I am connected to my ISP via an ethernet cable, and that only provides me connection to the ISP’s private network. In order to get internet connectivity, I have to connect via an L2TP connection.
The provider declares the MTU must be set to 1460. I have Mikrotik RB2011UiAS router so it’s a bit more advanced setup than your typical router. I’ve set up the L2TP connection there and provided the correct MTU. Problem is, that is not enough.
When I connect to this router, say, a PC with a LAN card to an ethernet 2 interface of the router, the PC’s LAN connection still has 1500 MTU (OS is Win7). Some websites won’t load properly unles I type “netsh interface ipv4 subinterface “Name” set mtu=1460 store=persistent” in the command propmt on the PC.
Do I have to do this? Because of this, when, say, a friend visits my place with a notebook, I have to tell him to type this in his command prompt just to be able to use my wifi. And if he’s got an Android tablet, what do I do btw?Geometry Dash Lite I dunno what to type where to change the mtu on it.
There definetly must be a better solution. I mean, is there a way to somehow make this work without having to manually change MTU on all the devices?
I’m not at all familiar with the problem myself but this topic has been discussed several times on this place.
Here is a reference:
http://forum.mikrotik.com/t/which-mtu-size-should-i-set-on-my-interfaces/158444/1
Using a PPP profile for the L2TP connection with change-tcp-mss=yes should be sufficient, it certainly works for the L2TP service provided by AAISP in the UK.
Try add this to your router
/ip firewall mangle
add action=change-mss chain=forward new-mss=clamp-to-pmtu passthrough=yes protocol=tcp tcp-flags=syn comment=“Clamp MSS to PMTU for Outgoing packets”
add action=change-mss chain=output new-mss=clamp-to-pmtu passthrough=yes protocol=tcp tcp-flags=syn
OR
/ip firewall mangle
add action=change-mss chain=forward new-mss=1400 passthrough=yes protocol=tcp tcp-flags=syn tcp-mss=1401-65535