Question Regarding VoIP using two VLANs within the same subnet

[ccctech]

I am about to try to link two IP500V2 systems together with VoIP Phones across a MPLS circuit, I know this is a Definity/Communication Forum, but the concept using 9620 phones would be the same.
Site 1:
Data VLAN 1 for PC's using 10.1.1.x network and Voice VLAN100 using 10.1.100.x with both using subnet 255.255.0.0 and default gateway 10.1.1.1

Site 2:
Data VLAN 1 for PC's using 10.2.1.x network and Voice VLAN100 using 10.2.100.x with both using subnet 255.255.0.0 and default gateway 10.2.1.1

My question is; I realize each location has its own network domain, but each location's voice and data traffic is technically using the same broadcast domain, however the VoIP traffic will be on a separate VLAN will there be any voice quality issues? I have only set this scenario up before when both data and voice vlan's are on the different subnets and default gateways and works great. Also if this is acceptable, would the Ethernet Switch port connected to the router be setup as a Trunk to carry both VLAN 1 and 100 even though both VLAN's devices are using the same default gateway?

Thank you in advance for any guidance.

 

[TDMorIP]

If QoS in turned on all the way through then latency shouldnt be a problem. But by having the 2 different VLANs on the same subnet isnt really helping anything at all, in fact i think the router could potentally see some issues having them bonded like that. i have never tried doing that. why not create 2 new subnets per site and seperate the broadcast traffic limiting your exposure for voice problems.

 

[zeropoint46]

If you're worried about the fact that you have VLAN100 and VLAN1 defined in both locations. It wont be an issue. Vlans are at layer 2 of the OSI model, once you route those packets through your mpls link you've moved now up to layer 3. You will not have any VLAN conflicts unless site a and site b are connected at a layer 2 level with some kind of l2tunnel. Explicitly stated, a broadcast layer 2 message from VLAN1 at site A will not travel to Site b over the mpls, if this were happening you'd see an issue or evidence already. Since you have 2 separate subnets you'll be fine. I would just echo what TDMorIP has said, make sure you have QoS and you're using a nicely compress codec like g729. In short VLAN1 from site A doesn't know about VLAN1 in site B and same with VLAN100.