[GH-ISSUE #35] TCP is broken #32

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opened 2026-03-02 07:11:12 +03:00 by kerem · 2 comments
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Originally created by @sticky333 on GitHub (Sep 11, 2017).
Original GitHub issue: https://github.com/hwdsl2/docker-ipsec-vpn-server/issues/35

Hi guys. I've installed vpn with a docker container behind a NAT. I'm trying to connect to my network and I get some problems with tcp connections from shrew. Ping works fine but if I connect through TCP after a while tcp is broken. From my client I see that packets a going out through vpn server but not coming back. At the destination host I see a lot of retransmission packets. Can you help me to solve this issue? p.s. from MacOS everything works well but not from shrew.

Originally created by @sticky333 on GitHub (Sep 11, 2017). Original GitHub issue: https://github.com/hwdsl2/docker-ipsec-vpn-server/issues/35 Hi guys. I've installed vpn with a docker container behind a NAT. I'm trying to connect to my network and I get some problems with tcp connections from shrew. Ping works fine but if I connect through TCP after a while tcp is broken. From my client I see that packets a going out through vpn server but not coming back. At the destination host I see a lot of retransmission packets. Can you help me to solve this issue? p.s. from MacOS everything works well but not from shrew.
kerem closed this issue 2026-03-02 07:11:12 +03:00
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@hwdsl2 commented on GitHub (Sep 12, 2017):

@sticky333 Hello! Aside from possible network issues (maybe try a different server provider?), because the Shrew Soft VPN client hasn't been updated for a long time, it is likely to contain bugs and it's impossible for us to troubleshoot the issue for you. You may want to instead try the IPsec/L2TP mode using the built-in Windows client [1].

[1] https://github.com/hwdsl2/setup-ipsec-vpn/blob/master/docs/clients.md

<!-- gh-comment-id:328743004 --> @hwdsl2 commented on GitHub (Sep 12, 2017): @sticky333 Hello! Aside from possible network issues (maybe try a different server provider?), because the Shrew Soft VPN client hasn't been updated for a long time, it is likely to contain bugs and it's impossible for us to troubleshoot the issue for you. You may want to instead try the IPsec/L2TP mode using the built-in Windows client [1]. [1] https://github.com/hwdsl2/setup-ipsec-vpn/blob/master/docs/clients.md
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@sticky333 commented on GitHub (Sep 12, 2017):

Hello, thank you for your reply. I've solved the issue with broken TCP. The main reason is that mtu on interface has been installed to 1500 and as a result icmp was working but tcp not. Anyway, I've installed additional openswan packages to my host and now I can connect to my VPN using network-manager without shrew or any additional software. p.s. As I understood, I can't use L2TP mode because of NAT behind the server.

<!-- gh-comment-id:328984391 --> @sticky333 commented on GitHub (Sep 12, 2017): Hello, thank you for your reply. I've solved the issue with broken TCP. The main reason is that mtu on interface has been installed to 1500 and as a result icmp was working but tcp not. Anyway, I've installed additional openswan packages to my host and now I can connect to my VPN using network-manager without shrew or any additional software. p.s. As I understood, I can't use L2TP mode because of NAT behind the server.
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starred/docker-ipsec-vpn-server#32
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