[c-nsp] MSTP issue. Isolation of core switch

[Andrey Teslenko]

Hello!



We have a large L2 network with one MSTI region and few ring topologies.



The topology looks like this:



Rings-*swA*-\              / ---*Ring10G* (l2 cloud)--  \

                    \         /                                       \

                     \    [Te1/29]                                  \

                    *sw-Core* [Te1/30] --- *swC*---* SW-ROOT*

                    /       \                                         /

Rings-*swB*-/            \ ----- Ring 1G (l2 cloud)--- /



It all started after the closure 10G ring.

In general periodically from all sides sw-Core sees 'BPDU received 0'.



Neighbors in the 0-th (CST) instance sees the packages, but in the 1-st
(operating) no.

After that  they put the ports into position 'blk disput'.

It is understandable, because sw-core does not see BPDU from them, so it

can not answer.

Why it does not  sees BPDU from neighbors?  - a mystery.



Increasing TTL up to 40 - have no result. Treated only reboot of switch.



IOS: cat4500-entservicesk9-mz.122-54.SG.bin





Here is configuration of MSTP



spanning-tree mode mst
spanning-tree logging
spanning-tree extend system-id
!
spanning-tree mst configuration
 instance 1 vlan 1-4094



*show spanning-tree mst*



##### MST0   vlans mapped:   none

Bridge       address 0022.55e9.f7c0 priority     32768 (32768 sysid 0)

Root         address 5057.a8ab.1380 priority     8192 (8192 sysid 0)

               port   Te1/30         path cost     0

Regional Root address 5057.a8ab.1380 priority     8192 (8192 sysid 0)

                                       internal cost 2000     rem hops 19

Operational   hello time 2 , forward delay 15, max age 20, txholdcount 6

Configured   hello time 2 , forward delay 15, max age 20, max hops   20



*show spanning-tree mst*



##### MST0   vlans mapped:   none

Bridge       address 0022.55e9.f7c0 priority     32768 (32768 sysid 0)

Root         address 5057.a8ab.1380 priority     8192 (8192 sysid 0)

               port   Te1/30         path cost     0

Regional Root address 5057.a8ab.1380 priority     8192 (8192 sysid 0)

                                       internal cost 2000     rem hops 19

Operational   hello time 2 , forward delay 15, max age 20, txholdcount 6

Configured   hello time 2 , forward delay 15, max age 20, max hops   20


============================================================

*show spanning-tree mst interface TenGigabitEthernet1/30*



TenGigabitEthernet1/30 of MST0 is root forwarding

Edge port: no             (default)       port guard : none (default)

Link type: point-to-point (auto)           bpdu filter: disable (default)

Boundary : internal                       bpdu guard : disable (default)

Bpdus sent 20, received 90131



Instance Role Sts Cost     Prio.Nbr Vlans mapped

-------- ---- --- --------- -------- -------------------------------

0       Root FWD 2000     128.30   none

1       Root FWD 2000     128.30   1-4094



============================================================

*show spanning-tree mst interface TenGigabitEthernet1/29*



TenGigabitEthernet1/29 of MST0 is designated forwarding

Edge port: no             (default)       port guard : none (default)

Link type: point-to-point (auto)           bpdu filter: disable (default)

Boundary : internal                       bpdu guard : disable (default)

Bpdus sent 89815, received 5



Instance Role Sts Cost     Prio.Nbr Vlans mapped

-------- ---- --- --------- -------- -------------------------------

0       Desg FWD 2000     128.29   none

1       Desg FWD 2000     128.29   1-4094