brain teaser physically connecting layer 2 switch link to layer 3 switch link

[gbraver]

Our network suffered a significant event today and have been wondering about root cause.  Shouldn't the layer 3 side just drop bpdu packets and not forward any.

[Dennis Mink]

what are you talking about?

[Vivek Ganapathi]

Please elaborate.

[gbraver]

sample configuration

one end

int gig 1/1

no switchport

no ip address

on the other end

int gig 1/1

switchport mode access

switchport access vlan 5

spanning-tree portfast

should this be transparent/non-functional or should it cause network issues

[Mitchell Kelly]

Non-functional.

The first switch configuration has the port set as a routed port: no switchport, this needs an IP address to communicate. Has this answered your question?

[danrya]

To answer you original question:

Yes, the L3 port would drop BPDU's, BUT with your configuration the L2 switch is configured as an Access port and would never send any BPDU's.

So, to answer your second question, this configuration is invalid and would result in a "line protocol down" on the L3 interface side since there's no ip address assigned to the interface.