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Date:   Wed, 15 Jul 2020 23:02:26 +0200
From:   Ian Kumlien <>
To:     Jakub Kicinski <>
Cc:     Linux Kernel Network Developers <>,,
Subject: Re: NAT performance issue 944mbit -> ~40mbit

On Wed, Jul 15, 2020 at 10:31 PM Jakub Kicinski <> wrote:
> On Wed, 15 Jul 2020 22:05:58 +0200 Ian Kumlien wrote:
> > After a  lot of debugging it turns out that the bug is in igb...
> >
> > driver: igb
> > version: 5.6.0-k
> > firmware-version:  0. 6-1
> >
> > 03:00.0 Ethernet controller: Intel Corporation I211 Gigabit Network
> > Connection (rev 03)
> Unclear to me what you're actually reporting. Is this a regression
> after a kernel upgrade? Compared to no NAT?

It only happens on "internet links"

Lets say that A is client with ibg driver, B is a firewall running NAT
with ixgbe drivers, C is another local node with igb and
D is a remote node with a bridge backed by a bnx2 interface.

A -> B -> C is ok (B and C is on the same switch)

A -> B -> D -- 32-40mbit

B -> D 944 mbit
C -> D 944 mbit

A' -> D ~933 mbit (A with realtek nic -- also link is not idle atm)

Can it be a timing issue? this is on a AMD Ryzen 9 system - I have
tcpdumps but i doubt that they'll help...

> > It's interesting that it only seems to happen on longer links... Any clues?
> Links as in with longer cables?

Longer links, as in more hops and unknown (in this case Juniper) switches/boxes

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