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

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?


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.


Same thing with Siemens and Huawei gear, there are "transparent" cards that
don't learn anything and L2 cards that do.

I think we narrowed it down to a cheap media converter they supplied.
It's a 10/100/1000 copper to gig fiber converter, which makes me think
it's got a low grade switch inside that doesn't have a per-VLAN FDB.

Fuji 4500 gear, depending on the card, software release, and configuration,
can support or not support tagged traffic, which might also be
distinguishing aspect that your vendor may not be aware of.

Let me know if you need a bit more details, and I can ask our consultant who
works with these boxes on a regular basis.