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TCP Retransmission / RST, ACK - Application Freezing

Carlos Cesario

Hello, 

We are having a stranger problem when accessing by VPN (IPSEC Site to Site) a web application. The WEB application when accessed by VPN stay loading Loading and freeze. After using Wireshark on this server that hosting the web application I could some retransmission events (image attached)

My troubleshooting steps until now:

- Create a DNAT rule on Head office and try access the same aplication by WAN address from Branch office, and the application it works as expected.

- Accessing this application over the same LAN (from Head Office)  it works as expected.

- Disable all IPS rules on Firewall Rules VPN-TO-VPN. Not effect, not working

- Change WEB application port on Hosting web server, not working

- Adding bypass stateful firewall rules on BO device and HO device the access it works as expected. (With This I supposed that there iare something on XG device that can be causing it)

All others access (SSH, CIFS, RDP, form BO to HO over this VPN it works)

Could someone has any tip for this ?

Regards

Carlos



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  • 0

    Hello Carlos,

    Thank you for contacting the Sophos Community!

    Could you please try changing the MTU size in the IPsec tunnel for these subnets or hosts. Modify as per your network, also you don't need to add the whole subnet but have only one host.

    iptables -t mangle -I POSTROUTING -s 192.168.1.0/24 -d 10.10.0.0/22 -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 900;
    iptables -t mangle -I POSTROUTING -s 10.10.0.0/22 -d 192.168.1.0/24 -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 900;

    Are both sides of the IPsec XG?

    Can you confirm if all the packets are leaving the interface ipsec0?

    Are you running v18 or v17?

    Regards,

  • 0 in reply to emmosophos

    Hi ,

    I just applyed the iptables rules and disable bypass rules, and the problem happen.

    Answering your question about if the traffic pass by ipsec interface, no the traffic pass by xfrm interface, because the Ipsec Tunnel is type Tunnel mode..

    And other information, In these BO peers I have a transparent interface (layer 2) connected to HO, like a Point to Point  ... even using this interface I got the same problem.

    Regards

    Carlos

  • 0 in reply to Carlos Cesario

    Hello Carlos,

    Thank you.

    Oh, I miss read the part about the bypass make it work, then the command wouldn't make too much of a difference.

    Do you see something in the Live Log, that might give us a clue?

    Regards,

  • 0 in reply to emmosophos

    Hello

    Yesterday, debbuging it with more details, I could see that when the application freeze, it is generated this event (captured by drppkt)

    But I believe that is a result of " TCP Reset Connections"  previous sent. You can see in this log a *R* flag .

    I re enable the by pass rule as workaround for it.

    DO you have any other tip ?

    Best regards

    Carlos

  • 0 in reply to Carlos Cesario

    Likely a Application issue. 

    Those F/R Packets are dropped because they are duplicated. So the App or the client is closing the session. 

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