Re: [AFMUG] PPPoE MTU Newb confusion
The Ubiquiti ER-X-SFP allows a 2018 byte MTU on all the physical interfaces, but will not allow an MTU larger than 1500 bytes on the PPPoE interface. I guess this thing is going in the garbage. -Adam On 8/13/2019 8:57 AM, Dennis Burgess via AF wrote: If you can set the L2MTU on the UBNT radio to 1508 or better yet 1510, then you should be able to specify the MTU of the PPPoE to 1508, then you should be able to have a full 1500 byte packets without fragmentation. Of course, if UBNT can't do this, I would recommend not using them, but I regress. Else you will have to use a device that can do that without issues, or suffer fragmentation, not somtghing that is uncommon. It really won't make much difference in the grand scheme of things. Dennis Burgess, Mikrotik Certified Trainer MTCNA, MTCRE, MTCWE, MTCTCE, MTCINE, MTCSE, HE IPv6 Sage, Cambium ePMP Certified Author of "Learn RouterOS- Second Edition" Link Technologies, Inc -- Mikrotik & WISP Support Services Office: 314-735-0270 Website: http://www.linktechs.net Create Wireless Coverage's with www.towercoverage.com -Original Message- From: AF On Behalf Of Ken Hohhof Sent: Tuesday, August 13, 2019 7:16 AM To: 'AnimalFarm Microwave Users Group' Subject: Re: [AFMUG] PPPoE MTU Newb confusion 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 On Behalf Of Adam Moffett Sent: Monday, August 12, 2019 11:22 PM To: AnimalFarm Microwave Users Group 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 -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
Re: [AFMUG] PPPoE MTU Newb confusion
Adam, General comment: The packets aren't actually being fragmented. Most TCP packets have the Do-Not-Fragment bit set, all equipment will honor (except VPNs). However, when using a Mikrotik as a PPPoE server, it automatically sets up some IP Mangle rules that modify the TCP MSS (maximum segment size) during TCP session establishment on any traffic coming from the PPPoE client and adjusting the TCP MSS down at least 8 bytes to accommodate the smaller overall MTU. Specific to your equipment, I would guess the UBNT edge router doesn't support RFC4638, which specifically describes having an MTU larger than 1492 for PPPoE traffic. The Mikrotik does (unless you're on a REALLY old version of RouterOS). On 8/13/19 6:57 AM, Dennis Burgess via AF wrote: If you can set the L2MTU on the UBNT radio to 1508 or better yet 1510, then you should be able to specify the MTU of the PPPoE to 1508, then you should be able to have a full 1500 byte packets without fragmentation. Of course, if UBNT can't do this, I would recommend not using them, but I regress. Else you will have to use a device that can do that without issues, or suffer fragmentation, not somtghing that is uncommon. It really won't make much difference in the grand scheme of things. Dennis Burgess, Mikrotik Certified Trainer MTCNA, MTCRE, MTCWE, MTCTCE, MTCINE, MTCSE, HE IPv6 Sage, Cambium ePMP Certified Author of "Learn RouterOS- Second Edition" Link Technologies, Inc -- Mikrotik & WISP Support Services Office: 314-735-0270 Website: http://www.linktechs.net Create Wireless Coverage's with www.towercoverage.com -Original Message- From: AF On Behalf Of Ken Hohhof Sent: Tuesday, August 13, 2019 7:16 AM To: 'AnimalFarm Microwave Users Group' Subject: Re: [AFMUG] PPPoE MTU Newb confusion 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 On Behalf Of Adam Moffett Sent: Monday, August 12, 2019 11:22 PM To: AnimalFarm Microwave Users Group 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 -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
Re: [AFMUG] PPPoE MTU Newb confusion
If you can set the L2MTU on the UBNT radio to 1508 or better yet 1510, then you should be able to specify the MTU of the PPPoE to 1508, then you should be able to have a full 1500 byte packets without fragmentation. Of course, if UBNT can't do this, I would recommend not using them, but I regress. Else you will have to use a device that can do that without issues, or suffer fragmentation, not somtghing that is uncommon. It really won't make much difference in the grand scheme of things. Dennis Burgess, Mikrotik Certified Trainer MTCNA, MTCRE, MTCWE, MTCTCE, MTCINE, MTCSE, HE IPv6 Sage, Cambium ePMP Certified Author of "Learn RouterOS- Second Edition" Link Technologies, Inc -- Mikrotik & WISP Support Services Office: 314-735-0270 Website: http://www.linktechs.net Create Wireless Coverage's with www.towercoverage.com -Original Message- From: AF On Behalf Of Ken Hohhof Sent: Tuesday, August 13, 2019 7:16 AM To: 'AnimalFarm Microwave Users Group' Subject: Re: [AFMUG] PPPoE MTU Newb confusion 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 On Behalf Of Adam Moffett Sent: Monday, August 12, 2019 11:22 PM To: AnimalFarm Microwave Users Group 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 -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
Re: [AFMUG] PPPoE MTU Newb confusion
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 On Behalf Of Adam Moffett Sent: Monday, August 12, 2019 11:22 PM To: AnimalFarm Microwave Users Group 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
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
