switch for channel bonding

Bogdan Costescu Bogdan.Costescu at IWR.Uni-Heidelberg.De
Fri Aug 18 10:44:03 EDT 2000


Hi,

AFAIK Cisco calls "channel-bonding" what others call "trunking". I have
used Cisco 5000 series' "channel-bonding" and BayNetworks 350-24T's
"trunking" facilities and they worked just the same. Whatever it's called
it's supposed to do this: allow bundling of several physical links into a
logical one. To do this, they require that all the NICs at the other end
have the same MAC (Ethernet address).

It's not possible to split one packet among the physical links, but
different packets can go through different links. The decision of which
link to use for sending a packet is completely up to the device (switch or
Linux host, not the NIC) and there may be different strategies. For
example the Linux "channel-bonding" module presently uses a Round-Robin
strategy, where the packet "i" is sent through the link i % n (i modulo
n), where "n" is the number of physical links available. At the Rx end,
the packets from "ethx" are all sent to the bonding module (in the order
they were received), and the upper levels just see the packets coming from
"bond0".

The bonding facility was introduced in the 2.2 series earlier this year 
and was recently modified. It can be used to bond 2 or more NICs (the
maximum number is not a limit of the bonding module AFAIK) - usually the
switch limits the number of physical links that can be bonded (4 for some
Cisco switches and for BayNetworks 350). You can bond different brands of
NICs (e.g. a 3Com, a DEC-based and a EEPro), the bonding module doesn't
care about this; however, for getting good results, the bonded NICs should
be similar in performance. And no, you don't need any patches for the
network drivers; I suppose that one of the things that was present in the
patches that you mention was the abillity to set the Ethernet address;
nowadays, all the network drivers that I know of allow this.

To come back to the original question: there are quite a lot of switches
that allow "channel-bonding"/"trunking"/whatever is called. I know of
quite a lot of the Cisco switches, the 3900 switches from 3Com,
BayNetworks 350 and 450, some Intel switches. Usually, this facility is
mentioned in the white-paper of the switch, so just searching on the web
sites of these (and maybe other) manufacturers might give you the answers;
also usually they write a lot about how beneficial this facility can be to
you, so it's quite hard to miss it.
Mr. Thomas Davis (tadavis at lbl.gov) wrote in the README accompanying the
bonding module that he would like to put together a list of switches
reported to work with it (based on the feedback from the users...)
However, I don't know if this list exists.

Sincerely,

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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