VTP Pruning and DHCP

[Alexandros Mavridis]

I have a problem i want to test the vtp pruning with trunk interfaces so i have a port with a manual pruning 

SW1#sh run int fa0/19
switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk allowed vlan 1,7,60

and the in this port i have a no cisco switch, the vlan 60 is with dhcp pool so when i have direct the vlan i port is everything ok the no cisco switch take an ip and the laptop which is in the no cisco switch connected also but when it is als trunk the no cisco SW take no ip.

So my question is how can unterstand which vlan need now ?

i am just learning so sorry if its dumb question :D 

[Giuseppe Larosa]

Hello Alexandros,

first of all VTP pruning is not related to your current configuration as you have manually configured the list of allowed Vlans on trunk.

This is different from VTP pruning because VTP pruning does not reduce the number of STP instances running (one per Vlan with PVST+ or Rapid PVST the most common STP types used in Cisco switches).

Also VTP is Cisco proprietary so you could not test it in a lab with a Cisco switch and a non Cisco switch.

Going to what you see you need to ensure that both devices agree on the native Vlan-id:

it is vlan 1 on the Cisco switch it can be a different one on the non Cisco switch for example vlan 60.

This is probably the reason why when you configure the port as a trunk carrying Vlans 1,7,60 the communication in Vlan 60 is broken.

Native vlan mismatch in 802.1Q trunk is the first aspect to check in this case.

I assume the non Cisco switch is manageable and that you can access it to check its configuration. IF it is a consumer oriented device like the ones we can buy in a supermarket they may be not able to support Vlans.

Hope to help

Giuseppe

[Alexandros Mavridis]

i have vtp pruning and is working when i have only one vlan in the interfaces but sometimes i need a trunk port thats the reason that i post this example

[Giuseppe Larosa]

Hello Alexandros,
as I tried to explain you cannot use VTP pruning to a non Cisco switch for the simple reason that VTP is a Cisco proprietary protocol and VTP ,essages are simply passed over by the non Cisco switch.

Also your configuration is that of a manual list of allowed Vlans that is not VLAN pruning.
This is good practice also between Cisco switches. I recommend it also in a Cisco only environment.
Can you provide some details on the NON Cisco switch? which vendor? it is configurable?
In this way you can get better help from the community
How do you configure the port when only one Vlan is allowed on the trunk on the Cisco side?
Do you use
switchport mode trunk
swithcport trunk allowed vlan X


Hope to help
Giuseppe

[Alexandros Mavridis]

i have this 2 tests and the vlan60 is in dhcp pool.

[Giuseppe Larosa]

Hello Alexandros,
now that I see your network drawings
I suspect the device you call Isabel is an unmanaged switch not able to support Vlan tagged traffic.
If instead Isable is configurable provide vendor and model to get better help
Hope to help
Giuseppe

[Alexandros Mavridis]

Isabel 1000Plus is the name. 

[Giuseppe Larosa]

Hello Alexandros,
OK Isabel 1000plus is the model
I did a quick search on the internet and I have found the following web page:
http://www.cbl.de/50-0-ISABEL-1000plus.html?clang=1
It is a mini switch with 4 ports to be used as access ports for PCs or IP phones one dedicated as uplink and one port to add another mini-switch in daisy chain. (TP ext I suppose)
I think most of the issue can come from the fact that Vlan 60 is defined unsecure as we can see in the GUI images you have posted. This may trigger the DHCP snooping function (if supported but datasheet is in German that I do not understand I have given a look) I would try setting the Vlan 60 as a secure Vlan first.
Then if DHCP works again you can try to find a way to declare the uplink a trusted port.

[Alexandros Mavridis]

thanks a lot i will try it

[Giuseppe Larosa]

You are wellcome,
also you can decide which Vlans is used in each port

Best Regards
Giuseppe Larosa