[c-nsp] MACFLAP loop with l2pt

[Erik Klaassen]

Hello,

I have created a l2pt between sw1-gi0/1 and sw2-gi0/1 so both switches are logical connected.
The te1/1 interface has the lowest cost so gi0/1 in sw2 goes in BLK state.
When the connection between sw4 and the isp swich goes down, the link between sw2 and sw4 stays up but no bpdu's are received.
gi0/1 in sw then goes in FWD state. So when the link between sw4 and isp comes up you have loop till some bpdu is received on sw2 gi0/1. 

How can i prevent this interface going in fwd state? What am i missing?

Kind regards
Erik



                     gi0/1 do1q      gi0/1 access vlan 170
                     vlan23          mode dot1q-tun, l2pt stp
      +-----------------+              +-----------+
      |  sw1 root br    +--------------> sw3       |
      |                 |              |           |
      +-+---------------+              +-----+-----+
        | te1/1 vlan 23                      |
        |                                    |
        |                                    |  trunk dot1q vlan 170
        |                                    |
        |                           +--------v---------+
        |                           |   isp l2 network |    non cisco
        |                           +--------^---------+
        |                                    |
        |                                    |
        |                                    |
        |                                    | trunk dot1q vlan 170
        |                                    |
        |te1/1 vlan23                        |
      +-v----------------+            +------+----+
      | sw2              |X           |sw4        |
      |                  +------------>           |
      +------------------+            +-----------+
                   gi0/1 dot1q       gi0/1 access vlan 170
                   vlan 23           mode dot1q-tun, l2pt stp