netdev - Re: Debugging stuck tcp connection across localhost [snip]

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Message-ID: <CANn89iK2iM=fM=EN3v3jfOfHRS4HKzbShLcnHt78U+OjnmeVjg@mail.gmail.com>
Date:   Wed, 12 Jan 2022 10:47:16 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Ben Greear <greearb@...delatech.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: Debugging stuck tcp connection across localhost [snip]

On Wed, Jan 12, 2022 at 10:44 AM Ben Greear <greearb@...delatech.com> wrote:

> Well, I think maybe I found the problem.
>
> I looked in the right place at the right time and saw that the kernel was spewing about
> neigh entries being full.  The defaults are too small for the number of interfaces
> we are using.  Our script that was supposed to set the thresholds higher had a typo
> in it that caused it to not actually set the values.
>
> When the neigh entries are fully consumed, then even communication across 127.0.0.1
> fails in somewhat mysterious ways, and I guess this can break existing connections
> too, not just new connections.

Nice to hear this is not a TCP bug ;)

>
> We'll do some more testing with the thresh setting fix in...always a chance there is more than one
> problem in this area.
>
> Thanks,
> Ben