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

[Nataraj]

On 07/20/2018 03:56 AM, Leon Fauster via CentOS wrote:
> 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? 

Use tools like tcpdump/wireshark  and further examination of logfiles to
determine where your attack is coming from, i.e. single IP address or
multiple ip addresses (BOT attack).

If attack is impairing your Internet service, contact your ISP.  Most
decent ISP's should deal with this situation for you.

If attack is not impairing your service and you choose to deal with it
yourself, then, if from a fixed IP address block that IP from your
firewall if you have one, otherwise, use IPtables on the server.  If
your having bot attacks, or blocking attack causes source IP address to
be changed, then look at fail2ban.  Basically you want to configure
fail2ban to limit the number of requests per unit of time and block IPs
that exceed that.  Also, consider weather your database needs to be
publicly accessible from the Internet.

Nataraj