Cisco MSTP

Unanswered Question
Oct 10th, 2003

Hi all:

Is Cisco's implementation of MSTP/RSTP compliant with the IEEE Specs (802.1s/w) ? If now, how does it differ?

Any help is appreciated.

Thanks,

Vishal

I have this problem too.
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tsettle Fri, 10/10/2003 - 15:09

In the documentation it is stated that the MST feature is based on a 802.1s draft - when the code came out that's the state the spec was in. What the specific differences are, I don't know.

From http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw_8_1/confg_gd/spantree.htm#1155281

"The MST feature for this release is based on a draft version of the IEEE standard. MST is backward compatible with 802.1D STP, 802.1w, the Rapid Spanning Tree Protocol (RSTP), and the Cisco PVST+ architecture."

vzinjuvadia Fri, 10/10/2003 - 22:51

Thanks for your reply. I have one more question for you. The document you sent seems to be pretty recent (July 2003) which means it was referring to the latest version of the MSTP draft. The specific question I have is with respect to the configuration digest carried in the MSTP BPDU. The draft suggests that the Configuration digest is calculated using HMAC-MD5 algorithm. It also provides some sample digests for particular vlan to MST instance mappings. However it appears that the Configuration digest carried in Cisco's MSTP BPDU does not match with the samples provided in the IEEE draft. What algorithm does Cisco use to generate the Configuration Digest?

Your help is much appreciated.

Thanks,

Vishal

bsivasub Mon, 10/13/2003 - 21:11

Cisco implementation will fully comply with final IEEE spec in a future release (For ex: 8.3 for CatOS ). Current version is based on a earlier draft. It was introduced in 7.1 release.

Please open a TAC case for further discussion on this issue.

vzinjuvadia Fri, 10/24/2003 - 14:56

Thanks for you reply. What IOS release will support the final IEEE spec?

Regards,

Vishal

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