Spanning-Tree MST

Hi,
we have the following configuration on our switches
spanning-tree mode mst
spanning-tree extend system-id
spanning-tree mst configuration
name test
spanning-tree mst forward-time 4
when we have a failover convergence time was about 8-10 seconds outage is there anything on the above config that suggest's this could be causing the delay? i thought MST was fast convergence times?
Thanks

i will try and you this later on. Not sure it was already in place what are the difference's between them both i thought MST can have multiple vlans per region so better design. Is RSTP not the same as PVST? not done much spanning tree as of yet. so not had chance to look at the differences?
Thanks

Similar Messages

Spanning Tree MST per Vlan, best practice

Hi Community.
I did the following MST Spanning Tree Config
spanning-tree mst configuration
name xxxxxxx
revision1
instance 1 vlan 1, 10-20, 25, 30
So I added every Vlan to the config which we use. But every time when I add one more vlan to the config the whole network get a little outage.
I see lots of MAC Flaps on ports with two Server links and the outage is for some seconds.
Is it a better practice to add all possible Vlans to the config. So I do the config like that:
instance 1 vlan 1-4096
What you think.
Best Regards patrick

Hi,
So I added every Vlan to the config which we use. But every time when I add one more vlan to the config the whole network get a little outage.
Correct, that is normal behavior with MST.
I would just add "instance 1 vlan 1-4094" this way there is no outage when you bring up a new vlan.
HTH

Why does the command "spanning-tree mst simulate pvst disable" exist

That's all really. Why would you turn it off? What is the advantage. If you're not receiving PVST BPDUs, you don't need it, but why turn it off?

When you use the spanning-tree mst simulate pvst disable command, specified MST interfaces that receive a Rapid PVST+ (SSTP) bridge protocol data unit (BPDU) move into the STP blocking state. Those interfaces remain in the inconsistent state until the port stops receiving Rapid PVST+ BPDUs, and then the port resumes the normal STP transition process.
OK, that's what it does, but why? the only effect it has is blocking your ports.

What is the command to check the changes in the spanning-tree topology?

What is the command to check the changes in the spanning-tree topology?

Hi,
Few commands which would help are:
1- Show spanning-tree detail
2-show spanning-tree detail | in ieee|from|occur|is exec >> This will give from were the changes occuring- Ex:
C6K1#show spanning-tree detail | in ieee|from|occur|is exec
VLAN0001 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 9536 last change occurred 00:00:29 ago
from GigabitEthernet4/6
3- show spanning-tree active *& show spanning-tree root >> Will give you the root information.
4- show spanning-tree inconsistentports >> If there are any port which are inconsistent state due to STP features.
STP running MST:
===============
show spanning-tree mst configuration >> Need to check and match the same outputs with the other switches running in the same MST domain/region.
show spanning-tree mst detail
show spanning-tree mst <name of the region>
Debug on STP:
============
debug spanning-tree events/bpdu >> would be good but to be run with more cautious.
HTH
Inayath
*Plz rate if this info is usefull.

Spanning tree for VLANS

Hi,
I need an answer to this puzzling scenerio i have been asked to work with.I have two vlans with about 10 switches on each end and there is a link switch that has a connection to both sides of the VLAN. I have been asked to create a singular spanning tree for the entire scenerio. how can i go about this.
please i am awaiting the opinions of anyone knowledgable in this line. thanks.

Hi, I agree you can config MST on your router to reduce the number of spanning tree instances runing on the switch from one per vlan. You will have to map your vlan range to the MST, useful CLI commands are
spanning-tree mode mst
spanning-tree mst configuration
name (name)
revision( revision number)
instance (number) vlan (vlan range)
check your config using
show spanning-tree mst configuration.
Hope thsi will hlep you get started.
DW

Spaning Tree MST P2p Dispute

hi
i have a pair of C3750X running IOS 15.2(1)E
they are connected over througt a WAN (Layer2 VPLS 802.1Q) connection.
the port on the Root Bridge is in a block state because there is a P2p Dispute. anyone got a clue to why this i happening
below is the port configuration, spanning tree configuration i have attached debug output from the Root Switch
Root Switch
spanning-tree mode mst
spanning-tree logging
spanning-tree extend system-id
spanning-tree mst 0 priority 4096
interface GigabitEthernet1/0/1
description ** xxxxxxx **
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 276-281
switchport mode trunk
storm-control broadcast level 2.00
2nd switch
spanning-tree mode mst
spanning-tree logging
spanning-tree extend system-id
spanning-tree mst 0 priority 28672
interface GigabitEthernet1/0/1
description ** xxxxx **
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 276-281
switchport mode trunk

Hi,
The problem can be caused by STP or EtherChannel misconfiguration, or by an uni-directional link.
1- You can check the bi-directional functionality of the link or MST configuration?
2- if you configured "vlan dot1q tag native" , remove it.
Houtan

Mono spanning-tree and PVST

Refering to these two links
http://www.cisco.com/en/US/tech/tk389/tk390/technologies_tech_note09186a0080094665.shtml
http://www.experts-exchange.com/Hardware/Routers/Q_21349385.html
IEEE 802.1Q defines a single instance of spanning tree running on the native VLAN for all the VLANs in the network which is called Mono Spanning Tree (MST). This lacks the flexibility and load balancing capability of PVST available with ISL. However, PVST+ offers the capability to retain multiple Spanning Tree topologies with 802.1Q trunking.
IEEE 802.1Q defines a single instance of spanning tree running on the native VLAN for all the VLANs in the network which is called Mono Spanning Tree (MST). This lacks the flexibility and load balancing capability of PVST available with ISL. However, PVST+ offers the capability to retain multiple Spanning Tree topologies with 802.1Q trunking.
http://networking.ringofsaturn.com/Certifications/BCMSN.php
Per-VLAN Spanning Tree (PVST) ? A Cisco proprietary method of connecting through 802.1Q VLAN trunks, the switches maintain one instance of the spanning tree for each VLAN allowed on the trunk, versus non-Cisco 802.1Q switches which maintain one instance for ALL VLANs. This is the default STP used on ISL trunks.
http://www.informit.com/content/images/1587051427/samplechapter/1587051427content.pdf
The 802.1Q standard defines one unique Spanning Tree instance to be used by all VLANs in the network. STP runs on the Native VLAN so that it can communicate with both 802.1Q and non-802.1Q compatible switches. This single instance of STP is often referred to as 802.1Q Mono Spanning Tree or Common Spanning Tree (CST). A single spanning tree
lacks flexibility in how the links are used in the network topology. Cisco implements a protocol known as Per-VLAN Spanning Tree Plus (PVST+) that is compatible with 802.1Q CST but allows a separate spanning tree to be constructed for each VLAN. There is only one active path for each spanning tree; however, in a Cisco network, the active path can be
I could not get exactly what these Terminology (PVST, instance, PVST+, MST, etc) trying to achieve ?
Any URL and online resource help me to do some extar reading to clarify these terminology

Hi,
The URLs that you have provided all explains the same technical details in different fashion.
I will summarise them here for better clarity.
There are two separate technologies that needs clarity.
1) Method of Trunking many vlans across a link
2) Spanning tree
Now for point 1, we have the IEEE standard 802.1q, which mentions how multiple vlans can be carried across a link. As per this standard a 4 byte tag will be inserted in the ethernet packet, ( inserted between the Destination mac address field and the ethertype field)
This tag will contain the vlan identifier info and some other details ( available in the urls that you have highlighted)
Cisco has a proprietary technology called ISL which effectively does the same job in a different fashion but can only be used in cisco devices.
Now for point 2, again we have IEEE standards like 802.1d ( common/mono spanning tree), 802.1w/RSTP ( Rapid spanning tree) and 802.1s/MSTP.
In 802.1d, there will be only one spanning tree process/instance running for the whole network, irrespective of how many vlans are involved in the network. Hence the whole network is treated as one common domain by the STP protocol.
So, there can be only one root bridge in the network and other bridges will intelligently block the redundant links, we wont have much control to effectively utilise the redundant links.
IEEE 802.1w/RSTP also works in the same fashion, but the convergence time is very fast in this protocol.
Here also there is only one spanning tree instance involved.
In both the above STP protocols, there is only one instance/process of the protocol running in the network, which is common for all vlans. Hence these protocols consume only very less CPU utilisation.
In 802.1s/ MSTP ( multiple spanning tree), extends the 802.1w Rapid Spanning Tree Protocol (RSTP) to have multiple STP instances. In this protocol, we can group the desired vlans in to one Instance of the protocol.
Say for example, lets assume a typical campus network with multiple access switches, 2 distribution/core switches.
Access switches having dual connectivity to the distribution/core switches.
In this topology if we deploy 802.1d or 802.1w, the redundant links from the access switches to the distribution/core switches will be blocked. Only one uplink from the access switch to the distribution layer will be working at any point.
In this network, only one distribution/core switch will be root bridge for the entire network.
But if we deploy 802.1s for this network, we can design it as follows.
We can split the vlans in to two groups,
Group1 => vlan 1 to 50
Group2 => vlan 51 to 100
We can create two instance of MSTP protocol with the following mappings
Instance 1 => for Group 1, with one distribution/core switch as the root bridge
Instance 2 => for Group 2, with another distribution switch as the root bridge
--Continued

Can I disable spanning-tree in a vpc domain ?

i have two N7718s in a vpc domain and each have a vpc connection to 300+ TORs(non cisco switch).
each 7718 have 300+ trunk port and a trunk port carring 80 vlans . so the logical port number is 300*80 = 24000
the problem is n7k r-pvst logical ports limit is 16000,it causes the vpc primary 7718 ping latancy time exceed 1000ms
2 ways to solve this problem : use mst instead of rpvst or disable spanning-tree
if i use mst , the logical ports limit is 90000, the problem will appear one day
so i want to disable spanning-tree . 7718s' vpc link to TOR use lacp ,it will prevent some layer2 loops. can i do it?

I have the same problem. :)

Spanning-tree link-type shared

Hi,
i 've this problem.
My PC must boot OS (windows) from network (Server sends Operating System by PC's mac-address)
PC needs a ip-address within 5-10 seconds.
I try it using hub and PC loads correctly OS and works properly.
I try on my network (without hub) using Catalyst Switch in 2 ways:
IOS and CatOS
For the IOS i find this solution:
i use the follows CLI:
spanning-tree portfast
spanning-tree link-type shared
in this case i resolved my problem.
FOR catOS , this command not work properly
i use the follows CLI:
set spantree portfast mod/port enable
set spantree link-type mod/port shared
After, if i see the configuration , i find the CLI
"set spantree mst link-type mod/port shared"
Can you help me?
Thanks
FCostalunga

Configuring a ports STP link type to shared is sort of invalid if the port is also configured as an STP portfast port. 'Shared' effectively means this is a half-duplex connection to a hub that may also be connected to another switch (hence it can't be a point-to-point link). Normal STP operation should operate over 'shared' links and you won't get the rapid start a P2P link has.
If the port is connected directly to a host then simply configuring the port as a portfast port will be enough (it will also make it a P2P link by default).
HTH
Andy

SF 300 Serires switch not participating in spanning tree?

I just purchased an SF300-24 managed switch and I am running it in layer3 mode. I am testing it out right now and have it connected to two 2950 switches. The SF300 is connected to each 2950 with a four port etherchannel running LACP. When looking at spanning tree all three switches are configured the same when it comes to hello, forward, max age and all three are in RSTP mode. I adjusted the priorities so that the SF300 would be the root but that is not happening.
I only have one VLAN as of right now set up and connectivity between the three switches is fine. The only problem seems to be that the two 2950 switches are the only two switches involved in the determination of the root bridge. Additionally it was the same way before I configured the etherchannel and had the switches connected over single trunk lines.
I would appreciate if someone can expain to me why this is?
Thanks in advance.

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Thanks for your help but know I still cannot get the three devices to talk MST either,it is getting frustrating. If i add a redundant link and directly connect the two 2950's they immediately talk and configure MST. But when I remove that link no info is passed and both 2950's think they are the root even though the SF 300 priority is 0 on all three MST instances. On the SF300 I have the following settings:
Spanning tree: enabled
STP Operation Mode: Multiple STP
BPDU Handling: Flooding
Path Cost: Long
Region name: test
Revision: 1
Max Hops: 20
Max-age: 20
Hello Time: 2
Forward Delay: 15
MST instance 1 Vlan 100
Bridge Priority 0
Designated Root Bridge: Self
Root port: 0
Root path cost: 0
MST instance 2 Vlan 2-5
Bridge Priority 0
Designated Root Bridge: Self
Root port: 0
Root path cost: 0
MST instance 0 all vlans not in instance 1 and 2
Bridge Priority 0
Designated Root Bridge: Self
Root port: 0
Root path cost: 0
For MST interface Settings (both LAGs/instances are thesame)
Int Priority: 128
Path Cost: 20000
Port State: Boundary
Mode: RSTP
Type: Boundary
Designated port ID: 128
Designated Cost: 0
Remain Hops: 20
Forward Transitions: 1
The 2950 switches: (The only difference on the other switch is that the priority is 8192, and the MACs of course)
MST00 is executing the mstp compatible Spanning Treeprotocol
Bridge Identifierhas priority 4096, sysid 0, address 000b.460e.e040
Configured hello time 2, max age 20, forward delay 15
Current root haspriority 0, address 6c50.4dcb.334b
Root port is 65 (Port-channel1), cost of root path is 50000
Topology change flag not set, detected flag not set
Number of topology changes 7 last change occurred 00:18:54 ago
          from Port-channel1
Times: hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0
Port 65 (Port-channel1) of MST00 is root forwarding
   Port path cost 50000, Port priority 128, Port Identifier 128.65.
   Designated roothas priority 0, address 6c50.4dcb.334b
   Designatedbridge has priority 0, address 6c50.4dcb.334b
   Designated port id is 128.1000, designated path cost 0
   Timers: message age 4, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type ispoint-to-point by default, Boundary RSTP
   BPDU: sent 571,received 568
MST01 is executingthe mstp compatible Spanning Tree protocol
Bridge Identifierhas priority 4096, sysid 1, address 000b.460e.e040
Configured hello time 2, max age 20, forward delay 15
We are the root of the spanning tree
Topology change flag not set, detected flag not set
Number of topology changes 9 last change occurred 00:18:55 ago
          from Port-channel1
Times: hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0
Port 65 (Port-channel1) of MST01 is boundary forwarding
   Port path cost 50000, Port priority 128, Port Identifier 128.65.
   Designated root has priority 4097, address 000b.460e.e040
   Designated bridge has priority 4097, address 000b.460e.e040
   Designated port id is 128.65, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type ispoint-to-point by default, Boundary RSTP
   BPDU: sent 598,received 0
MST02 is executingthe mstp compatible Spanning Tree protocol
Bridge Identifierhas priority 4096, sysid 2, address 000b.460e.e040
Configured hello time 2, max age 20, forward delay 15
We are the root of the spanning tree
Topology change flag not set, detected flag not set
Number of topology changes 9 last change occurred 00:19:50 ago
          from Port-channel1
Times: hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0
Port 65 (Port-channel1) of MST02 is boundary forwarding
   Port path cost 50000, Port priority 128, Port Identifier 128.65.
   Designated root has priority 4098, address 000b.460e.e040
   Designated bridge has priority 4098, address 000b.460e.e040
   Designated port id is 128.65, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type ispoint-to-point by default, Boundary RSTP
   BPDU: sent 611,received 0
I notice that on MST01 and 02 they are not receiving BPDU’s,but I am not sure why or if that is the problem. It appears that the SF 300 is not sending BPDU packets for MST01 and 02, but is sending them for MST00. I also attached a capture. I captured the VLAN info for VLAN 100 which is in MST1. on the SF300, it appears that the SF 300 is recieving STP traffic but not generating any.

Different spanning tree modes in 1 network

I've noticed that we use MST and PVST in our network, is this a good way to tackle spanning tree ? ( I guess not ) and how am I able to disable MST and use PVST instead.
Also, what impact will it have if I change MST to PVST ?

MST allows you to build multiple spanning trees over trunks. You can group and associate VLANs to spanning tree instances. MST converges faster than PVST.Refer the following URL for more information
http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_guide_chapter09186a008007e71a.html#wp1050594

Change of spanning-tree root

Hi,
Would appreciate some advise on the following:
The network has already been configured with spanning-tree root primary as well as secondary.
Reassigning another switch to be the spanning-tree root primary/secondary, will it cause a downtime in the network? If yes, how long?
Thanks,
Christina

I'm assuming PVST (not rapid-PVST nor MST, that should behave better)
It is very hard to give an exact estimate of a downtime. First, it's not going to be a global downtime. You can basically compare the topology with your current root bridge and the one with your new root bridge. The ports that need to block in the new topology will block quickly, in a matter of few seconds. However, the ports that were blocked in the old topology and that need to be forwarding in the new topology will take a little bit more than 30 seconds to become forwarding (15 second listening + 15 second learning phases). The topology change mechanism will age out stale CAM entries in 15 seconds. If you add a little margin for BPDU propagation, I would estimate that you are looking at a connectivity loss of about a minute, in part of your network.
The more blocked ports need to move from the old to the new topology, the most connectivity loss you will experience. Some feature like uplinfast are able to switchover quickly between their uplinks in case of root ID changing and will reduce the downtime dramatically. It's mainly the core bridges that will take time to unblock their port.
Note that you can expect better convergence time when a better root is introduced in the network (you are lowering the numerical value of the secondary root priority so that it takes over the primary) than when the primary root is downgraded into secondary (you increase the numerical value of the primary root so that it becomes worse than the secondary).
Regards,
Francois

Sg-300 - 3750 stack with SPANNING-TREE root problem.

Morning. I think ive configured a few hundred switches, maybe a thousand in my time, but never have a faced such horribleness that is the SG-300. After this week, I think ill refuse to touch them.
Got 2 voice vlans and running a few vrf's on a 3750 stack. but this discussion is about layer 2.
2 x 3750 stacked
1 x voice switch sg-300 company A voice vlan 18 - Po1 up to 3750 distributed etherchannel Po1 (LACP active both sides) 2 ports in channel
1 x voice switch sg-300 company B voice vlan 19 - Po1 up to 3750 distributed etherchannel Po2 (LACP active both sides) 2 ports in channel
Allowed vlans on both sides (command on Port-channel) are data A, Voice A, Mgt A to switch A
Allowed vlans on both sides (command on Port-channel) are data B, Voice B, Mgt B to switch B
It seems that these switches are limited to one voice vlan....
and that spanning tree BPDU's are ignored (or not recevied- havnt released the shark yet). let me explain.
originally when using "smart port" the switch with the lowest mac address, whatever Voice vlan was configured would take over the other switche's voice vlan, argh what a nightmare.
I gave up on the GUI as its far to complcated and have Almost got this working.
I am now using auto voice vlan, but have disabled smart macro. I hope that disabling smart macro stop other switches from learning the switch with the lowest mac address's voice vlan. So far so good - in the LAB. No where was it documented in the cli guide how do disable this stupid feature.
DHCP is working from scope on core, can mange the switches etc etc, access vlan voice vlan all good (after a monster battle).
Now I have an issue with spanning tree.
spanning tree priority for vlans 1-4094 on the 3750 is 4096.
spanning tree priority for vlans 1-4094 on the SG-300's is 6xxxx.
ALL switches think that they are the root. (well the "logical" 3 of them) The 3750's for all vlans, and the SG-300 for the one instance as it doesnt support per vlan. (I am not interested in trying MST here..this is not a datacentre)
On the 3750's Ive tried ieee, pvst, rpvst, while matching the non per-vlan equivalent on the SG series.
What is the difference between a General port and Trunk Port on a SG-300 specific to spanning tree, native vlans (when you can just configure an untagged vlan anyway!!) and what is the relevance to the way the bpdu's are carried?
And why the need for a PVID, when you can tell a port what is tagged and what isnt.
Does the trunk need Vlan1 to be explicitly allowed, and untagged? Does the Po trunk need to be a general port with PVID configured? in vlan 1?
I need to sort this, as cannot put an access switch into production that thinks it is the root of the tree. I wish I had a 2960.... a 3500XL..anything
Does anyone have CLI commands that can help here?

F.Y.I for catylyst heroes - here is the equivalent config for SG-300 - Vlan1 is required on the allowed list on the catylyst side (3xxx/4xxx/6xxx)
In this example:
VLANS - Voice on 188, data on 57, management on 56.
conf t
hostname XXX-VOICE-SWXX
no passwords complexity enable
username xxxx priv 15 password XXXXX
enable password xxxxxx
ip ssh server
ip telnet server
crypto key generate rsa
macro auto disabled
voice vlan state auto-enabled !(otherwise one switch controls your voice vlan….)
vlan 56,57,188
voice vlan id 188
int vlan 56
ip address 10.230.56.12 255.255.255.0
int vlan1
no ip add dhcp
ip default-gateway 10.230.56.1
interface range GE1 - 2
switchport mode trunk
channel-group 1 mode auto
int range fa1 - 24
switchport mode trunk
switchport trunk allowed vlan add 188
switchport trunk native vlan 57
qos advanced
qos advanced ports-trusted
exit
int Po1
switchport trunk allowed vlan add 56,57,188
switchport trunk native vlan 1
do sh interfaces switchport po1
!CATYLYST SIDE
!Must Explicitly allow VLan1, this is not normal for catalysts - or spanning tree will not work ! Even though it’s the native vlan on both sides.
interface Port-channel1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,56,57,189
switchport mode trunk

Spanning tree query for extending existing lan

Hi Guys,
I've got a network setup where I need to add a new set of switches have some new vlans that are independant to the existing environment but i have some of the existing vlans propogate accross.
My current setup is:
and my new design is this:
The 5505-02 is there so that i can easily manage acl's so that only some users can access the new vlans such as 200. And in the future put in idfw to manage this via AD groups.
My concern is regarding spanning tree. The current set up the 3750-01 , 2960-01, sf300-01 and sf300-02 are all set to default pvst where the 3750-01 is the root bridge for all existing vlans
With having the vlan 101 and 102 being propagated across to the new environment what is the best way of tackling STP for this? could I manually set the root primary and the priority to be lowest for these two vlans as the 3750-01? And then the same for the new 200 and 201 as the new 3750-02?
Or would setting a different mode be best i.e mst?
thanks
Rich

Rich
Are you proposing to use the same IP subnet for vlans 101 and 102 on the new switches ?
If so unless the ASA 5505-02 is in transparent mode then you will not be able to extend vlans 101 and 102 across to the new switches ie. if it is in routed mode that is a L3 hop and you generally can't extend a L2 vlan across a L3 hop. There are technologies that allow you to do this but i dont think any of them are supported on the 3750 switches.
If you are making the ASA 5505-02 transparent then it would need to be transparent for a trunk link and i don;t know whether this is possible. You may want to ask in the firewalling forums.
So before worrying about STP can you clarify what you are going to be doing with ASA 5505-02 and that whether or not you are proposing to use the same IP subnet for those vlans on the new switches ?
One last question. Any particular reason why you are using a square topology as opposed to simply using multiple uplinks from each 2960 to the 3750 stack ?
Jon

Which spanning tree protocol is preferred PVST or rapid-PVST and why?

I have WS-C2960G-24TC-L and Cisco 3750G switches, I have option to configure PVST spanning tree or rapid-pvst. Please let me know which is better and why? also send me some document explaining both protocols in detail.

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As Alex has noted, normally rapid-PVST should be preferred.
Depending on needs (and device support), MST might be better yet.

Spanning-Tree MST

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