*SOLVED* SMTP-Problem with OpenVZ-Kernel
Hello, I use a VPS as SMTP-Relay. Now I discovered a problem. When my VPS is trying to connect to one specific Firewall on Port 25 the communication is stopped. If I simulate this with telnet, it looks like this : ---------------snipp------------------------ Telnet 1.2.4.6 25 Trying 1.2.3.4... Connected to 1.2.3.4. Escape character is '^]'. 2 --------------------------------------------- As you can see there comes an answer from this Firewall but the Packet is not transferred completely. I have tried this with OpenVZ-Kernels between 2.6.8-022stab061.1 and 2.6.8-022stab077.1 with and without SMP. My Machine is a DualXeon-Server and the problematic firewall is a Netscreen 5 GT with Trendmicro Antivirus. By the way, if i disable the Trendmicro Antivirus it works but this is not really an option. Also i have tried the test kernel 2.6.16-026test012.1 and this works quite perfectly. Does anybody have a suggestion for me or do i have to wait until kernel 2.6.16 becomes stable?
Have you ensured the packets are hitting the HN/VPS? I would use ngrep and inspect port 25 for traffic. If your firewall is problematic, I would say the problem lies there before the kernel version.
Yes, I have observed communication between the firewall and my Server. It is ok if the trendmicro antivirus is disabled. The funny thing is that any other server can communicate to port 25 on this firewall without any problem. I have tried different machines with different hardware. This problem arises on every machine with OpenVZ-Kernel-2.6.8. The SMTP Relay on the VPS communicates to many other servers without a problem. Because it works with the new OVZ-Kernel 2.6.16 , I think it is somehow a network problem with 2.6.8.
You need to collect tcpdump logs from all the machines participating in communication to understand where things go wrong. It can be some kind of misconfiguration (e.g. ECN).
The only machine where i can do a tcpdump is the OpenVZ-Server. A dump is attached.
Re: SMTP-Problem with OpenVZ-Kernel -Solved-
Hi, this is exactly my problem. After reading this Bugreport ( http://bugzilla.openvz.org/show_bug.cgi?id=210 )and the discussion about it i have done "echo 0 /proc/sys/net/ipv4/tcp_window_scaling". Now my mailserver works fine .