PVST with do1q encapsulation?????

azmath.hk · ‎02-01-2007

Hi,

our switch has been configured PVST with dot1q encapsulation on trunk port....

Since PVST is incampatable with dot1q encapsulation, how this switch has been working from long time?

Please need your valuable inputs...

Khan.

azmath.hk · ‎02-01-2007

waiting for your valuable comments

devang_etcom · ‎02-01-2007

i think this link will help you more:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121t/121t3/dtbridge.htm#wp1020686

regards

Devang

azmath.hk · ‎02-01-2007

Devang,

It does not talk about PVST with dot1q...

My question is why PVST is working with dot1q trunk?

bjw · ‎02-01-2007

Khan,

If your referring to PVST+ in CAT0s/IOS, then it does work with Dot1Q.

Dot1Q is a trunking protocol encasulation, and just provides a common pipe for vlan traffic.

PVST+ is a spanning tree protocol that prevents L2 loops.

See the following ref:

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a00807b0670.shtml#PVST

azmath.hk · ‎02-01-2007

I am using PVST not PVST+...

My question is why PVST is working with dot1q?

In our switch network someone by mistakenly configured PVST on a switch and on its trunk port is configured as a dot1q encapsulation...how come its layer 2 connectivity is up when PVST is incompatable with dot1q encapsulation

Regards,

Khan.

azmath.hk · ‎02-01-2007

Please help me undersand my previous question...

azmath.hk · ‎02-01-2007

please

bjw · ‎02-01-2007

By chance, is there only 1 active vlan active on the switch?

switch> show vlan trunk

azmath.hk · ‎02-01-2007

We have 3 vlans running on this switch..By the way switch model is 2950....I am confuse plase help me out..

azmath.hk · ‎02-01-2007

the command you mentioned is not working on this switch..

Francois Tallet · ‎02-01-2007

On switches, PVST was enhanced to PVST+ as soon as Cisco supported 802.1Q. So you cannot be running PVST on dot1Q trunk, that is necessarily PVST+.

When you say that PVST is not compatible with 802.1Q, is it just a theoric question or do you have a particular problem you want to share with the group?

Regards,

Francois

bjw · ‎02-01-2007

Can you post the output of your show spanning-tree command on the subject switch?

bjw · ‎02-01-2007

Are you on IOS or CATos, what is the CAToS/IOS version, what type of switch is it?

A show ver command output might help.

azmath.hk · ‎02-01-2007

I have attached show spanning-tree and show runn output....please advice

here is the show version

System returned to ROM by power-on

System image file is "flash:/c2950-i6q4l2-mz.121-14.EA1a.bin"

cisco WS-C2950G-24-EI (RC32300) processor (revision H0) with 20710K bytes of mem

ory.

Processor board ID FOC0803W1T9

Last reset from system-reset

Running Enhanced Image

24 FastEthernet/IEEE 802.3 interface(s)

2 Gigabit Ethernet/IEEE 802.3 interface(s)

32K bytes of flash-simulated non-volatile configuration memory.

Base ethernet MAC Address: 00:0F:23:96:8A:40

Motherboard assembly number: 73-7280-05

Power supply part number: 34-0965-01

Motherboard serial number: FOC08032979

Power supply serial number: DAB08020HAX

Model revision number: H0

Motherboard revision number: A0

Model number: WS-C2950G-24-EI

System serial number: FOC0803W1T9

Configuration register is 0xF