We run a Catalist 6513 with some 30+ vlans configured and four SVIs for different vlans. Today I wanted to test SPAN with an entire vlan, without SVI, as source and a gigEther port as the destination. On the receiving end was a server running Ethereal. I've been using this setup several times to diagnose network errors but never with an entire vlan as source.
I was amazed to see traffic from other vlans, some not even remotely related, appearing in Ethereal. This monitoring session has no other source active and when I disable the source in the monitoring session Ethereal goes quiet.
I was under the impression that traffic in one vlan was isolated from the other. Or is this something that relates to SPAN configuration only?