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MSTP Problems - Help is needed

Hi,

I'm running a full redundat layer 2 network in our datacenter with MSTP but im facing some problems and i cant find the resolution for them, so if anyone can help me i will be very apretiated.

My network topology consists in two cisco 3750 in the core/distribution layer that are running MSTP and HSRP and all switchs in the network (mixed environment with Cisco and Procurve) connects to both Cisco 3750. I will attach a picture with the network topology.

Regarding to the spanning tree i have two instances, and for instance 1 router 1 is the root and for instance2 routrr 2 is th root.

The network is working good but the big problem is when i do the show spanningtree command it apears that every switchs are ignoring the spanning tree priorities and they assume they are the root of the two instances, so every switch in the network see's himself as the root of both instances.

I dont know what i'm doing wrong, so if anyone could help me it will be great.

PS: im posting the configuration of the two core switchs/routers and one edge switch, in this case the edge switch is a Cisco 3560.

Best regards,

Nuno costa.

4 REPLIES
Hall of Fame Super Silver

Re: MSTP Problems - Help is needed

Hello Nuno,

not sure if applies to your MSTP.

Have you noticed that you have associated vlans to instance 1 and others to instance2 but also instance0 exists?

MST0

MST0
  Spanning tree enabled protocol mstp
  Root ID    Priority    0
             Address     0022.5628.f300
             This bridge is the root

is there any active vlan that is associated to instance 0?

instance0

An internal spanning tree (IST), which is the spanning tree that runs in an MST region.

Within each MST region, the MSTP maintains multiple spanning-tree instances. Instance 0 is a special instance for a region, known as the internal spanning tree (IST). All other MST instances are numbered from 1 to 4094.

The IST is the only spanning-tree instance that sends and receives BPDUs. All of the other spanning-tree instance information is contained in M-records, which are encapsulated within MSTP BPDUs. Because the MSTP BPDU carries information for all instances, the number of BPDUs that need to be processed to support multiple spanning-tree instances is significantly reduced.

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_50_se/configuration/guide/swmstp.html#wp1033176

only IST sends out its BPDUs and carries other MST instances as record fields.

So at least one vlan has to be associated to instance 0 and that vlan has to permitted on all trunk links both sides

Hope to help

Giuseppe

Re: MSTP Problems - Help is needed

Hi Guiseppe, Nuno,

Instance 0 always exists, even if there are no vlan mapped to it (it's the exception, we could not get rid of this one;-)

I saw that the two aggregation switches are in the same region at least.

However, the access switch is not part of the same region as the aggregation switches:

MST0
  Spanning tree enabled protocol mstp
  Root ID    Priority    0
             Address     0022.5628.f300
             Cost        20000
             Port        23 (GigabitEthernet1/0/23)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)
             Address     0022.5628.ff80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------

Gi1/0/23         Root FWD 20000     128.23   P2p Bound(RSTP)
Gi1/0/24         Altn BLK 20000     128.24   P2p Bound(RSTP)


So all the switches see each other (the access switch has a root port and an alternate port, it sees the agg switches), but the access switch is not in the same region as the aggs. That's why MST instance 1 and 2 don't communicate with the aggregation switches, because MST instances only work within a region.

I checked 20 times the region configuration and think it is identical (feel free to check an additional 20 times, because you never know:-) A "show mst configuration digest" may help compare.

I don't think you are hitting a pre-standard MST/standard MST interaction issue.

I recommend that you do a "clear span detected-protocol" on the access switch. If it does not help, there is I think a "debug spanning-tree mst boundary" (I'm not sure of this any more, I don't have access to a box and it's been litterally years I've not done this, shame on me!). Enable it and do the clear span detected again, that should tell you the reason why the port was put into boundary state.

HTH,

Francois

New Member

Re: MSTP Problems - Help is needed

Hi Guys,

sorry about the delay in answering this questions but i was out from the work in the last week.

Hi agree with Francois, instance 0 allways exist and in my opinion all vlans that are not mapped to any instance they are mapped to the instance 0.

Besides that a i think that the only instance that is running good is the instance 0 because in that instance all access switchs see the aggregation switchs as the root, in instance 1 and 2 they claim to be te root himselves, as you can see in this show spaning in ofne of the access switch.

Switch#show spanning-tree

MST0
  Spanning tree enabled protocol mstp
  Root ID    Priority    0
             Address     0022.5628.f300 ------------------------------------------------> this is one of the aggreg switchs so it seems to be working good the instance 0
             Cost        20000
             Port        47 (GigabitEthernet0/47)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)
             Address     0024.98bb.ba80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- ------------------------------
Gi0/3            Desg FWD 20000     128.3    P2p
Gi0/4            Desg FWD 20000     128.4    P2p
Gi0/6            Desg FWD 20000     128.6    P2p
Gi0/7            Desg FWD 20000     128.7    P2p
Gi0/8            Desg FWD 20000     128.8    P2p
Gi0/9            Desg FWD 20000     128.9    P2p
Gi0/12           Desg FWD 20000     128.12   P2p
Gi0/14           Desg FWD 20000     128.14   P2p
Gi0/15           Desg FWD 20000     128.15   P2p
Gi0/16           Desg FWD 20000     128.16   P2p
Gi0/17           Desg FWD 20000     128.17   P2p
Gi0/18           Desg FWD 20000     128.18   P2p
Gi0/19           Desg FWD 200000    128.19   P2p
Gi0/33           Desg FWD 200000    128.33   P2p
Gi0/43           Desg FWD 200000    128.43   P2p
Gi0/47           Root FWD 20000     128.47   P2p Bound(RSTP) ------> this is strange why it see's RSTP because aggre switch runs MSTP
Gi0/48           Altn BLK 20000     128.48   P2p Bound(RSTP)  ------->


MST1
  Spanning tree enabled protocol mstp
  Root ID    Priority    32769
             Address     0024.98bb.ba80   -----------------------------------------------> it claims to be the root wrongly
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0024.98bb.ba80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- ------------------------------
Gi0/16           Desg FWD 20000     128.16   P2p
Gi0/19           Desg FWD 200000    128.19   P2p
Gi0/33           Desg FWD 200000    128.33   P2p
Gi0/43           Desg FWD 200000    128.43   P2p
Gi0/47           Mstr FWD 20000     128.47   P2p Bound(RSTP)
Gi0/48           Altn BLK 20000     128.48   P2p Bound(RSTP)


MST2
  Spanning tree enabled protocol mstp
  Root ID    Priority    32770
             Address     0024.98bb.ba80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32770  (priority 32768 sys-id-ext 2)
             Address     0024.98bb.ba80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- ------------------------------
Gi0/3            Desg FWD 20000     128.3    P2p
Gi0/4            Desg FWD 20000     128.4    P2p
Gi0/6            Desg FWD 20000     128.6    P2p
Gi0/7            Desg FWD 20000     128.7    P2p
Gi0/8            Desg FWD 20000     128.8    P2p
Gi0/9            Desg FWD 20000     128.9    P2p
Gi0/12           Desg FWD 20000     128.12   P2p
Gi0/14           Desg FWD 20000     128.14   P2p
Gi0/15           Desg FWD 20000     128.15   P2p
Gi0/17           Desg FWD 20000     128.17   P2p
Gi0/18           Desg FWD 20000     128.18   P2p
Gi0/47           Mstr FWD 20000     128.47   P2p Bound(RSTP)   ---------------------> it claims to be the root wrongly,
Gi0/48           Altn BLK 20000     128.48   P2p Bound(RSTP)

Francois can you tell me how can i see if they are in the same region? they all have the same config-name and the same revison number, so they must be in the same region i guess.

Im gonna try your commands "clear span detected-protocol" and the debbuging and see what happens.

Brs,

Nuno Costa.

New Member

Hi,

Hi,

To verify your mst configuration:

#sh spanning-tree mst configuration

#sh spanning-tree mst ? ........ for more options

The mst revision number is quite important verify the value of your mst revision number using the above command.

Joel

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