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RZomerman
Explorer

Strange MTU behavior PPPOE

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..

 

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3 Replies
RZomerman
Explorer

fixed!

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

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Timothy_Hall
Legend Legend
Legend

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.

 

Gateway Performance Optimization R81.20 Course
now available at maxpowerfirewalls.com
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Maarten_Sjouw
Champion
Champion

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