Telekom VDSL2 MTU


if I switch to VDSL2 (100/40 MBit), in the PPP setup I select VDSL as interface and INET_VLAN 7, but what MTU size should I use?

For PPPoE I always used MTU 1492, is it the same for VDSL2?

Did Telekom specified any special size of MTU?

No. I googled and some are using 1500. Or is it better not to fill in any values so it’s automatic? I don’t know.

If you leave it empty, you will be assigned a MTU by the ISP.

You can always use “tracepath” and it will tell you the MTU over that path.


an MTU of 1492 works fine for me on a VDSL2-Line (Running Mode 17A) with a Speed of 100/40 MBit/s (Owner/Operator of my TAL: Deutsche Telekom, My Provider: Vodafone)

I’m using German Telekom VDSL(2) for years now with a fixed MTU of 1492 without any problems.
I’ve been always sure, that this is the right value. As @ms said, tracepathing is always a good idea.

I had to reduce the MTU to 1488 because the PPP encapsulated packets from the IPFire to the modem exceeds 1500 bytes if 1492 (if i leave unset) is configured. I’m not sure if my red interface (NanoPi R1) or the modem (Fritzbox 7412 in fullbridge mode) cannot handle 1504 byte packets.