SONET and MAC address

Jay Nakamura zeusdadog at
Wed Dec 8 18:33:11 CST 2010

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.

On Wed, Dec 8, 2010 at 5:46 PM, Danijel <theghost101 at> wrote:
> Same thing with Siemens and Huawei gear, there are "transparent" cards that
> don't learn anything and L2 cards that do.
> --
> *blap*
> On Wed, Dec 8, 2010 at 22:57, Scott Berkman <scott at> wrote:
>> 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 at]
>> 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!

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