[Golpesar]

Hi dear friends,
I use Psiphon as a VPN.
The software works well when the router is powered by OpenWRT.
However, the same version and the same device cannot connect when the router is powered by DD-WRT.

Would you please help me understand if there is any concept I am missing?

Both routers are using an ADSL modem to private internet for users.

Thanks in advance.

[Alozaros]

well..as you may believe...more details are needed...
otherwise there is no idea why...

router model, build number running, OpenVPN set up...cover the private details...pic's will tell a better story..

also did you follow the OpenVPN guide from Advanced Networking sticky's

finally OpenVPN debug log will expose the verbose detail..add verb 6 to advanced vpn commands box and post the output...along with pics and ect.

[Per Yngve Berg]

Have you Enabled IPsec/L2TP pass-through?

[Golpesar]

Thanks for your kind and prompt reply.
I have no access to the router now.
But I will collect some useful information and send here.

However, I have no OpenVPN config on the router.
I will check if the IPsec/L2TP pass-through is set.
Where should I find this option?

Regards,

[kernel-panic69]

Security -> VPN Passthrough tab. And I absolutely love how some folks don't understand that Psiphon is a client app and want to point to another feature (OpenVPN).

[Alozaros]

[Golpesar]

Hi dear friends,

I had a chat with chatgpt regarding this issue. Interestingly, it resolved the issue. Now I am writing and using Psiphon via dd-wrt.
I asked for a technical detail and it provided me with the following:


Title: Psiphon Does Not Work Behind DD-WRT (Wireless Station Mode) – Fixed by Adjusting MTU and Firewall Filters

Hello everyone,

I want to share a networking issue I had and the solution, in case it helps others.

Network Setup:

Main router: OpenWRT

Two downstream routers

Both downstream routers connect wirelessly to the main router (Wireless Station mode)

Both then redistribute internet wirelessly to clients

One downstream router runs OpenWRT

The other downstream router runs DD-WRT

The Problem:

Psiphon works perfectly behind the OpenWRT downstream router.

However, behind the DD-WRT downstream router, Psiphon would not connect. It would hang indefinitely.

Root Cause Analysis

Since Psiphon worked behind OpenWRT but not DD-WRT, the issue was clearly configuration-related on the DD-WRT side.

Psiphon uses:

HTTPS tunnels (port 443)

SSH tunnels (port 22)

Obfuscated traffic

Long-lived TCP sessions

Sometimes UDP/QUIC

These are sensitive to:

MTU mismatches

Fragmentation

Deep packet inspection

Certain firewall filters

In wireless station + double NAT environments, MTU issues are very common.

What Fixed the Problem (DD-WRT)

I did NOT disable the full SPI firewall.

The issue was solved by:

Disabling only these two firewall filters:

Security → Firewall

Filter Multicast → Disabled

Filter IDENT (Port 113) → Disabled

SPI Firewall itself remained enabled.

Manually setting MTU to 1400

Setup → Basic Setup

MTU → Manual

Value → 1400

After these two changes, Psiphon connected immediately and worked normally.

Again thank you.
And of course thank you chatgpt.

[kernel-panic69]

Thanks for the update. Glad you found a solution.