[Users] VLANs and oVirt 3.1

In my test setup for oVirt 3.1, I have 3 switches -- two basic ones with no VLAN support for mgmt, and storage, and a building switch with VLAN support. The network operations team has configured a trunk with 2 dual 1 Gb links on the building switch. If I configure the two network interfaces in oVirt with binding mode 4, and assign a logical network to the link without specifying a VLAN, it works fine. I'm told the default untagged VLAN is 494 (which is what I want). On the other hand, if I simply hard-code VLAN 494 in the logical network setup, it doesn't work - I get no network traffic. I'm told that the switch is setup correctly, and the problem is on my side. How can I debug? Thanks, Jason.