It could just part of the way the Omniswitch operates. Back when they came out, Xylan had some of the most innovative ways to use VLANs in the industry.
It's been better than five years since I've touched 'em (they were bought by Alcatel, along with Packet Engine at about the same time) ... but back in the days of many topologies, a Xylan could save an organization some major grief transitioning from one topology/technology to another.
For example, out of the box, you could put in an ATM UNI blade, a Token-Ring blade, an Ethernet blade, a CDDI blade and a FDDI blade into a chassis (with the switch processor) .... plug all of that stuff in, configure the ATM UNI for edge ... and everything would talk to everything else.
You could create VLANs such that the switch would automatically put you in the correct VLAN (sort of like VMPS, but this worked, and was years ahead of VMPS), put you in a VLAN based on authentication (originated from the switch), multiple VLANs per port, port groups, VLAN by protocol (IP, IPXS, Appletalk ...all automatic).
Xylan was a pretty neat switch, I have no idea what Alcatel's done with them since ... maybe their OK, maybe they're not.
I'm digging around to see if we still have docs in the Lab, I suspect not, but I promise to look.
Try things (if you haven't) like putting the mirrored port in the same VLAN as the monitored port, put the monitoring PC on the same IP block (I know it shouldn't matter in promiscuous mode, but try it), as the monitored (and mirrored) ports.
Try another PC and / or NIC in the monitoring machine, may it just doesn't like promiscuous mode.
Try changing the NIC parameters on the monitoring machine. Maybe the problem isn't the Xylan / router at all.
It's a goofy problem. For goofy problems, all you can do is to start ruling-out things one at a time. If you hit the end of the list, give up.
Good Luck
Scott
