Re: interesting troubleshooting

[Saku Ytti <saku () ytti fi>]

On Sat, 21 Mar 2020 at 04:20, Steve Meuse <smeuse () mara org> wrote:

> What that large flow in a single LSP? Is this something that FAT lsp would fix?

No.

FAT adds additional MPLS label for entropy, ingressPE calculates flow
hash, based on traditional flow keys and injects that flow number as
MPLS label, so transit LSR can use MPLS labels for balancing, without
being able to parse the frame. Similarly VPN provider could do that,
and inject that flow hash as SPORT at the time of tunneling, by
looking at the inside packet. And any defensive VPN provider should do
this, as it would be a competitive advantage.
Now for some vendors, like Juniper and Nokia transit LSR can look
inside pseudowire L3 packet for flow keys, so you don't even need FAT
for this. Some other like ASR9k cannot, and you'll need FAT for it.

But all of this requires that there is entropy to use, if it's truly
just single fat flow, then you won't balance it. Then you have to
create bias to the hashResult=>egressInt table, which by default is
fair, each egressInt has same amount of hashResults, for elephant
flows you want the congested egressInt to be mapped to fewer amount of
hashResults.

-- 
  ++ytti