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Highlighted

MSTP issue. Isolation of core switch

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

6 REPLIES 6
Highlighted
Beginner

Hello,

You might want to configure VLAN 1 in MST0 to exchange bpdus

Rgds.

Highlighted

Thanks for you response.

As I know MSTP  does not send MSTI’s information in separate BPDUs, this information is  piggybacked into the IST’s BPDUs using special M-Record fields.

So,  I can have multiple MSTI or one with whole vlan range (1-4096) no  matter.

In any case, BPDU will be propagated in MST0 (Internal Spanning  Tree) and will consist of such components as configuration name,  revision number and a hash value calculated over VLANs to MSTI mapping  table contents

I think that this problem may apear due very large L2 segment. So value "Max Hops"  exhausts itself in some cases.

As a result sw-core receives BPDU 0 and after that  happens  the following scenario

sw-Core ceases to receive BPDU from all neighbors and and decides that he is root.

Upstream  switches sends superior root bridge information to the sw-Core bridge  but receives the BPDUs with Designated bit set, the upstream switch  concludes that the downstream does not hear its BPDU’s. The upstream  switch then blocks the downstream port and marks it as STP dispute link

BUT Why sw-CORE ceases to receive BPDU from ALL neighbors?  - a mystery.

Highlighted
Hall of Fame Cisco Employee

Hello Andrey,

I wonder - how many switches are connected in single ring? You also indicated that you increased "TTL" - you probably mean the STP max-hops parameter, right? What command did you use for that? Can you also confirm that none of the ports on the ring is described as a boundary port? We want to make sure that the ring is not inadvertently split into several regions.

Best regards,

Peter

Highlighted

We have eight switches in 1G ring and nine in 10G ring.

1G Ring ends on another switch not on sw-Core

You also indicated that you increased "TTL" - you probably mean the STP max-hops parameter, right?

Yes you are right. The command which we used was "spanning-tree mst max-hops"

Here Is a state of  ports

 

Gi1/1            Desg FWD 20000     128.1    P2p Edge

Gi1/2            Desg FWD 20000     128.2    P2p Edge

Gi1/3            Desg FWD 20000     128.3    P2p Edge

Gi1/4            Desg FWD 20000     128.4    P2p Edge

Gi1/5            Desg FWD 20000     128.5    P2p Edge

Gi1/6            Desg FWD 20000     128.6    P2p Edge

Gi1/7            Desg FWD 20000     128.7    P2p Edge

Gi1/8            Desg FWD 20000     128.8    P2p Edge

Gi1/9            Desg FWD 20000     128.9    P2p Edge

Gi1/10           Desg FWD 20000     128.10   P2p Edge

Gi1/11           Desg FWD 20000     128.11   P2p Edge

Gi1/12           Desg FWD 20000     128.12   P2p Edge

Gi1/13           Desg FWD 20000     128.13   P2p Edge

Gi1/14           Desg FWD 20000     128.14   P2p Edge

Gi1/15           Desg FWD 20000     128.15   P2p Edge

Gi1/16           Desg FWD 20000     128.16   P2p Edge

Gi1/17           Desg FWD 20000     128.17   P2p Edge

Gi1/18           Desg FWD 20000     128.18   P2p Edge

Gi1/21           Desg FWD 20000     128.21   P2p Edge

Gi1/22           Desg FWD 20000     128.22   P2p Edge

Gi1/23           Desg FWD 20000     128.23   P2p                  // 1G RING port

Gi1/24           Desg FWD 20000     128.24   P2p Edge

Gi1/26           Desg FWD 20000     128.26   P2p Edge

Te1/29           Desg FWD 2000      128.29   P2p                // 10G ring port

Te1/30           Root FWD 2000      128.30   P2p                 // 10G ring port

> Interface        Role Sts Cost      Prio.Nbr Type

> ---------------- ---- --- --------- --------

> --------------------------------

> Gi1/1            Desg FWD 20000     128.1    P2p Edge

> Gi1/2            Desg FWD 20000     128.2    P2p Edge

> Gi1/3            Desg FWD 20000     128.3    P2p Edge

> Gi1/4            Desg FWD 20000     128.4    P2p Edge

> Gi1/5            Desg FWD 20000     128.5    P2p Edge

> Gi1/6            Desg FWD 20000     128.6    P2p Edge

> Gi1/7            Desg FWD 20000     128.7    P2p Edge

> Gi1/8            Desg FWD 20000     128.8    P2p Edge

> Gi1/9            Desg FWD 20000     128.9    P2p Edge

> Gi1/10           Desg FWD 20000     128.10   P2p Edge

> Gi1/11           Desg FWD 20000     128.11   P2p Edge

> Gi1/12           Desg FWD 20000     128.12   P2p Edge

> Gi1/13           Desg FWD 20000     128.13   P2p Edge

> Gi1/14           Desg FWD 20000     128.14   P2p Edge

> Gi1/15           Desg FWD 20000     128.15   P2p Edge

> Gi1/16           Desg FWD 20000     128.16   P2p Edge

> Gi1/17           Desg FWD 20000     128.17   P2p Edge

> Gi1/18           Desg FWD 20000     128.18   P2p Edge

> Gi1/21           Desg FWD 20000     128.21   P2p Edge

> Gi1/22           Desg FWD 20000     128.22   P2p Edge

> Gi1/23           Desg FWD 20000     128.23   P2p

> Gi1/24           Desg FWD 20000     128.24   P2p Edge

> Gi1/26           Desg FWD 20000     128.26   P2p Edge

> Te1/29           Desg FWD 2000      128.29   P2p

> Te1/30           Root FWD 2000      128.30   P2p

Highlighted
Hall of Fame Cisco Employee

Hello Andrey,

Thank you for the additional information. Let me ask you - in the current state, does the MSTP behave correctly, or do you still experience problems? You have mentioned something related to a reboot but I did not understand what you wanted to say.

Also, please try to post the exact show command output you consider to be abnormal. I admit I am still struggling to understand what exact problems are you experiencing.

Thank you!

Best regards,

Peter

Highlighted

Hello!

I am confident that we found the problem.

The problem consisted of several mistakes

First of all, because we did not implemented the third version of the  VTP on time

And  then was an administrative mistake.  It turned out that we had  forgotten about the old switch, which was a server in the same VTP  domain as the sw-core. Despite the fact that options "no vtp"  have been  enabled, but this option works only with VTP ver. 3. So, when we had  some changes on old switch, then sw-core received higher vtp revision  and switched to client mode.  After that all neighbors worked with  sw-core on STP, because vlan database was not match for MSTP participant  and not correctly mapped to MSTI.

All for the same reason that vtp version was number 2.

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