11-14-2012 03:37 AM - edited 03-04-2019 06:08 PM
Dear All,
I have got 2 Cisco switches (3560G and a 3560X) connected by a trunk port. Please see config below:
3560G#sh run int gi0/26
Building configuration...
Current configuration : 130 bytes
interface GigabitEthernet0/26
switchport trunk encapsulation dot1q
switchport mode trunk
end
3560G#sh int trunk
Port Mode Encapsulation Status Native vlan
Gi0/26 on 802.1q trunking 1
Port Vlans allowed on trunk
Gi0/26 1-4094
Port Vlans allowed and active in management domain
Gi0/26 1,22,25,28,56,59,300
Port Vlans in spanning tree forwarding state and not pruned
Gi0/26 1,22,25,28,56,59,300
--------------------------------------------------------------------------------------
3560X#sh run int gi1/1
Building configuration...
Current configuration : 97 bytes
interface GigabitEthernet1/1
switchport trunk encapsulation dot1q
switchport mode trunk
end
3560X#sh int trunk
Port Mode Encapsulation Status Native vlan
Gi1/1 on 802.1q trunking 1
Port Vlans allowed on trunk
Gi1/1 1-4094
Port Vlans allowed and active in management domain
Gi1/1 1,25,49,79
Port Vlans in spanning tree forwarding state and not pruned
Gi1/1 1,25,49,79
--------------------------------------------------------------------------------------
I can't seem to get VLAN 79 through to the first switch (3560G). Beyond this switch there is a router with acts as default-gateway for the respective VLANs. For VLAN 79 it is 192.168.79.1. I can ping this from the first switch but can't ping it from the second (3560X) switch but can ping 192.168.25.1 which also is the default gateway for this switch.
Can someone advise what is it that i am missing in the config?
Regards,
Akbar Ali Sheikh
Solved! Go to Solution.
11-14-2012 03:43 AM
Hi,
As you can see STP not enabled on VLAN 79 on 3560G. Try to configure one access port as VLAN 79. Becase I think there is no devices on VLAN 79.
3560:
int f0/1
switchport mode access
switchport access vlan 79
And check STP on 3560G:
sh spanning-tree vlan 79
Hope it will help.
11-14-2012 03:46 AM
Hi Akbar,
Do you have any port configured with vlan 79 on switch 3560G? If not try configuring a switch port to access vlan 79 and make it up and see the result.
Regards
Najaf
11-14-2012 03:43 AM
Hi,
As you can see STP not enabled on VLAN 79 on 3560G. Try to configure one access port as VLAN 79. Becase I think there is no devices on VLAN 79.
3560:
int f0/1
switchport mode access
switchport access vlan 79
And check STP on 3560G:
sh spanning-tree vlan 79
Hope it will help.
11-14-2012 03:46 AM
Hi Akbar,
Do you have any port configured with vlan 79 on switch 3560G? If not try configuring a switch port to access vlan 79 and make it up and see the result.
Regards
Najaf
11-14-2012 05:42 AM
Hi Both,
Thank you for your help. It worked but had to create a VLAN 79 on 3560G and had to add port on it as advised.
I just got one thing to ask which is, it necessary to create a VLAN on a switch if you only want to pass the traffic through it to the onward router or switch? Does the middle switch has to have a reference to the VLAN of all passing traffic through its trunk ports.
11-14-2012 05:54 AM
As far I know yes you need a VLAN on the switch event it's just a transit to other switch. Because it's required by STP.
In order to have instance for VLAN. Logically if switch doesn't have a particular VLAN it doesn't need to particiapte in STP.
Hope it will help.
11-14-2012 07:24 AM
Manys for your prompt reply and your assistance.
11-14-2012 07:31 AM
Hi,
IMHO, STP is not the main reason.
In theory, you can run your LAN without STP.
But the switch neeeds to know where to forward the frames received.
Without the VLAN 79 configured (or received by VTP) on the switch, how could it forward frames received tagged for VLAN 79 from a trunk?
To all other trunks?
Creating a loop easily if multiple switches involved?
No, that's why the switches are building per-VLAN forwrding MAC address table.
BR,
Milan
11-14-2012 07:58 AM
Hi Milan,
Yes, you are absolutely right. Yes, because VLAN is not created it has no knowledge where to forward it. STP was just my first thought .
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