Strange MTU behavior PPPOE

[RZomerman]

Hi everyone, 

I have a PPPOE connection to my telco which gives me an MTU of 1492. 

However the device seems to be unable to process a packet >1472 bytes that I send out to the internet.

My setup is rather simple, ISPmodem->eth1-CP4400->Mngt-client

when the client is pinging to a public IP address, it all goes fine, as long as the packet size is smaller than 1473. I can send up to 1472, but as soon as I go over it packets are dropped. Which causes weird behaviors obviously.

I'm on R80.20 Build: 101

Any idea as to why packets >1472 are dropped? Is there a way to find out what is happening?

I had Junipers/USG's connected to the same link and those all work fine.. 

I don't have a support contract as this is my demo device to run some tests on at home..

[RZomerman]

fixed!

The trial license allowed me to update to 80.30 and it's working now.. 

[Timothy_Hall]

It is possible that the ICMP packet somehow got tangled up with SecureXL under R80.20 since SecureXL does not support Point-To-Point links, but ICMP is never supposed to be accelerated by SecureXL at all so that seems consistent with some kind of bug that was fixed.

[Maarten_Sjouw]

With the do not fragment bit set and an IP header of 20 bytes this would be expected behavior.