same subnet,different VLAN in Virtual machine

Question

I have 2 VLAN,VLAN 100 and 101 but only one subnet

i am trying to make this work with virtual machine so that VM will have two IP address in same subnet but will actually be in two VLAN.

steps followed:

created subinterface eth0.100 and eth0.101
Connected these subinterface to bridges br100 and br101
connected VNIC of VMs to these bridges

Since inside VM there is only one subnet how can i configure VM to use both VLANs.

I think the default routing table can be a problem as its not VLAN aware and the

10.0.0.0 dev eth0

above rule in ip route show can be a problem,as for all traffic in 10.0.0.0 it uses eth0 interface only,but some hosts that are in VLAN 101 may not work through eth0 with a tag of 100.

How can i make VM VLAN aware and use proper VLAN in same subnet?.

I dont have different subnets,(if i had i wouldnt have used VLAN instead use single bridge to solve this)

OR

Do i need two bridges here??

the reason i created two bridges is if i add eth0.100 and eth0.101 to same bridge,how can the VNIC of VM be connnected to proper VLAN port,since Linux bridge doesnt support tag on bridge i thought it will not work.

Can someone please correct me.

Thanks

Answer 1

It does not sound logical. If a node is trying to send a packet to an IP address that is in the same subnet as one of its IP addresses, it will send it out that interface (read: VLAN), and that is exactly what you are trying NOT to do.

You could use proxy ARP and have a host forward it to the other VLAN, but why all that extra work. Just put it into a different subnet and let the router (which is designed to do that type of forwarding) do it. The router could even firewall what it forwards!

Answer 2

Routing doesn't care about VLANs, it cares about IP networks / addresses.

Anyway: Why do you have one IP network spread across 2 VLANs? I havn't seen this up to now and it doesn't make sense to me. What do you want to achieve?