MST issue

[mohammedrafiq]

Hi All,

I am having some issue with SPT with the following topology (see attached).

Pair of Nexus 5548 and 3750  are configured with MST instance 1.when enable STP as MST on Dell switches , it does not recognise it and create loop but if We change MST0 (only tried on one 3750 and two Dell switches in triangle in lab). its work fine.

Does Dell switches only understand MST0 ?

Can Nexus 5548 support MST0 if we change from MST1 and what will be effect?

spanning-tree mst configuration

name DC1

revision 1

instance 1 vlan 1,3,10

Regards.

[JohnTylerPearce]

I wonder if the BPDUs are incompatible? What is the model number of the dell switches that you have?

[swordcrowned]

Mohammed,

In order for a MST instance to form, the instance # and revision # must be the same.  If you are unable to set these on the Dell Switch, then you will not be able to form a MST instance. The attributes for the Instance must match.  It work on MST0, because that is treated like regular SPT and the Dell switch can understand that.  Check out this link for everything you could possibly ever want to know about MST.

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfc.shtml

Bryan Hefner

[mohammedrafiq]

Hi,

The Dell switches model number is  8024F.

Reards.

[swordcrowned]

Mohammed,

The 8024F is compatible with 802.1s and should work.  Make sure you issue the "spanning-tree mode MSTP" on the dell switch.  Also, for adding vlans into the instance, use the "instance 1 ADD vlan X" command under the 'spanning-tree mst configuration'.  Outside of that, as long as the parameters match, then it should work just fine.

Bryan