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

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Message-ID: <05ae90a3-4fc4-45aa-c001-fb26334332c4@candelatech.com>
Date:   Wed, 12 Jan 2022 10:54:05 -0800
From:   Ben Greear <greearb@...delatech.com>
To:     Eric Dumazet <edumazet@...gle.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 1/12/22 10:47 AM, Eric Dumazet wrote:
> 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 ;)

For sure...it took me a long time to get brave enough to even suggest it might
be on a public list :)

That said, might be nice to always reserve a neigh entry for localhost
at least...can't be that hard to arp for it!

--Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com