[c-nsp] Spanning tree issues

[Matthew Crocker]

I'm sure I'm being stupid here but I can't figure out what is going on.

I have 2 switches connected together via 2 GigE links,  they are not  
bonded (no EtherChannel).  I want link one to act as a backup to the  
other link.  I don't care which link is primary

one switch is a 3550-12G the other is a Paradyne IPD12000E 'dslam'.   
When I connect both GigE links the traffic starts looping and in about  
30-40 seconds the 3550 melts and I lose console access/response.   
yanking either of the links restores everything instantly.    I'm sure  
it is a spanning tree problem but isn't looping exactly what it is  
supposed to detect and protect against?

The 3550-12G should always be the spanning tree route.

Topology is

7206 ---- 3550-12G ==== Paradyne IPD12000E ----- Paradyne IPD12000E

-----  = single GigE
===  = dual GigE

The IPD12000 supports EAPS,  wish the 3550 did :/

c3550-12G-1#show version
Cisco IOS Software, C3550 Software (C3550-IPSERVICES-M), Version  
12.2(25)SEB2, RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2005 by Cisco Systems, Inc.
Compiled Tue 07-Jun-05 22:16 by yenanh

ROM: Bootstrap program is C3550 boot loader

  c3550-12G-1 uptime is 3 years, 6 days, 5 hours, 44 minutes
System returned to ROM by power-on
System image file is "flash:c3550-ipservices-mz.122-25.SEB2/c3550- 
ipservices-mz.122-25.SEB2.bin"

Cisco WS-C3550-12G (PowerPC) processor (revision N0) with 65526K/8192K  
bytes of memory.
Processor board ID CAT0916X0XE
Last reset from warm-reset
Running Layer2/3 Switching Image

The 3550 is being used for L2 only,  L3 is handled by a 7206 NPE-G1

Here is my config:

spanning-tree mode rapid-pvst
spanning-tree loopguard default
spanning-tree logging
spanning-tree extend system-id
spanning-tree vlan 1-2000 priority 24576
!
interface GigabitEthernet0/4
  description Link to NATNMAMA via West route
  switchport trunk encapsulation dot1q
  switchport mode trunk
  flowcontrol send off
  mls qos trust dscp
  auto qos voip trust
  wrr-queue bandwidth 10 20 70 1
  wrr-queue queue-limit 50 25 15 10
  wrr-queue cos-map 1 0 1
  wrr-queue cos-map 2 2 4
  wrr-queue cos-map 3 3 6 7
  wrr-queue cos-map 4 5
  priority-queue out
  random-detect dscp-based
!
interface GigabitEthernet0/10
  description Link to NATNMAMA via East route
  switchport trunk encapsulation dot1q
  switchport mode trunk
  flowcontrol send off
  mls qos trust dscp
  auto qos voip trust
  wrr-queue bandwidth 10 20 70 1
  wrr-queue queue-limit 50 25 15 10
  wrr-queue cos-map 1 0 1
  wrr-queue cos-map 2 2 4
  wrr-queue cos-map 3 3 6 7
  wrr-queue cos-map 4 5
  priority-queue out
  random-detect dscp-based