Jul 06, 2016 · Thank goodness there was MikroTik router on the client end of the link. MikroTik (and Linux) have a feature called “Clamp to pmtu” in mangle. This feature dynamically changes the MTU settings to match the smallest MTU from point to point and thereby prevents fragmentation and the weirdness I previously described. Here is my fix:
PPTP versus L2tp/IPSec bandwidth loss - Best Practices Apr 18, 2018 MikroTik Routers and Wireless - Products: LHG 60G MikroTik is a Latvian company which was founded in 1996 to develop routers and wireless ISP systems. MikroTik now provides hardware and software for Internet connectivity in most of … Path MTU Discovery - Wikipedia
I played with the settings, but we'd lose connectivity to our other customers, so I ended up setting it back to what I had set it to before (ip mtu 1460 and ip tcp adjust-mss 1420) and suddenly I can pass 1452 size packets, and the customer's L2TP VPN conneciton is working again. It worked for another two weeks, and then it stopped working again.
MTU Size This has been set up by Sky for optimal performance, you should not need to change this. The normal MTU (Maximum Transmit Unit) value for most Ethernet networks is 1500 Bytes, or 1492 Bytes for PPPoE connections.
Feb 02, 2006
I just finish setting a gre tunnel with IPSEC and 3DES encryption. When I used the default settings, configured by the SDM, it set the tunnel MTU to 1420. With that default setting I was able to bring up the tunnel, but simple tcp services would not work, like viewing a HTTP server of using FTP. So Basic Mistakes by ISP's on Network setup & BGP - MikroTik MTU and TCP-MSS Configuration On a Mikrotik router the TCP-MSS gets picked up and set in a mangle rule. For this example we will set the MSS for traffic going over the PPPoE interface. We will set the MSS at 1452 which is calculated as per below: MSS = MTU of interface - TCP Header - IP Header MSS = 1492 - 20 - 20 MSS = 1452