11-29-2012 01:08 AM - edited 03-07-2019 10:18 AM
Dear All,
How PVST works?
can anyone explain woth the help of an example?
Thanks,
Vishal
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12-04-2012 04:58 AM
Hi,
acually, each switch believes to be an STP root until it receives a BPDU with better priority than its own one within the VLAN.
Is it clear now?
HTH,
Milan
11-29-2012 01:34 AM
Hi,
PVST is just STP but with an STP instance for each VLAN and by default all VLANs wiil follow the same STP topology but you can configure your switches so that there is a different STP topology per VLAN.
If you need more info on STP then we'll be glad to help.
Regards.
Alain
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11-29-2012 04:57 AM
Dear Alain,
Thanks for the reply!!! Now suppose there are 10 switches running vlan 1, 10 and 20...
Now, for each vlan there is separate instance of STP on all switches or
each vlan has separate instace of STP on individual switches?
11-29-2012 05:24 AM
Hi,
a separate instance per VLAN on each switch.
Regards.
Alain
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11-29-2012 08:44 PM
11-29-2012 11:26 PM
Hi,
check the STP for VLAN 99 by sh spanning-tree vlan 99 commands on both switches.
You might see either of them having not the default STP priority configured for that VLAN.
Possibly your 223 swict had been configured as the STP root for VLAN 99 in the past?
HTH,
Milan
12-01-2012 01:22 AM
hi milan,
all the values are at their deafault only
12-01-2012 01:14 PM
Can you post the output of the 'sh spanning-tree vlan 99' please.
Thanks,
Adam
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12-02-2012 10:41 PM
Dear Adam,
Below is the output for show spanning tree for vlan 99 of all the switches
220
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f9ce.xxxx
219
VLAN0099
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f9ce.xxxx
238
VLAN0099
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
237
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 34bd.c8b6.xxxx
236
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 203a.07fb.xxxx
235
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 34bd.c8f6.xxxx
234
VLAN0099
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f98c.xxxx
227
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
228
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f9ce.xxxx
229
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
230
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
231
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
232
Address 0024.f98c.xxxx
Cost 32
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
233
Root ID Priority 32867
Address 0024.f98c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
253
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address 001d.7040.xxxx
221
Root ID Priority 32867
Address 0024.f91c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f91c.xxxx
222
Root ID Priority 32867
Address 0024.f91c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f98c.xxxx
223
Root ID Priority 32867
Address 0024.f91c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f9c4.xxxx
223
Root ID Priority 32867
Address 0024.f91c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f9c4.xxxx
225
Root ID Priority 32867
Address 0024.f91c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
226
Root ID Priority 32867
Address 0024.f91c.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
240
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address e8ba.7084.xxxx
241
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f91c.xxxx
244
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
245
spanning tree instance d oes not exist
246
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
247
spanning tree instance d oes not exist
248
Root ID Priority 32867
Address 001d.7040.xxxx
Cost 4
Bridge ID Priority 32867 (priority 32768
Address 0024.f9cd.xxxx
239
Root ID Priority 32867
Address 18ef.6350.xxxx
Bridge ID Priority 32867 (priority 32768
Address 18ef.6350.xxxx
249
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f761.xxxx
250
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
242
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f91c.xxxx
251
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0025.4610.xxxx
252
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f761.xxxx
243
Root ID Priority 32867
Address 001d.7040.xxxx
Bridge ID Priority 32867 (priority 32768
Address 0024.f98c.xxxx
12-03-2012 12:54 AM
Hi,
which of the switches is your 4506?
Switch 253?
What does show spanning tree 99 show on it?
Istn't ther epossible youe VLAN 99 is discontinous somewhere?
In that case you would see two STP roots - each for one part of the discontinous VLAN 99!
HTH,
Milan
12-03-2012 04:50 AM
yes Milan, 4506e is 253. and there is discontinuity. But my doubt is root bridge is elected among all the switches.. am I right?
Please educate me!!!!
12-03-2012 05:34 AM
No,
the root is elected per VLAN among the switches which can "see" each others.
So for a discontinous VLAN you've got two roots finally - one per each continuous part of the VLAN.
HTH,
Milan
12-04-2012 02:11 AM
Dear Milan,
Instead of saying can see each other, can we say which are connected in loop or in chain?
12-04-2012 03:58 AM
Hi,
no we should say which see each other's BPDUs for the coresponding vlan instance.
Regards.
Alain
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12-04-2012 08:10 PM
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