I have configured a nginx http webserver to serve a site on CentOS 6 Virtual machine. every things are works fine but when I connect to site from a special ISP, the site wait and after a while respond 504 Gateway timeout. This occurs only from this ISP not any else.
After several search I found that this problem may be related to MTU of my interface. I changed MTU to 1400 but still the problem exist. Can anyone help me?
Edit
You can see traffic capture in this image:
I have changed MTU in server to 1400 but server responses MSS=1460 that mean MTU is 1500. When I capture traffic and check the MSS on other ISPs, I get MSS=1360 and this is correct.
You can see server packets in this image:
