Don't know the FlashWave gear well, but in the Cisco ONS/Cerent world GigE ports can be configured in different modes, some of which do in fact learn MAC addresses. Others emulate a single layer-2 link and as the vendor stated, would not look at the MAC address at all. -Scott -----Original Message----- From: Jay Nakamura [mailto:zeusdadog@gmail.com] Sent: Wednesday, December 08, 2010 3:33 PM To: NANOG Subject: SONET and MAC address We have a Gigabit Ethernet transport between cities by a vendor. We found that when there are identical MAC address that are on different VLANs on different side of the circuit, one of the VLAN looses packets. This situation came up because two different networks that travel over the Ethernet were using HSRP with the same virtual MAC address. The vendor says both sides are directly connected to Fujitsu SONET gear and the equipment doesn't even look at the MAC address so it's not their circuit. All I know is, I can't recreate the problem if this circuit is not in the path. I haven't worked with Fujitsu SONET gear so I don't know if their claim is true or not. I vaguely remember someone talking about some equipment actually having a builtin switch on the SONET port and that was messing up the forwarding. Also, on one side of the circuit, there is a copper to fiber media converter. I am going to find out what model this is and see if that could be the cause. Anyone have any thoughts on what I should look into or have the vendor look into? Anyone run into this situation? Thanks!