Having a strange issue with STP that I cannot seem to pin down with the following topology:
-------881 ------- Public WAN ----- 881--- Switch1 Swith2 --------2911--------Private leased line---- provided by isp
I am trying to extend a layer 2 network between two remote sites, the two bottom routers are cisco 2911's connected through a leased line from the ISP. The two routers at the top are cisco 881's connected over an encrypted VPN tunnel over public WAN. The 881 link is supposed to serve as a backup link to the link between 2911s.
Using pesudowire I have set up the network such that STP packets can freely flow between the switched, simulating a LAN. I can see BPDUs being sent and received in appropriate locations however there seems to be a problem with failing over to the secondary link when the primary goes down in a certain way.
Operating normally the non-root switch (on the right) blocks its link to the 881, getting rid of the loop. When the link between the switch and the 2911 is broken STP unblocks the port and traffic between the two sites flows normally.
However, when the link between the two 2911's is broken STP cannot seem to switch over to the other link and traffic stops transmitting between the 2 sites.
Think there might be something about the STP configuration since traffic seems to be flowing as expected until a failure but I can't be sure anymore. Any ideas with something similar would be great.