[f-nsp] linux 802.3ad bonding with foundry switch

[Nick Hilliard]

On 23/09/2011 09:19, Jethro R Binks wrote:
> I'm a bit hazy on details now, but given the scenario of a single client 
> trying to multiplex essentially one traffic stream to a single server over 
> aggregated links, would that have been doable with a Foundry device?  
> Something about "mode 0" at the Linux end rings a bell.

802.3ad link aggregation usually load shares traffic over multiple links by
calculating a hash of certain data in the packet header and using the
result to force packets with that particular hash over a specific link.
Typically the hash would look at src / dst mac and ip addresses.  However,
better hardware will look right inside ipv4 and ipv6 headers.

This typically means that single data streams are intentionally routed down
specific links.  As a result, if you have a LAG between a single client and
single server, and you're running a single data stream between the two
devices, then no hashing algorithm is going to be able to load balance the
traffic in a functional way.

Foundry's link aggregation hashing mechanisms are generally rather good.
But you need to understand that the purpose of the hashing algorithm is to
ensure that discrete data streams are forcibly maintained on specific links
in order to ensure that you don't get out-of-order packets.

Nick