RE: is odd number of links in lag group ok

["Jakob Heitz (jheitz)" <jheitz () cisco com>]

Many routers do not rehash everything when a link breaks.
Doing so would disturb flows that were not broken, causing possible
misordered packets or jitter.
The flows on the broken link will get rehashed, of course.

Note that even if a hash function can distribute the flows evenly,
you may get some heavy flows, so you need to expect some imbalance.

Regards,
Jakob


-----Original Message-----
From: Ben Cannon <ben () 6by7 net>

It will work fine if you have a good modern router.   Consider this; all evenly grouped LAGs are odd in their failed 
conditions.

-Ben

> On May 15, 2018, at 8:28 AM, Mark Tinka <mark.tinka () seacom mu> wrote:
>
>
>
> > On 15/May/18 17:20, Jared Mauch wrote:
> >
> > Much of this depends on the hardware, software and what hashing is used inbound
> > outbound traffic directions, etc.
> >
> > It will likely work the way you expect, but one may be warmer than the other if
> > traffic ends up overloading a single bucket in the hash.
>
> We haven't had a major issue when loading traffic over even or odd
> links. If you have decent hardware and software, it should all be fine,
> particularly if your traffic is all or mostly IP.
>
> If you've got non-IP traffic in there, and your box cannot look into the
> payload to determine entropy, then things could get interesting. But
> this will happen even when you have even links... it's not anything
> specific to how many member links you have in the LAG, but rather, the
> router's need to maintain per-flow load balancing with limited
> information beyond Layer 2 data.
>
> That said, an even number of links just leaves the warm & fuzzies turned
> on :-)...
>
> Mark.