client initial SYN packet intermittently ignored.....resulting in sloooowwwww website

Notsobigkev · 09-10-2021, 06:01 AM

Hi, I am running Ubuntu 21.04 (have nothing to compare to previous vers) with Apache2 and am trying to launch a web server. I find when I connect to the server it will intermittently not respond to the initial client's SYN packet. This can be seen on Tshark traces. I have searched various forums which now suggest that parameters in /etc/sysctl may need tweaking.(still no joy) All attempts to fix have failed.
Would anyone have any other ideas on areas to address to effect a fix ?? I can't believe this a generic problem on 21.04. I have discounted a problem with internet access, routers etc

Should I bite the bullet and load up Fedora or Centos. ??

Windows, as a matter of principle, is not an option.

Still investigating.......

Many thanks

Kev

smallpond · 09-10-2021, 08:47 AM

SYN packet has nothing to do with the web server. It is part of TCP/IP protocol. Assuming you have a server accepting connections, not responding to SYN means you are either out of some resource: memory, network buffers, max connections, etc., or you are blocking connections with firewall.

Check the apache access and error log. If it drops SYN, apache should not see it at all.

Try making a simple listener with netcat (nc) and see if it does the same thing.

Notsobigkev · 09-10-2021, 02:56 PM

smallpond....or ....the tcp handshake has EVERYTHING to do with a web conversation as it's TCP based. Thank you for your input. I found the prob with a couple of anomolous routes and it's now fixed. You need to reign in your misguided advice and try and help peeps, instead of being a ..... xxxx night night

scasey · 09-11-2021, 03:18 PM

“a couple of anomolous routes” seems to me to be an example of “blocking connections”…
So smallpond did, in fact, point to the solution in addition to suggesting other possibilities.

Web servers are networking 7th layer things. The TCP conversation happens in the 3rd or 4th layer…I’m not sure which…I’m a 7th layer guy…

Glad the we were able to help. Please mark your thread solved.

TB0ne · 09-11-2021, 04:22 PM

Quote:

Originally Posted by Notsobigkev

smallpond....or ....the tcp handshake has EVERYTHING to do with a web conversation as it's TCP based. Thank you for your input. I found the prob with a couple of anomolous routes and it's now fixed. You need to reign in your misguided advice and try and help peeps, instead of being a ..... xxxx night night

So bad/incorrect routes aren't a network issue?? Good to know. And aren't the vast majority of network services TCP based?? Smallpond correctly said it was some sort of network issue; and it was.

smallpond · 09-12-2021, 08:01 AM

I think it's good that there is no age requirement on LQ.

rtmistler · 09-12-2021, 10:06 AM

Notsobigkev,

Please refrain from personal attacks moving forward.