Category:Incoming L2TP: Difference between revisions

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=== MTU ===

The payload size (MTU) of traffic going through the L2TP tunnel will be lower than that of the underlying ISP - this is due to the extra 'headers' that are appliued to make the tunnel.

The payload

Some L2TP clients may auto discover the MTU, but you may want to specify it in your L2TP client configuration so as to obtain the optimum size.

You'd first want to find out what the maximum MTU is of your underlying ISP. you can do this with some pings, see our [[MTU|MTU Page]]. Once you know your MTU, you can calculate what the L2TP MTU should be.

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* Generally, the L2TP MTU would be 38 bytes less than the MTU you have on the underlying internet connection.

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* To find out the MTU of your underlying internet connection, see ~~out~~ [[MTU|MTU Page]]

* To find out the MTU of your underlying internet connection, see our [[MTU|MTU Page]]

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* Generally, the L2TP MTU would be 38 bytes less than the MTU you have on the underlying internet connection.

* In theory fragments will work to allow 1500 MTU on our service, but fragments are inefficient, and if everyone sends fragmented packets that could degrade the service.

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Ethernet 1500 1500

802.11Q* - 4* 1500 (* Treated as part of the ethernet header and doesn't affect the MTU)

802.11Q* - 4* 1500 * Treated as part of the ethernet header and doesn't affect the MTU

PPPoE - 6 1494

PPP - 2 1492 <-- ~~the~~ MTU of the underlying internet connection

PPP - 2 1492 <-- The MTU of the underlying internet connection

IPv4 - 20 1472

UDP - 8 1464

L2TP - 6 1458

(HDLC) - 2 1456

PPP - 2 1454 <-- ~~the~~ MTU of the L2TP service

PPP - 2 1454 <-- The MTU of the L2TP service

=== Port forwarding on some 'Mobile Broadband' routers ===