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binhorp
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Doubts about pppoe MTU

Sat Jul 19, 2014 7:19 pm

Hello everyone! I wonder if working with pppoe MTU in 1500 and cause some kind of problem, after a week of problems with some websites that do not show images, our supplier link pointed as a solution to replace the pppoe server MTU to 1500 is that this value is correct ?
grateful for your attention!
 
onnoossendrijver
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Re: Doubts about pppoe MTU

Sat Jul 19, 2014 7:51 pm

Normally PPPoE supports maximum MTU of 1492. I you need more then BOTH server and client need to support RFC4638.
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sjoram
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Re: Doubts about pppoe MTU

Sun Jul 20, 2014 12:47 pm

My PPPoE MTU is 1432 but I had to use MSS clamping to reduce MSS on TCP SYN packets to 1386.
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RouterBOARD RB750GL - Xilo FTTC (VDSL)
 
samsung172
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Re: Doubts about pppoe MTU

Sun Jul 20, 2014 3:13 pm

if running pppoe server to a wlan Interface - mtu could be 1500.

If run to a Ethernet Interface, With 1500 bytes mtu - it should be set to 1492 due to 8 byte pppoe.

Its possible to set mtu to 1508 troug Whole net and run 1500 to pppoe server. I suppose you have a change mss setting to Your server running at 1500 to have it to work. this makes fragmentation and will reduce speed to Your net.
 
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sjoram
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Re: Doubts about pppoe MTU

Sun Jul 20, 2014 5:15 pm

If I understand your problem correctly, see screenshots in below file.
You need one rule to cover in interface and another rule to cover out interface (same interface on both rules - your PPP interface).

http://www.oram-net.net/public/ROS-MSS.pdf
RouterBOARD RB750 - Xilo ADSL2+ (Annex M)
RouterBOARD RB750GL - Xilo FTTC (VDSL)
 
samsung172
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Re: Doubts about pppoe MTU

Sun Jul 20, 2014 11:41 pm

This is a "hack" to solve the mtu issue. Fragment packages, and ""fill" net With a lot of small packages. Works well on small net, but will make troble on large net. pps will doble, and CPU/ram etc on routerboard will raise a lot - Better to have the correct mtu to Interface if possible

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