I can't speak to the Ubiquiti equipment, but PPPoE adds 8 bytes of overhead. So MTU will normally be 1492, and the PPPoE client will normally enforce this by modifying MTU advertisements from the client side.
What you want to do seems comparable to carrying 8 passengers in an 8 seat van, forgetting that the driver takes up 1 seat. -----Original Message----- From: AF <af-boun...@af.afmug.com> On Behalf Of Adam Moffett Sent: Monday, August 12, 2019 11:22 PM To: AnimalFarm Microwave Users Group <af@af.afmug.com> Subject: Re: [AFMUG] PPPoE MTU Newb confusion If it's not clear.....I want to carry a mother truckin 1500 byte packet from the end user to the internet. I have full control of the path between the pppoe client and server, so I didn't anticipate this being a problem, but somehow it's a problem. On 8/13/2019 12:04 AM, Adam Moffett wrote: > So I've never done much with PPPoE. > > In my test setup I have a Mikrotik PPPoE Server set with "Max MTU" of > 9216. This is a CCR with an actual max of 10,000+ bytes. > > The PPPoE client is a Ubiquiti ER-X-SFP. The Ubiquiti client will not > allow me to set an MTU on the PPPoE interface higher than 1500. They > physical interface has an MTU of 2016 (maximum for this platform). > > The active session on the mikrotik server reports "Actual MTU" of > 1480, and fragments packets larger than that. Packets larger than 1492 > are silently dropped. > > There's a switch between the tik server and ubnt client, and it has > jumbo frames enabled and has an MTU of 9216. > > So I'm 100% confused. > If the MTU on the client is 1500, where are the limits of 1480 and/or > 1492 coming from? > Why in the ever loving hell does the Ubiquiti router not allow an MTU > higher than 1500 on the PPPoE client? > > -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
