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VLAN trunking

I have 3 switches connected in daisy chain: switch1---switch2---switch3
All switches configred with open trunk.

If I want to trunk a vlan 10 from switch 1 down to switch 3, is it necessary
to create vlan 10 locally on switch 2?

My understanding is if it is an open trunk, all VLANs will allow through that trunk. I came across this problem where I have to create a vlan 10 locally on switch 2 before switch 3 can see vlan 10, although all switches have open trunk.

Any ideas?

3 REPLIES
Cisco Employee

Re: VLAN trunking

after1111 wrote:

I have 3 switches connected in daisy chain: switch1---switch2---switch3
All switches configred with open trunk.

If I want to trunk a vlan 10 from switch 1 down to switch 3, is it necessary
to create vlan 10 locally on switch 2?

My understanding is if it is an open trunk, all VLANs will allow through that trunk. I came across this problem where I have to create a vlan 10 locally on switch 2 before switch 3 can see vlan 10, although all switches have open trunk.

Any ideas?

Unless you configure a VLAN on a particular switch (either explicitly or automatically by switch when a port is assigned to a VLAN) the Layer-2 switching functionality for that VLAN is not turned on and unless this functionality is not turned on you will not be able to pass traffic for that VLAN across the switch. Configuring a trunk is one thing but the VLANs being carried on the trunk need to exist in the VLAN database as well. In short the VLAN in question should be visible in the output of the 'show vlan id ' command.

Atif

Purple

Re: VLAN trunking

  Depends if you are running transparent mode or client/server .  If running client/server the vlan would just need to be created on the server and it would get propagated to all the clients , if in transparent mode then yes you do have to create the vlans across all switches in the path itself  from SW1 to Sw3 .

Hall of Fame Super Blue

Re: VLAN trunking

Just to add to the others -

I was involved recently in a thread where someone was using the Cisco emulator (name escapes me !) to test this very thing. With the emulator you didn't need to add the vlan on the itntermediate switch but from my experience i agree with Atif when he says with real switches the vlan must exist in the vlan database on the switch for that switch to pass traffic.

By the way, you have posted quite a few questions which people have been only too happy to help with. No problem with this as that is what NetPro is for but if your anwers are resolved could you please consider rating posts, it helps others find correct answers and shows appreciation for the people who help out.

Jon

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