On my company's network, we have small branches on the same block. To avoid the cost of ISP or WAN links, we use wireless bridges pairs to interconnect them, extending vlans with trunk interfaces.
Unfortunately, due to our small budget, we cannot use layer3 connections. Using layer 2 our alternatives to high availability were etherchannel or spanning-tree.
We weren't able to use etherchannels because of its issues related to the management interface of the bridges - under the etherchannel they became inaccessible due to the behavior that is common to the logical interfaces of a channel.
So... after this sad explanation... spanning-tree was the only option... :(
We decide to use port-priority to control the default behavior of our links. By default, we choose one pair of bridges to some vlans, while to another group of vlans the other pair assumes. And the configuration is kept on the main building, instead of manipulate cost on the remote branch.
I had struggled to understand why this wasn't working. The port-priority configuration wasn't working as desired. To keep high-availability, we use our switches on stack-ring with one wireless bridge on the first switch and the other bridge on the second switch. I realized that when I put both redundant interfaces on the same switch of the stack, the port-priority works as expected.
So, after search on the internet, I've found CSCea40988 bug. And it seems that it's behavior still occurs. Our devices are WS-C3750X, with IOS 15.0(1)SE3.
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