What is the default spanning tree protocol used in cisco?

[shahul-hameed]

Hi all,

What is the default spanning tree protocol used in cisco?

Regards,

Shahul

[Georg Pauwen · Accepted solution]

Hello Shahul,

it depends on the model, most Cisco switches run PVST+ by default. Which model do you have ?

Regards,

GP

[shahul-hameed]

Hi gp,

Thankyou for your immediate response.We are using cat6500.Can u define me whats designated switch and how is it elected on the stp process if we are using pvst & pvst+.I have posted a question but iam not able to understand the answer i got.If you could plz help me in this.Once i get the answer for this i will can mark this as finished.

Awaiting an early relpy & thankingyou.

Regards,

Shahul

[Georg Pauwen]

Hello Shahul,

The default on the Cat6500 is PVST.

PVST+ is just an extension of PVST, which allows non-PVST information to be accepted and received into PVST. So PVST+ is mainly used to allow Cisco switches to interoperate with non-Cisco switches (keep in mind that PVST is Cisco-proprietary). PVST uses Cisco-proprietary ISL on trunks, whereas PVST+ allows 802.1Q.

Regarding the selection of the designated switch: in PVST mode, one designated switch is selected per VLAN. The designated switch is simply the switch closest to the root switch through which frames are being forwarded to the root.

Does that make sense ? Let me know if things are not clear yet...

Regards,

GP

[shahul-hameed]

Hi GP,

Thankyou verymuch for the explanation for PVST.And reg. the designated switch i didn't understand - the switch closest to the root switch through which frames are being forwarded.Can u please expalin me.

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_configuration_example09186a008009467c.shtml#prereq

Here there is an example.

Reg. root switch its clear.But reg. designated switch iam not clear.If you could plz help me in this.Iam so sorry for making you irritated.But iam still in confusion reg. this designated switch.If possible plz send me some cisco link where designated switch is explained in detail.As soon as i get my answer i will post my issue resolved.Thankyou very much for doing this favour Mr.GP.

Regards,

Shahul

[Georg Pauwen]

Hello Shahul,

try to look at it this way: per VLAN, there can only be one valid path to the root switch. In this scenario:

Root Switch <-> Designated Switch <->

The designated switch is the switch directly connected to the root switch. The port on the designated switch pointing to the root switch is the root port. The port on the designated switch pointing away from the root switch is the designated port...

HTH,

GP

[shahul-hameed]

Hi GP,

Now you cleared my doubt exactly.Thankyou somuch.But the default spanning tree in cat6000 is pvst+.

Regards,

Shahul