Re: Best practices for cxgbei and link aggregation?

On Thu, Aug 3, 2023 at 2:14 PM Eugene Grosbein <eugen@grosbein.net> wrote:
>
> 04.08.2023 0:56, Alan Somers wrote:
>
> > I'm trying to build a high-speed iSCSI server.  I have two Chelsio T6
> > cards providing 4x 25GbE ports.  I have a requirement for
> > high-availability networking, and I also need multiple ports' worth of
> > bandwidth.  What's the best way to use them?
> >
> > First I tried LACP, of course.  That works.  But it doesn't work in
> > combination with cxgbei iSCSI offload.  The clients can't connect.
> > This makes sense, because the offload engine probably requires all
> > packets from a single iSCSI session to enter and leave through the
> > same network port.  With LACP, that won't be the case.
>
> This is a common misunderstanding. In fact, LACP has nothing to do with per-port
> traffic distribution. Used kind of hashing function is not a part of LACP.
> You just need to use link partners capable of good hashing.
>
> For example, FreeBSD lagg(4) hashing function is capable of using L2 (MAC), L3 (IP) and L4 (TCP/UDP ports)
> headers and any kind of combination of such headers to make sure that packets if single flow go out
> using same port. Take a look at ifconfig.8 manual page for "lagghash".

For iSCSI, any combination of those hash settings should result in a
flow that is always tied to a single port.  But for cxgbei to work, I
need to ensure that the switch also hashes flows in the same way, to
the _exact_same_port_.  Even if I had access to the switch's LACP
configuration, which I do not (but perhaps could acquire), is there
any guarantee that it would hash things the same way as FreeBSD?  Is
the LACP hashing algorithm standardized?