t


switchport trunk enable

switchport mode trunk encap isl

allow the necessary vlan to pass over the trunk

allowed vlans

This should fix the issue HTH

sdoremus33 Sat, 06/07/2008 - 08:05

Also I know you have already checked probably but is the interface associated with vlan in Layer2 mode

switchport mode access

switchport access vlan.

Just wanted to make sure

Also check to see if you are having any spanning tree issues

show spantree

Sushil Kumar Katre Sat, 06/07/2008 - 09:33


Please check if the same VLAN is configured as the native VLAN.

Check for Native VLAN mismatch.

-> Sushil

foxbatreco Sat, 06/07/2008 - 10:10

Will be checking this tommorrow.BTW how would native vlan create an issue with access??

foxbatreco Sun, 06/08/2008 - 15:56

How will the spantree status with varied port states help to identify if there is any loops occuring in the network/the vlan?


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