The FNN (Flat Neighborhood Network) paradox

Bogdan Costescu bogdan.costescu at
Thu Feb 22 05:20:30 PST 2001

On Wed, 21 Feb 2001, Martin Siegert wrote:

> A word of caution:
> Most (all?) switches will get horrendously confused, if you connect
> two (or more) channel bonded NICs to the same switch.
> ...
> Most (all?) switches cannot handle receiving the same MAC address from
> different NICs. Hence if you plan on doing channel bonding buy as many
> switches as you buy NICs/per box and connect each channel bonded NIC
> in a box to a different switch. Even if you can configure your switch
> (using VLANs, etc.) to accept identical MAC addresses from different NICs,
> the setup must be a nightmare.

I'd like to share a different experience: I never had problems with the
described setup. I used 2 NICs to connect to Cisco switches (4000 and 5000
series) and a BayStack 350-24T, using the bonding/trunking facilities of
these switches. The Linux side was configured as described in the channel
bonding docs - same MAC address for both cards. On the BayStack switch I
also tried to define 2 VLANs and use the same setup and it didn't work,
but maybe I wasn't too motivated as the first setup worked... Maybe the
confusion that you mentioned appeared in this "mode", the switch not
supporting identical MAC addresses on non-bonded ports (even in different
My impression was that having identical MAC addresses for the bonded cards
is a must and so it should be supported by all the switches that claim the
bonding capabilities.


Bogdan Costescu

IWR - Interdisziplinaeres Zentrum fuer Wissenschaftliches Rechnen
Universitaet Heidelberg, INF 368, D-69120 Heidelberg, GERMANY
Telephone: +49 6221 54 8869, Telefax: +49 6221 54 8868
E-mail: Bogdan.Costescu at IWR.Uni-Heidelberg.De

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