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Network Troublshooting => Linux Servers Support => Topic started by: vlinux1 on March 14, 2008, 04:10:02 AM

Title: SMTP SERVICE GOING DOWN:possible SYN flooding on port 25.Sending Cookies
Post by: vlinux1 on March 14, 2008, 04:10:02 AM

Hello


I have configured a new qmail server and all services are working good.
After some time i found that SMTP services is frequently going down if i check
qmail stat it showing a big queue more than 20000. I tried to send mail from my server to gmail is not going but i can receive mail from Gmail.

I checked in log file it showing me a following error.

Mar 14 02:52:10 vjmail kernel: possible SYN flooding on port 25. Sending cookies.
Mar 14 02:56:39 vjmail kernel: possible SYN flooding on port 25. Sending cookies.


I am not able to send any mail.


Thanks in advance

Thanks
 

Title: Re: SMTP SERVICE GOING DOWN:possible SYN flooding on port 25.Sending Cookies
Post by: Ricky on March 16, 2008, 01:07:39 PM

Your smtp is being flooded.
What you need to do is enable filtering.

Configure rblsmptd ..
You can follow this guide : http://lifewithqmail.org/lwq.html  It has section for rblsmptd .

Title: Re: SMTP SERVICE GOING DOWN:possible SYN flooding on port 25.Sending Cookies
Post by: vlinux1 on March 18, 2008, 06:17:30 AM

Hi Ricky,

Thank you very much for your reply.
I've checked this link but how to configure this program. I am confused if you did it before then please let me know the procedure and i am using qmail from qmailrocks.


Thanks in advance
Vj

Title: Re: SMTP SERVICE GOING DOWN:possible SYN flooding on port 25.Sending Cookies
Post by: Ricky on March 20, 2008, 05:25:55 PM

Go here .. they have FAQs for rblsmtpd

http://www.tjsi.com/rblsmtpd/faq/

Title: Re: SMTP SERVICE GOING DOWN:possible SYN flooding on port 25.Sending Cookies
Post by: vlinux1 on March 23, 2008, 03:40:17 AM

Hello Ricky,

Thank you very Much for the link i will check and let you know.

THANK YOU VERY MUCH :)


Vj

Title: Re: SMTP SERVICE GOING DOWN:possible SYN flooding on port 25.Sending Cookies
Post by: vlinux1 on April 08, 2008, 05:54:53 AM

Hi Ricky&Gaurav

I installed & configure qmail on Redhat As and its working fine. Thanks for your help. Now issue is my mail server is behind a firewall and i also added open relay for my network but if is see /var/log/qmail/qmail-send/current it shows me a different network ips trying to use my smtp but they can't. I want to totally stop this other network's ip so what i can do?
I need any special security to do on my server.

Please help me regarding this.

Thanks in advance
Vj