Catalina insists upon MTU=1400 for IPsec connections, but apparently this is too large for Unitymedia networks (big German IP provider). How can I permanently reduce the MTU for IPsec connections to (lets say) 1280?
MacBook
Usually IPsec is configured via profiles, but the Config Profile Reference manual doesn't mention setting the mtu at all. AFAICT nobody thought about that.
Of course I have restarted both Wifi and embedded IPsec connection after changing the Wifi mtu. I saw the reduced mtu for the Wifi network interface, but the IPsec connection was at 1400, still.
I can reduce the IPsec mtu on the command line (ifconfig ipsec0 mtu 1280), but this is lost when the IPsec connection is reestablished. Its not permanent.
Nope, this did not work. ifconfig ipsec0 still shows mtu 1400, even though the Wifi interface is set to mtu 1380.
You might have to restart after you set the MTU. But as I said, I believe it should work. I've never done it so I can't be sure.
I actually meant restart your Mac but you may want to wait for another response.
I believe this should work. Open System Preferences > Network. select Ethernet or WiFi. Click the "Advanced" button. Click the "Hardware" tab. Change "Configure:" to Manually. Then choose "MTU:" > Custom.
How can I permanently fix the MTU used for IPsec?
