netdev - Re: Something hitting my total number of connections to the server

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Date:   Tue, 22 Aug 2017 06:02:06 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Akshat Kakkar <akshat.1984@...il.com>
Cc:     David Laight <David.Laight@...lab.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: Something hitting my total number of connections to the server

On Tue, 2017-08-22 at 11:12 +0530, Akshat Kakkar wrote:
> There are multiple hosts/clients. All are mainly windows based.
> 
> Timestamp is not used as my clients mainly are windows based and in
> that it tcp timestamp is by defauly disabled.
> 
> sysctl is as follows:
> 
> kernel.shmmax = 68719476736
> kernel.shmall = 4294967296
> kernel.pid_max=4194303
> vm.max_map_count=131072
> kernel.sem=250 32000 32 250
> 
> net.netfilter.nf_conntrack_generic_timeout = 300
> net.netfilter.nf_conntrack_tcp_timeout_syn_sent = 60
> net.netfilter.nf_conntrack_tcp_timeout_syn_recv = 30
> net.netfilter.nf_conntrack_tcp_timeout_established = 7200
> net.netfilter.nf_conntrack_tcp_timeout_fin_wait = 60
> net.netfilter.nf_conntrack_tcp_timeout_close_wait = 30
> net.netfilter.nf_conntrack_tcp_timeout_last_ack = 30
> net.netfilter.nf_conntrack_tcp_timeout_time_wait = 60
> net.netfilter.nf_conntrack_tcp_timeout_close = 10
> net.netfilter.nf_conntrack_tcp_timeout_max_retrans = 300
> net.netfilter.nf_conntrack_tcp_timeout_unacknowledged = 300
> net.netfilter.nf_conntrack_udp_timeout = 30
> net.netfilter.nf_conntrack_udp_timeout_stream = 180
> net.netfilter.nf_conntrack_icmp_timeout = 30
> net.netfilter.nf_conntrack_events_retry_timeout = 15
> net.core.rmem_max = 8388608
> net.core.wmem_max = 8388608
> 
> net.ipv4.tcp_tw_reuse=1
> net.ipv4.tcp_tw_recycle=1

This is exactly what I feared.

We do not support tcp_tw_reuse = 1 AND tcp_tw_recycle = 1

This is a very well known bad combination.



> net.ipv4.tcp_fin_timeout=30
> net.ipv4.tcp_keepalive_time=1800
> net.ipv4.tcp_keepalive_intvl=60
> net.ipv4.tcp_keepalive_probes=20
> net.ipv4.tcp_max_syn_backlog=4096
> net.ipv4.tcp_syncookies=1
> net.ipv4.tcp_sack=1
> net.ipv4.tcp_dsack=1
> net.ipv4.tcp_window_scaling=1
> net.ipv4.tcp_syn_retries=3
> net.ipv4.tcp_synack_retries=3
> net.ipv4.tcp_retries1=3
> net.ipv4.tcp_retries2=15
> net.ipv4.ip_local_port_range=1024    65535
> 
> net.ipv4.tcp_timestamps=0
> 
> net.core.netdev_max_backlog=10000

This is an insane backlog.

> net.core.somaxconn=100000
> net.core.optmem_max=81920
> 
> net.netfilter.nf_conntrack_max=524288
> net.nf_conntrack_max=524288
> net.ipv6.conf.all.disable_ipv6 = 1
> fs.file-max=1000000
> 
> net.ipv4.tcp_no_metrics_save = 1
> net.ipv4.tcp_max_syn_backlog = 10240
> net.ipv4.tcp_congestion_control=htcp
> 
> net.ipv4.tcp_rfc1337 = 1
> net.core.netdev_max_backlog = 65536

This is a crazy backlog. Do not do that.


> net.ipv4.tcp_max_tw_buckets = 1440000
> 
> net.core.rmem_max = 134217728
> net.core.wmem_max = 134217728
> 
> 
> 


It looks like your sysctls have been set to unreasonable values.