PPPoE RFC4638 support

[fcz]

Hello,

I have recently bought a Keenetic KN-1910 Skipper, but it seems that it lacks RFC4638 support. I set 1500 MTU on the PPPoE connection but a DF ping still shows max MTU of 1492. For RFC4638 support, the ethernet interface would need an MTU of at least 1510 bytes, since it needs to transport packet payload + VLAN tag (802.1q - 2byte) and PPPoE header (6+2=8bytes).

My ISP supports RFC4638 and it uses VLAN + PPPoE. Under a different router running OpenWRT, I can set MTU of 1510 and have this working.

Would it be possible to add this feature into the next KeeneticOS release, or is there a way to achieve the same permanently (into saved settings) via CLI?

 

Thanks,
FC

 

 

[RuslanK]

Might be useful for someone, looks like RFC4638 is supported (tested in 4.3), the only thing you need to set MTU using CLI:

interface ISP ip mtu 1508
system configuration save

When PPPoE connection is restarted I am able to increase ICMP packet size up to 1472 (which corresponds to MTU 1500 minus 28 bytes header)

The only drawback is that UI settings show error for the field,  if you need to change any setting on this page, it will not let you save it. The workaround is to reduce it to 1500 in UI, save, and change using CLI again. This could be something for Keenetic team to consider fixing (bump valid value to MTU size field to 1508).