> Hi -
> We own one NAS box, and are evaluating another, that offer dual GigE
> NICs operating as a 'bonded pair'. These connect to an HP switch that
> supports port trunking. There is some confusion about just how this
> bonding occurs, but one of the mfr's seems to think it's FEC.
> Each of these boxes (running RH Linux) creates a logical interface
> named 'bond0', which has as its elements 'eth1' and 'eth2', the physical
> NICs. In each case the two NICs are assigned the same IP address.
> But in one of these boxes, the individual NICs also have the same MAC
> address, where the other one has sequential MAC addresses for the two
> So the question is, which is preferable, assuming that this is really
> FEC? Both mfr's claim that they just hook these up to a switch and
> there are "no problems". Well, wrong. The box with the different MAC
> addresses seems only to use one interface, while the other one idles.
> The box with the identical MACs balances its load between the NICs, but
> is clearly not performing at its best... pulling one cable actually
> speeds up access.
> Any thoughts?
I have some detailed(ish) knowledge of Cisco stuff.
Over the years cisco have supported various methods of selecting a
the transmission of a particular frame.
These have included the, XOR of the last [log2 of n bits] of one of
MAC addresses, method originally used.
As I recall a more sophisticated hash of the addresses is now done on
at least some platforms - I don't know if the method has been made
source MAC or IP
dest MAC or IP
src + dst MAC or IP with a more sophisticated hash than above.
Cat 6000 on CatOS software apparently does:-
EtherChannel load balancing can use either MAC addresses or IP
and either source or destination or both source and destination
The selected mode applies to all EtherChannels configured on the
All of these schemes guarantee that a particular half conversation
uses a particular path. This maintains packet order in each stream.
While out of order packet would not necessarily cause applications to
fail, I suspect that it may result in an increase in processing
for the data stream.
The point of all of the discussion is that various schemes are
I am not surprised by the difficulty in obtaining a reliable statement
of the principles of operation of this sort of equipment. This has
been my own
experience in the past with various vendors. Just sign here sir:-)
Getting your sniffer out has often been the only reliable way of
resolving sort of this issue.