Specifications

Understanding How Spanning Tree Operates

March 14, 2011 Page 10 of 29

switchingdevice2istherootforMSTI2,andswitchingdevice5istheCISTregionalroot.Traffic

foralltheVLANsattachedtoanMSTIfollowtheMSTI’sspannedtopology.

Variousoptionsmaybeconfiguredonaper‐MSTIbasistoallowfordifferingtopologiesbetween

MSTIs.Toreduce

networkcomplexityandprocessingpowerneededtomaintainMSTIs,you

shouldonlycreateasmanyMSTIsasneeded.

Figure 4 MSTI 1 in a Region

Figure 5 MSTI 2 in the Same Region

Figure 6shows3regionswithfiveMSTIs.Table 3definesthecharacteristicsofeachMSTI.Ports

connectedtoPCsfromdevices1,3,9,and11willbeautomaticall ydetectedasedgeports.

Devices

4and10aretheCISTregionalrootsand,becausetheycontainthemasterportfortheirregions,are

alsotheregionalrootdevices.EachMSTIcanbeconfiguredtoforwardandblockvariousVLANs.

MSTI 1

MST CIST

Regional Root

MSTI 1 Regional Root

Physical Link

Legend:

Blocked VLANs

CIST Root

MSTI 2