[CentOS] database node / possible SYN flooding on port 3306

Leon Fauster leonfauster at googlemail.com
Fri Jul 20 10:56:53 UTC 2018


Hi folks,

I have here a database node running

# rpm -qa | grep mysql-server
mysql55-mysql-server-5.5.52-1.el6.x86_64

on

# virt-what 
vmware


that seems to have a connection problem:

# dmesg |grep SYN |tail -5
possible SYN flooding on port 3306. Sending cookies.
possible SYN flooding on port 3306. Sending cookies.
possible SYN flooding on port 3306. Sending cookies.
possible SYN flooding on port 3306. Sending cookies.
possible SYN flooding on port 3306. Sending cookies.


I adapted already following:

# sysctl -a |grep -E 'maxconn|syn_backlog'
net.core.somaxconn = 2048
net.ipv4.tcp_max_syn_backlog = 2048


but ListenOverflows and ListenDrops values are still high
 
# cat /proc/net/netstat | awk '{print $21 "-" $22 }'
ListenOverflows-ListenDrops
13568-13568

any suggestion? 

--
Thanks,
LF





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