Router/PVST question...

Answered Question
May 23rd, 2009
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Using NetLabs (from NetAcademy) I hav3 a 2621 Fa0/0 hooked up to a virtual PC using VMware. When I ran a packet sniffer on the virtual pc (troubleshooting a different problem) I saw some PVST+ packets ... the only cable/NIC on this PC is coming from the FA0/0 of the router...my question is why would I be seeing spanning tree packets from from a router?


The config on the router is nothing fancy,

int fa0/0

ip address blah blah

dupl auto

speed auto


Thanks,

Jimmy


Correct Answer by Giuseppe Larosa about 7 years 11 months ago

Hello Jimmy,

real world routers never generate PVST BPDUs, with special configurations (like L2TPV3) they can propagate them in some form of L2 transport over an IP network.

Routers can generate their own BPDUs but of type IEEE 802.1D when configured for Routing and Bridging (IRB).


My guess is that the system use a "switch object" to connect the three routers and the virtual PC to the same vlan (4 ports of a vlan) and it is this object that generates the PVST+ frames you see on the virtual PC port.


Hope to help

Giuseppe


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Correct Answer
Giuseppe Larosa Sun, 05/24/2009 - 01:02
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Hello Jimmy,

real world routers never generate PVST BPDUs, with special configurations (like L2TPV3) they can propagate them in some form of L2 transport over an IP network.

Routers can generate their own BPDUs but of type IEEE 802.1D when configured for Routing and Bridging (IRB).


My guess is that the system use a "switch object" to connect the three routers and the virtual PC to the same vlan (4 ports of a vlan) and it is this object that generates the PVST+ frames you see on the virtual PC port.


Hope to help

Giuseppe


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