VLANs are supported with XenServer. To use VLANs with virtual machines use switch ports configured as 802.1Q VLAN trunk ports in combination with the XenServer VLAN feature to connect guest virtual network interfaces (VIFs) to specific VLANs (you can create new virtual networks with XenCenter and specify the VLLAN IDs). The XenServer management interfaces cannot be assigned to a XenServer VLAN via a trunk port - to place management traffic on a desired VLAN the switch ports need to be configured to perform 802.1Q VLAN tagging/untagging (native VLAN or as access mode ports). In this case the XenServer host is unaware of any VLAN configuration.
XenServer 6.1 removed a previous limitation which caused VM deployment delays when large numbers of VLANs were in use. This improvement enables administrators using XenServer 6.x and later to deploy hundreds of VLANs in a XenServer pool quickly.