ISR4000 series with switch module - no spanning tree instances exist

[Alex Willoughby]

Good morning, 

We have the 24 port switch modules running inside our ISR 4331s (SM-X-ES3-24-P).

Vlans are created on the router and the router trunks via the Ethernet-Internal1/0/0 interfaces to the module.

However we cannot see any spanning tree information on the router. the router accepts spanning tree commands but 

LAB-RTR-01#sh run | i span
spanning-tree extend system-id
spanning-tree vlan 1,5,10,15 priority 0

but cannot view anything

LAB-RTR-01#show spanning-tree

No spanning tree instance exists.

LAB-RTR-01#show spanning-tree vlan 5

Spanning tree instance(s) for vlan 5 does not exist.

We are running 16.6.3 on the ISR, does anyone know if there are any additional commands required to view this information or if its missing perhaps?

Thanks

[a.alekseev]

#hw w session 1/0
https://www.cisco.com/c/en/us/td/docs/routers/access/interfaces/eesm/software/configuration/guide/4451_config.html

[Alex Willoughby]

Hi, thanks for the input, but we were already aware of how to console into the switch. 

The issues are with the router not showing any spanning tree info.The switch module has all the spanning tree info, which is great, but the router holds the SVIs and we are unable to view any spanning tree info from the router

[a.alekseev]

Show the configuration of the switch.
Have you configured spanning tree on the switch?
Show the output from the switch
"Sh spanning-tree"

[Alex Willoughby]

yes the switch is fully configured and working as expected

from the switch

STR-LAB-01-SW-01#sh spanning-tree

VLAN0001
  Spanning tree enabled protocol rstp
  Root ID    Priority    32769
             Address     0041.d2b4.7780
             Cost        4
             Port        24 (GigabitEthernet0/24)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     046c.9db3.df00
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/24              Root FWD 4         128.24   P2p Peer(STP)
Gi0/26              Desg FWD 4         128.26   P2p

from the router, the router should be the spanning tree root bridge with priority set to 0 but it doesnt seem to be participating at all, in spite of it accepting spanning tree commands

STR-LAB-01-RTR-01#sh spanning-tree

No spanning tree instance exists.

STR-LAB-01-RTR-01#sh run | i span
spanning-tree extend system-id
spanning-tree vlan 1,5,10,15,20 priority 0
STR-LAB-01-RTR-01#sh vlan

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active
5    DATA                             active
10   VOICE                            active
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1    enet  100001     1500  -      -      -        -    -        0      0
5    enet  100005     1500  -      -      -        -    -        0      0
10   enet  100010     1500  -      -      -        -    -        0      0
1002 fddi  101002     1500  -      -      -        -    -        0      0
1003 tr    101003     1500  -      -      -        -    -        0      0
1004 fdnet 101004     1500  -      -      -        ieee -        0      0
1005 trnet 101005     1500  -      -      -        ibm  -        0      0

Primary Secondary Type              Ports
------- --------- ----------------- ------------------------------------------

STR-LAB-01-RTR-01#

[a.alekseev]

The router cannot be the spanning tree root bridge for the switch.

[Alex Willoughby]

is this documented anywhere? must the switch be the root instead? Which doesn't make much sense, the SVIs are on the router, the VLANs exist on the router, HSRP is on the router. The switch modules themselves are seen as a separate device.  Surely the router should be the root?

[a.alekseev]

Think about the module as a l3 switch.
If you need some advanced features (nat, firewall etc) which switch cannot do by itself you can put l3 interfaces from the router into the switch.

I cannot find right docs, but in any case you can open the case with Cisco TAC and ask them for clarification.