netdev - Re: RACK not getting disabled

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1505769494.29839.34.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Mon, 18 Sep 2017 14:18:14 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     hiren panchasara <hiren@...ugglingcoder.info>
Cc:     netdev@...r.kernel.org
Subject: Re: RACK not getting disabled

On Mon, 2017-09-18 at 13:14 -0700, hiren panchasara wrote:
> Hi all, I am trying to disable rack to see 3dupacks in action during
> loss-detection but based on the pcap, I see that it's still trigger
> loss-recovery on the first SACK (as if RACK is still enabled/active).
> 
> Here is what I did to disable rack:
> net.ipv4.tcp_recovery = 0
> 
> I've also disabled metrics:
> net.ipv4.tcp_no_metrics_save = 1 
> And also flushed existing entries with 'ip tcp_metrics flush' just to be
> on a safer side.
> 
> Not really relevant here but I've also switched to reno.
> 
> I am on: 4.10.0-33-generic
> pcap: https://transfer.sh/mfoiN/reno_no_rack.pcap
> 
> What am I missing? I can provide any additional info.
> 
> Cheers,
> Hiren


A single SACK can contains enough information to trigger a retransmit.

If you absolutely want to see the old 3 dupack in action, you also want
to disable SACK.