Buy or Renew
Buy or Renew
cancel
Turn on suggestions
Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.
Showing results for 
Search instead for 
Did you mean: 
cancel
Start a conversation
502
Views
0
Helpful
1
Replies

Spanning Tree Loop Troubleshooting and Safeguards ASR920-4Z-A

bass_man_123
Level 1
Level 1

‎09-26-2018 09:59 AM - edited ‎09-27-2018 08:24 AM

I have a ring of 7 ASR920's connected with trunk ports.  If I have the ring up it starts to flood and every router thinks it is the root.  So none of them are blocking. I am running spanning-tree mode rapid-pvst on all of them.  I upgraded to 16.6.1 that shows this can be configured in this mode.  Here is the some of the config of the port:

interface TenGigabitEthernet0/0/4
description link to BRNTAR_COB_City_Hall
no ip address
load-interval 30
service instance trunk 10 ethernet
encapsulation dot1q 12-18,100,102,150,800
rewrite ingress tag pop 1 symmetric
bridge-domain from-encapsulation

 

VLAN0012
Spanning tree enabled protocol rstp
Root ID Priority 32780
Address 6cb2.ae52.22bd
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32780 (priority 32768 sys-id-ext 12)
Address 6cb2.ae52.22bd
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 0 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Te0/0/4 Desg FWD 2 128.11 P2p



VLAN0013
Spanning tree enabled protocol rstp
Root ID Priority 32781
Address 6cb2.ae52.22bd
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32781 (priority 32768 sys-id-ext 13)
Address 6cb2.ae52.22bd
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 0 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Te0/0/4 Desg FWD 2 128.11 P2p

 

 

Labels:
0 Helpful
1 Reply 1

bass_man_123
Level 1
Level 1

‎09-27-2018 08:28 AM

I got the solution for the problem for Cisco tech support and it was simple.  I had the spanning-tree mode rapid-pvst in the config which tells the 920 what protocol you want to use.  You also have to turn it on the service instance trunk 10 ethernet on the interface with the following command - l2protocol peer stp so all the interfaces now look like the below config. Now spanning tree is working correctly.

 

interface TenGigabitEthernet0/0/4
description link to BRNTAR_COB_City_Hall
no ip address
load-interval 30
service instance trunk 10 ethernet
encapsulation dot1q 12-18,100,102,150,800
rewrite ingress tag pop 1 symmetric
l2protocol peer stp
bridge-domain from-encapsulation

0 Helpful
Customers Also Viewed These Support Documents