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Switch trunk ports

Posted on 2010-11-10
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Last Modified: 2012-06-21
I have a couple of Cisco 3750's in a cross stack configuration.  I have a couple of VLAN on these switches.  Most ports are going to storage in a LACP config.  I have older Foundry 4802-POE's that run to the IP phones and the client machines connect through the back of the IP phones.

What I want to do is connect 2 ports (g1/0/12, g2/0/12) to the gig uplink port on two of the 4802's.  The uplink I want to share with VLAN 16 on the CISCO side.  That way if I lose one 3750, I still have access.

From a L2 perspective, how do I do this?  

Thanks,
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Question by:banditti
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Otto_N earned 500 total points
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I'm not sure that I understand your question correctly, so let me know if I'm answering a question you did not ask.

To do this physically, you would just connect the cables, and ensure that the ports are configured as trunk ports.  This is if I assume that you need all the VLANs on the 3750 stack available on the Foundry switches.  If you want to limit the VLANs caried on the trunk links (i.e. only allow VLAN 1 to 5 and 16), you can configure this using the "allowed vlan" command.  So a config will look like this (on the Cisco switches):

interface gig1/0/12
 switchport trunk allowed vlan 1-5,16
 switchport trunk encapsulation dot1q
 switchport mode trunk

If you only want to allow a single vlan (such as vlan 16) rather configure the port as an access port in vlan 16:

interface gig1/0/12
 switchport mode access
 switchport access vlan 16

You also repeat this configuration on the other uplink port (gi2/0/12).  Spanning Tree Protocol (STP) should be enabled by default on all your switches, and will take care of the Layer2 loop by blocking one of the interfaces.

Take note that the config above is for the Cisco switches.  Let me know if I need to get the Foundry configurations for you as well.
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