Windows "Network Bridge" feature using two physical switches

[Tod Larson]

We have a Windows server 2008 server with 2 physical nics cabled to the same switch on vlan 67.  These 2 nics are bridged together using  the Windows  “Network Bridge” feature with an IP address assigned to the “Network Bridge.”  These server guys tell me this is for failover/redundancy purposes (not sure if it's the best way to achieve redundancy but that's a quesiton for another day).

This seems to work fine with only 1 physical switch.  When we cable the server to 2 switches then the we cannot get both nics to successfully join to the Network Bridge.  Our 2 switches are cabled together with a trunk that allows and sees vlan 67 through the trunk.

We actually see this issue on multiple win2003 servers and multiple 2008 servers.

Now to my questions...

Should the Windows Network Bridge feature work when cabled to two switches?

Are there any special switch configuration needed to make it work?  I think about the static arp entry needed in the router when doing windows load balancing.

Thank you.

[Reza Sharifi]

They only way you can get both NICs working is by connecting them to switches that are stacked together.  If your switches are 3750s you can stack them.

HTH

[Tod Larson]

Can you help me understand why it won't work with 2 switches trunked together?

I'm not understanding why windows blocks a bridging loop with 2 switches but doesn't with a single switch.  Perhaps a nuance of STP that I'm not seeing.

[Reza Sharifi]

So this is not about trunking. When you aggregate multiple physical links, the physical devices need to have a way to see if one link goes down use the other one. So the only way to accomplish this is by stacking the switches together.  When you stack lets say 5 switches together, they logically become one switch.  Now you can have a server with for example 5 NICs and connect each NIC to a different switch using Etherchannel and this will work fine. Or if you are using 6500 series you can do the same with VSS which also makes multiple chassis (max 2) to look as one switch.

Hope it is more clear.

HTH