Hi, I would like to have MTU 1500 for PPPoE over VLAN. So to accommodate the pppoe header I set the MTU of the VLAN interface to 1508. This results in the PPPoE status showing MRU 1500 but MTU increased only to 1496. I tried setting higher values, also on the physical interface and the max-mtu o…

My ISP fixed it :slight_smile: [image]

ISP may not support full 1500 MTU on PPPoE. Either on purpose or by misconfiguration.

[image] Virsacer: MTU increased only to 1496 1500 - 4 VLAN = 1496 Ask the ISP. The "MTU" must not be changed anywhere, only on PPPoE for supprot 1500 MTU/MRU, but only if your ISP allow you to do so. [image] How to force "Actual MTU" on PPPoE client General …

[image] rextended: The "MTU" must not be changed anywhere Explain this then MTU for PPPoE over VLAN - #5 by Znevna You are not the first to make this claim anyway. I did complain to support about the behaviour that MikroTik had until RouterOS 7.2 regarding the PPPoE client always trying to…

If the hardware is made by MikroTik, and the interface has a value for the L2MTU field, then there is no need to increase or modify the MTU value of any underlaying interface. They can all keep the default value of 1500. What you did not do in your screencap, was to do recommended thing and set Max …

So, to summarize: there is no RFC or standard that recommends blindly hardcoding Max MTU/MRU over the documented auto-negotiation process. Furthermore, your method of doing so while intentionally ignoring the parent interface MTU actually breaks RouterOS's Change TCP MSS behaviour, forcing users to…

I've had a headache dozens of times, for wrong labels (L3MTU / L2MTU)... but my entire customers network has an L3-MTU of 1500, with the exception of some non-MikroTik point-to-points which also mean L2MTU by MTU and need to be increased to allow PPPoE+VLAN to pass... VLAN can not consider (L3)MT…

Change TCP MSS = Yes in the default Profile is a hack made for all the PPP protocols that need to reduce the MSS because their MTU is most of the time smaller than the default 1500. It actually increases processing resource usage (same as when you add a FW mangle rule that inspects the TCP SYN packe…

[image] CGGXANNX: NOT the ethernet layer MTU I did not mention in any of my posts ethernet layer MTU, I don't know why you brought that up. Thought you meant the L2 MTU, I think you were just reffering to the parent interface L3 MTU here which in RouterOS is MTU. Right, so in case that the I…

It might be the lazy way, but it's the wrong way: As other have mentioned above, for MikroTik devices, what important is the L2MTU value. That changing MTU produces the effect is only due to the way RouterOS automatically calculates Max MRU and Max MTU when not set. But changing the MTU value …

Thanks guys! [image] Faceplate5158: Sounds like if this doesn't work for you there's something not quite right at the ISP end. The standard is RFC 4638: "baby jumbo frames". Maybe there's anything online from your ISP about this? Its a smaller regional ISP - not much to find online... But R…

MTU for PPPoE over VLAN

RouterOS General

S8T8 June 1, 2026, 6:58pm 27

Probably not useful in you context but in a other topic I tried solutions suggested by CGGXANNX and Rextended,
for me with PPPoE WAN + VLAN two are the options:

mss=no + MTU/MRU=1500
or
ethernetX and VLAN MTU=1508 with MTU/MRU=auto

be careful with keepalive-timeout , disabling will keep PPPoE active also il connectivity is down, then a Netwatch script is mandatory.