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VIP Green

Number of Supported Spanning tree instances

My clients switch is running out of Spanning-Tree instances (c3560 only supports 128 instances).  I know that running RSTP with VSTP can help mitigate this that all instances over 128 will be handeled by RSTP, but before I implement this are there any other thoughts out there on how to mitigate this.  Would MSTP be able to handle more STP instances or MISTP perhaps?

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Accepted Solutions
VIP Super Bronze

Re: Number of Supported Spanning tree instances

MST can handle up to 16 instance (0 to 15), but usually you only need one instance for all your vlans unless you have a lots of vlans and are planning to divide them in multiple instances.

http://www.cisco.com/en/US/docs/ios/lanswitch/command/reference/lsw_s2.html#wp1111112

HTH

Cisco Employee

Re: Number of Supported Spanning tree instances

Hello Reza and Marius,

The MSTP should indeed be the answer to Marius' needs. It should be particularly stressed that the number of concurrent MST instances is a value independent to the number of VLANs. It is possible to have thousands of VLANs, and yet use just two MST instances and have all these VLANs divided and mapped among the two MST instances. There is usually no reason to use more than a few MST instances.

In more recent MSTP implementations, the maximum number of concurrent MST instances has been increased to 65 with the range of MSTP instance numbers being 0-4094, see:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_58_se/configuration/guide/swmstp.html#wp1073881

I am not aware of the VSTP - can anybody enlighten me what it is? Regarding the MISTP, that has been a very, very early predecessor of the modern MSTP and is not supported on any recent switch to my best knowledge.

Best regards,

Peter

3 REPLIES
VIP Super Bronze

Re: Number of Supported Spanning tree instances

MST can handle up to 16 instance (0 to 15), but usually you only need one instance for all your vlans unless you have a lots of vlans and are planning to divide them in multiple instances.

http://www.cisco.com/en/US/docs/ios/lanswitch/command/reference/lsw_s2.html#wp1111112

HTH

Cisco Employee

Re: Number of Supported Spanning tree instances

Hello Reza and Marius,

The MSTP should indeed be the answer to Marius' needs. It should be particularly stressed that the number of concurrent MST instances is a value independent to the number of VLANs. It is possible to have thousands of VLANs, and yet use just two MST instances and have all these VLANs divided and mapped among the two MST instances. There is usually no reason to use more than a few MST instances.

In more recent MSTP implementations, the maximum number of concurrent MST instances has been increased to 65 with the range of MSTP instance numbers being 0-4094, see:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_58_se/configuration/guide/swmstp.html#wp1073881

I am not aware of the VSTP - can anybody enlighten me what it is? Regarding the MISTP, that has been a very, very early predecessor of the modern MSTP and is not supported on any recent switch to my best knowledge.

Best regards,

Peter

VIP Green

Number of Supported Spanning tree instances

Thanks for the replies! and yes I was thinking MSTP would be the way to go, but just wanted to see if there were any other options to consider.

VSTP stands for VLAN Spanning-tree Protocol.  It is the Juniper implementation of spanning tree if required to be compatible with Cisco's spanning tree.  I threw it out there just to show that I am open to suggestions of changing hardware if needed.

Thanks for your input!

Regards,

Marius

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