I am running a couple of xenserver 6.0.2 hosts with multiple vm's on them. All the xen hosts have 4 physical network ports connecting to the cisco. Each port is untagged in xen but is tagged to a vlan inside the cisco (with access mode vlan x). This is working as expected for quite some time now.

However now I would like to use one of the interfaces for multiple vlan's.

I created a new network in Xen with vlan tag 4.

The config in the cisco is (for all ports with the extra vlan in xen):

interface FastEthernet0/5
  switchport trunk encapsulation dot1q
  switchport trunk native vlan 3
  switchport trunk allowed vlan 3,4
  switchport mode trunk
  spanning-tree portfast trunk

I created 2 test vm's (on different hosts) and added the new network to them. However they cannot see (or ping) each other. I also cannot ping the cisco on its ip in vlan4.

Am i missing something? I couldn't find good documentation / tutorials online.


I make an image hoping to explain more. (http://i45.tinypic.com/33epowi.png)
VM 2 and VM 5 should be in vlan 3 (maybe untagged)
VM 3 and VM 4 should be in vlan 4
there should be no communication being possible between the vlan's
The vlan should be configured in Xen so the client cannot change it.

in my current setup, only vm 2 and 5 can communicate, 3 and 4 are isolated from everything.

  • 1
    Have you got the vlan created? What does show vlan say? – user156993 Jan 31 '13 at 16:06
  • Do you have routing enabled on the switch? – joeqwerty Jan 31 '13 at 18:33
  • @zahid it lists vlan 4 as it should. – Paul Jacobse Jan 31 '13 at 19:38
  • @joeqwerty Just found out it wasn't enabled, but got to do some research on it before i enable it. tnx – Paul Jacobse Jan 31 '13 at 19:41
  • Can you see the MAC addresses of your hosts on the switch when you run "show mac address-table" or "show mac address-table vlan 4"? – jwbensley Feb 1 '13 at 13:30

It turns out that the configuration on the cisco was correct.

On of the VM's I used for testing had a corrupted xen tools install, causing the network drivers of the internal vlan to fail. After I installed a new vm, everything worked as it should.


At the very least you'll need to enable routing on the switch unless you intend to use another router to route traffic between the VLAN's. Here's a Cisco guide to configuring InterVLAN routing on that model switch:


  • I want to keep the traffic between the different vlan seperated. without the possibility of cross-connecting. I want to give a client access to a private vlan, but i ran out of physical interfaces to use the access mode settings. Do I need to use routing for this? I though tagging was enough. – Paul Jacobse Jan 31 '13 at 20:37
  • I don't quite understand what you're asking. Hosts connected to ports in the same VLAN can communicate without a router. Hosts connected to ports in different VLAN's need a router to communicate. – joeqwerty Jan 31 '13 at 20:56

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