ng_fec and cisco 2931

Lars Erik Gullerud lerik at
Wed Mar 2 17:58:07 GMT 2005

On Sun, 27 Feb 2005, Lister wrote:

> I have setup ng_fec on a machine with a quad ethernet NIC :
> I have all 4 ports connected to the catalyst. From what I have read on
> fast etherchannel in the cisco docs, it is supposed to detect the 
> etherchannel,
> e.g. no commands at the switch. Lights blink on and off, change color
> (orange -> green) and it seems to work ... but only on one interface in the
> bundle. No faster than 80Mb. I have a 1000Mb intel card in the 2nd
> test machine that does run much faster than 100.
> So, is there something I have done wrong, or what? What should I expect
> to get from 4 x 100 Mb ports?

Not really related to FreeBSD's ng_fec at all I think, this is a common 
FEC issue.

If you are testing this between two hosts as you indicate above, then you 
are getting exactly the speed you should be getting. The low-end Cisco 
switches offers two varieties of "load-balancing" over the FEC members, 
source or destination-based hash (both operate on MAC-address level). So 
if all your test traffic goes between a set of two mac-addresses, traffic 
in either direction will only flow over one member of the FEC.

The higher-end devices like the 6500 series can also look at layer 3 and 
layer 4 flow-information to distribute the load, but basically a FEC is 
mostly useful in scenarios where you have a large number of hosts 


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